The Taiwanese and Philippine Species of the Terrestrial Crabs Bresedium Serène and Soh, 1970 and Sesarmops Serène and Soh, 1970 (Crustacea: Decapoda: Brachyura), with Descriptions of Two New Species

Abstract

The genera Bresedium Serène and Soh, 1970 and Sesarmops Serène and Soh, 1970 are two closely related taxa inhabiting terrestrial or freshwater environments from the Indo-West Pacific. Based on morphological and molecular evidence, two new species from Taiwan, the Philippines and Indonesia are described in this study, viz. B. eurypleon n. sp. and S. mora n. sp. The new species can be distinguished from congeners by a suite of carapace, chelipedal, gonopodal and vulvar characters. Bresedium philippinense (Rathbun, 1914) is here shown to be a junior synonym of B. brevipes (De Man, 1889). A poorly known Philippine species, Sesarmops mindanaoensis (Rathbun, 1914), is redescribed from the type and fresh material, and is recorded for the first time from Taiwan.

BACKGROUND

Most sesarmid crabs (family Sesarmidae Dana, 1851) are common and important in mangrove regions; they are able to tolerate high temperatures and salinity fluctuations and have been the subject of many recent ecological studies (e.g., Lee 2015; YF Li et al. 2017; Theurkauff et al. 2018). Serène and Soh (1970: 391, 399, 400) established two new genera, Bresedium and Sesarmops, for several Indo-West Pacific species previously placed in Sesarma Say, 1817. Members of Bresedium are diagnosed by the lateral margins of the carapace being subparallel and the carapace appearing rectangular in shape, the male pleon has the telson distinctly inserted into the concave distal margin of somite 6, and the distal part of the male first gonopod is elongated and slender (Serène and Soh 1970). Species of Sesarmops are characterised by having a carapace that is as long as or longer than the exorbital width, the lateral margins of the carapace are prominently divergent posteriorly with the carapace appearing trapezoidal, the male pleon has an almost straight or only gently concave distal margin of somite 6 in which the telson is inserted, and the distal part of the male first gonopod is less elongate (Serène and Soh 1970).

Ng et al. (2008) commented that Bresedium and Sesarmops are sister taxa based on unpublished morphological and molecular data, and that some species of Sesarmops do not belong to that genus. They commented that Sesarmops intermedius (De Haan, 1835), S. sinensis (H. Milne Edwards, 1853) Chiromantes dehaani (H. Milne Edwards, 1853) and some species of Pseudosesarma Serène and Soh, 1970 were actually closer to each other than with genera they had been placed with, and the generic system of these species need to be revised (Ng et al. 2008: 223).

Three species of the two genera have been recorded from Taiwan: the widely distributed Bresedium brevipes (De Man, 1889), Sesarmops impressus H. Milne Edwards, 1837 and Sesarmops intermedius (De Haan, 1835) (see Ng et al. 2017). Three species have previously been recorded from the Philippines: Sesarmops impressus H. Milne Edwards, 1837, Sesarmops mindanaoensis (Rathbun, 1914) and Bresedium philippinense (Rathbun, 1914), the latter two of which are only known from their type localities of Mindanao and Busuanga Islands, Palawan, respectively (Rathbun 1914).

The present study focuses on the taxonomy of a number of poorly known and new Bresedium and Sesarmops species collected from Taiwan and the Philippines. As part of this study, we describe a new species of Bresedium as well as a new species of Sesarmops, both of which can be distinguished from congeners by a suite of carapace, chelipedal, gonopodal and vulvar characters. The morphological differences are also supported by molecular evidence from the 16S rDNA and cytochrome c oxidase subunit I (COI), which have been used extensively for the taxonomy and phylogeny of crabs (Chu et al. 2015), including the Sesarmidae (e.g., Cannicci et al. 2017; Shahdadi et al. 2017 2018a b; Li et al. 2019; Shih et al. 2019). In order to describe these two species, we also had to clarify the identities of Sesarmops mindanaoensis and Bresedium philippinense, and the types of both species were examined. Bresedium philippinense is proved to be a junior synonym of Sesarma brevipes; Sesarmops mindanaoensis is a distinct taxon.

MATERIALS AND METHODS

Specimens examined were deposited in the Biodiversity Research Museum, Academia Sinica, Taipei, Taiwan (ASIZ); Zoological Collections of the Department of Life Science, National Chung Hsing University, Taichung, Taiwan (NCHUZOOL); Naturalis Biodiversity Centre (previously the Rijksmuseum van Natuurlijke Historie), Leiden, The Netherlands (RMNH); U.S. National Museum of Natural History, Smithsonian Institution, Washington, D.C., U.S.A. (USNM); and Zoological Reference Collection of the Lee Kong Chian Natural History Museum, National University of Singapore (ZRC). Measurements provided are of the maximum carapace width (CW) and carapace length (CL) in millimetres. The abbreviations G1 and G2 are used for the male first and second gonopods, respectively. The abbreviations P2–P5 are used for the second to fifth pereiopods (first to fourth ambulatory legs), respectively. Measurements of ambulatory legs follow Maenosono and Naruse (2015). The terminology used follows Guinot et al. (2013) and Davie et al. (2015).

Sequences of the mitochondrial 16S rDNA and COI were obtained following the method described by Shih et al. (2016), after verification with the complimentary strand. Sequences of the different haplotypes have been deposited in the DNA Data Bank of Japan (DDBJ) (accession numbers in Table 1). Other species with similar morphology were included to confirm the phylogenetic relationships among related taxa (Table 1).

Table 1.

Haplotypes of 16S and COI genes of Sesarmidae specimens used in study. For abbreviations, see MATERIALS AND METHODS

Species	Locality	Sample size	Catalogue no. of NCHUZOOL (unless indicated)	Haplotype of 16S and COI	Access. no. of 16S	Access. no. of COI
Bresedium brevipes	Taiwan: Gangkou, Pingtung	1	15549	Bb1	LC537760	LC537802
	Philippines: Bohol	2	15555	Bb2	LC537761	LC537803
	Indonesia: Bali	1	15556	Bb3	LC537762	LC537804
	Australia: Queensland	1	ZRC 2009.0901	Bb4	LC537763	LC537805
Bresedium eurypleon n. sp.	Taiwan: Houwan, Pingtung	1	15557	Be1	LC537764	LC537806
	Taiwan: Houwan, Pingtung	1	15558	Be2	LC537765	LC537807
	Taiwan: Houwan, Pingtung	1	15831	Be3	LC537766	LC537808
	Philippines: Guimaras I.	1	ZRC 2017.0478a	Be4	LC537767	LC537809
Chiromantes dehaani	Japan: Bonin Islands	1	ZRC 2013.0173 (paratype of C. magnus)	Cd1	LC537768	LC537810
	Japan: Kagoshima	1	ZRC 2012.0057	Cd2	LC537769	LC537811
	Japan: Kumejima, Ryukyus	1	ZRC	Cd3	LC537770	LC537812
	Japan: Ishigaki, Ryukyus	1	15563	Cd4	LC537771	LC537813
	Taiwan: Wunliao, Taichung	1	15566	Cd5	LC500752	LC500772
	Taiwan: Wunliao, Taichung	1	15561	Cd6	LC500752	LC500771
	Taiwan: Gaomei, Taichung	1	15565	Cd7	LC500753	LC500773
	China: Shanghai	1	ZRC 2010.420 (as C. neglectum)	Cd8	LC537772	LC537814
	China: Guangzhou, Guangdong	1	15564	Cd9	LC500752	LC500774
Pseudosesarma bocourti	Malaysia: Tioman	1	15866	Pb	LC537773	LC537815
Pseudosesarma crassimanum	purchased	2	15867	Pc	LC537774	LC537816
Pseudosesarma edwardsii	Malaysia: Langkawi	1	16332	Pe1	LC537775	LC537817
	Singapore	1	ZRC 2003.0084	Pe2	LC537776	LC537818
Pseudosesarma patshuni	China: Yangjiang, Guangdong	1	15740	Pp	LC500765	LC500790
Sesarmops impressum 1	Madagascar: Mosoala Peninsula; Mayotte	2	ZRC 2010.0302; ZRC 2011.0005	Sim1	LC537777	LC537819
	Madagascar	1	MNHN.IV.2019.4522	Sim2	LC537778	LC537820
	Mayotte	1	MNHN.IV.2009.953	Sim3	LC537779	LC537821
Sesarmops impressum 2	Taiwan: Hualien	1	15868	Sima1	LC537780	LC537822
	Taiwan: Lanyu, Taitung	1	15869	Sima2	LC537781	LC537823
	Taiwan: Gangkou, Pingtung	1	15870	Sima2	LC537782	LC537824
	Philippines: Guimaras	1	ZRC 2017.0477	Sima3	LC537783	LC537825
	Philippines: Camiguin	1	15871	Sima4	LC537784	LC537826
	Philippines: unknown locality	1	ASIZ	Sima5	LC537785	LC537827
	Indonesia: Sulawesi	1	ZRC 2016.0252	Sima6	LC537786	LC537828
Sesarmops intermedius	Japan: Kyushu	1	ZRC 2013.0140	Sin1	LC537787	LC537829
	Japan: Amami, Ryukyus	1	15873	Sin2	LC537788	LC537830
	Japan: Kumejima, Ryukyus	1	ZRC	Sin3	LC500766	LC500791
	Japan: Kumejima, Ryukyus	1	ZRC	Sin4	LC537789	LC537831
	Japan: Iriomote, Ryukyus	1	15741	Sin3	LC500766	LC500791
	Taiwan: Aodi, New Taipei City	1	15872	Sin5	LC537790	LC537832
	Taiwan: Hualien	1	15742	Sin6	LC500766	LC500791
	Taiwan: Houwan, Pingtung	1	15743	Sin3	LC500766	LC500792
	Taiwan: Gangkou, Pingtung	2	15874	Sin3	LC537791	LC537833
	China: Shanghai	1	ZRC 2010.0421 (id. as S. sinensis)	Sin7	LC537792	LC537834
	China: Linhai, Zhejiang	1	15676 (id. as S. sinensis)	Sin7	LC537793	LC537835
	China: Xiapu, Fujian	1	15875 (id. as S. sinensis)	Sin8	LC537794	LC537836
Sesarmops mindanaoensis	Taiwan: Gangkou, Pingtung	1	15858	Smi	LC537795	LC537837
	Philippines: Kawasan, Cebu	1	16333	Smi	LC537796	LC537838
	Philippines: Kawasan, Cebu	1	ZRC 2019.1657	Smi	LC537797	LC537839
	Taiwan: Gangkou, Pingtung	1	15858	Smi	LC537798	LC537840
Sesarmops mora n. sp.	Taiwan: Gangkou, Pingtung	1	15865	Smo1	LC537799	LC537841
	Philippines: Cebu	1	ZRC 2012.0434	Smo2	LC537800	LC537842
	Philippines: Cebu	1	ASIZ	Smo1	LC537801	LC537843
Total		53

For the combined 16S and COI dataset, the best-fitting models for sequence evolution of individual datasets were determined by PartitionFinder (vers. 2.1.1, Lanfear et al. 2017), selected by the Bayesian information criterion (BIC). The best models obtained were both GTR+I+G and were subsequently applied to the partitioned Bayesian inference (BI) analysis. The BI was performed with MrBayes (vers. 3.2.6, Ronquist et al. 2012). The search was run with 4 chains for 10 million generations and 4 independent runs, with trees sampled every 1000 generations. The convergence of chains was determined by the average standard deviation of split frequency values below the recommended 0.01 (Ronquist et al. 2005) and the first 1100 trees were discarded as burnin. The maximum likelihood (ML) analysis was conducted in RAxML (vers. 7.2.6, Stamatakis 2006). The model GTR + G (i.e., GTRGAMMA) was used with 100 runs; the best ML tree was found by comparing the likelihood scores. The robustness of the ML tree was evaluated by 1,000 bootstrap pseudoreplicates under the model GTRGAMMA.

RESULTS

TAXONOMY

Sesarmidae Dana, 1851

Bresedium Serène and Soh, 1970

Type species: Sesarma edwardsii brevipes De Man, 1889, by original designation.

Remarks: Bresedium Serène and Soh, 1970, was established with Sesarma edwardsii brevipes De Man, 1889, as the type species, and currently contains three taxa, viz. B. brevipes (De Man, 1889), B. philippinense (Rathbun, 1914), and B. sediliense (Tweedie, 1940). Members of the genus were characterised by Serène and Soh (1970) as having a carapace broader than long and not prominently inflated, the lateral margin has two epibranchial teeth behind the external orbital tooth, the basal antennular article is at least twice as broad as long, the upper surface of the male palm is without distinct pectinated crest(s), the inner surface of the palm has a prominent vertical row of granules, the ambulatory legs are not elongated, the male telson is deeply inserted into the distal margin of pleonal somite 6, and the distal chitinous part of the G1 is elongate and slender. In many respects, Bresedium closely resembles members of Sesarmops, some species (notably S. impressus) which also possess a male telson which is inserted into the distal margin of pleonal somite 6 and possess an elongate distal chitinous part of the G1.

Of the three species, B. sediliense is easily distinguished by having the dactylus of the male cheliped as long as the height of palm, and the G1 distal chitinous process is relatively broad, shorter, and bent obliquely, with the tip just visible externally when the telson is closed (cf. Tweedie 1940; present material). On the other hand, B. brevipes has proportionately longer dactylar fingers (longer than height of the palm), with the distal chitinous process of the G1 is slender, relatively longer, straight, in line with the rest of the G1 and the tip is not distinctly bent and completely hidden by the closed telson. Serène and Soh (1970: 399) suspected B. philippinense was a species of Bresedium but could not be sure. Ng et al. (2008: 223) confirmed that it belonged to the genus and treated it as a distinct species. Bresedium brevipes and B. philippinense are very similar and their taxonomy has been unclear, mainly because the type of B. philippinense was only briefly described and has never been figured. The re-examination of the type male of B. philippinense as well as a good series of specimens from the Philippines now shows it is actually a junior synonym of B. brevipes. Bresedium sediliense (Tweedie, 1940) from Peninsular Malaysia is distinct from the other two species in that the dactylus of the chela is as long as the height of the palm (Tweedie 1940: 8b) and the elongate chitinous distal part of the G1 is inserted at an angle to the main shaft (Tweedie 1940: 8b). Bresedium brevipes (and B. philippinense) has the dactylus of the chela longer than the height of the palm (Figs. 2F, 3G) and the chitinous distal part of the G1 is proportionately longer and continues in a straight line with the main shaft (Figs. 5, 6E–K). The present paper will only deal with the taxonomy of Bresedium brevipes and B. philippinense as only they are present in Taiwan and the Philippines. The taxonomy of B. sediliense will be discussed in greater depth by CD Schubart and PKL Ng in an ongoing revision of these and other genera.

Bresedium brevipes (De Man, 1889)

(Figs. 1–6)

Sesarma edwardsii – De Man 1887: 649; De Man 1888: 185 pl. 13 (1–4). (not Sesarma edwardsii De Man, 1888).

Sesarma edwardsii var. brevipes De Man, 1889: 425 (Sydney, Australia); De Man 1890: 94 (no locality); De Man 1892: 330 (Flores).

Sesarma edwardsii var. breviceps (sic) – Bürger 1893: 617 (Philippines).

Sesarma (Episesarma) edwardsi var. brevipes – De Man 1895: 173 (Atjeh, Sumatra, Indonesia).

Sesarma (Sesarma s. s.) edwardsi var. brevipes – De Man 1902: 509 (Ternate, Batjan, Halmahera, Indonesia).

Sesarma (Sesarma s. s.) edwardsi philippinense Rathbun, 1914: 76 (Busuanga Island, Philippines); Tesch 1917: 148 (list).

Sesarma (Sesarma s. s.) edwardsii brevipes – Tesch 1917: 147 (Batjan, Indonesia).

Sesarma (Sesarma) brevipes – Serène 1968: 105 (list).

Sesarma (Sesarma) brevipes philippinensis – Serène 1968: 105 (list).

Bresedium brevipes – Serène and Soh 1970: 399 (taxonomy); Davie 2002: 220 (list); Ng et al. 2008: 220 (list); Koller et al. 2010: 366 (Taiwan); Li and Chiu 2013: 38, 3 unnumbered figs (Taiwan); Li and Chiu 2019a: 14, 2 unnumbered figs. (Taiwan); Li and Chiu 2019b: 58, 3 unnumbered figs (Taiwan).

Bresedium philippinensis – Serène and Soh 1970: 399 (discussion).

Bresedium philippinense – Ng et al. 2008: 220 (list).

Fig. 1.

Bresedium brevipes (De Man, 1889), in situ photographs in Taiwan. A, male (specimen not collected), Gangkou R. downstream, south bank, Pingtung, 13 January 2011; B, female (18.0 × 15.5 mm) (NCHUZOOL 16329), Gangkou R. downstream, south bank, Pingtung; C, male (17.9 × 15.5 mm) (ZRC 2019.1646), Gangzai R. estuary north bank, Pingtung; D, female (specimen not collected), Gangkou R. estuary, north bank, Pingtung, 4 July 2011; E, male (specimen not collected), Gangkou R. estuary, north bank, Pingtung, 13 July 2014; F, female (specimen not collected), Gangkou R. downstream, south bank, Pingtung, 13 January 2011.

Material examined: Holotype (Sesarma (Sesarma) edwardsi philippinense Rathbun, 1914), male (16.7 × 14.5) (USNM 45750), Pangauran R., Busuanga Island, Palawan, Philippines.

Others: Australia: 2 females (16.8 × 14.8, 15.3 × 13.3) (RMNH D1210), “Australia, New South Wales, Sydney”, coll. Museum Godeffroy; 2 males (25.0 × 21.8, 24.0 × 21.3) (ZRC 2009.0901), Flame Tree Creek, between Arlie Beach and Shute Harbour, Brisbane, Queensland, coll. J. W. Shaif and A. Humpherys, 2 June 1997. Philippines: Kawasan, Cebu: 8 males (18.4 × 15.5, 17.3 × 15.3, 15.9 × 13.4, 15.0 × 12.8, 15.7 × 13.8, 13.7 × 11.8, 13.5 × 11.7, 11.4 × 10.0), 2 females (21.1 × 17.7, 14.5 × 13.0) (ASIZ 1125), coll. H.-C. Liu, 25 November 2001; 13 males (largest 24.7 × 21.0), 1 ovigerous female (19.7 × 16.8), 7 females (ZRC 2019.1667), coll. P. K. L. Ng, 4 December 2001; 4 males (20.0 × 16.7, 18.4 × 15.7, 15.8 × 13.4, 12.6 × 11.2), 4 females (22.0 × 18.8, 16.3 × 13.8, 15.3 × 13.3, 10.9 × 9.2) (ASIZ 1204), coll. H.-C. Liu, 4 December 2001; 5 males (25.7 × 21.9, 25.6 × 21.7, 24.4 × 21.3, 25.1 × 21.5, 22.6 × 19.3) (ZRC 2016.0667), coll. N. K. Ng et al., 2 January 2002; 4 females (12.7 × 11.0, 11.2 × 9.3, 11.8 × 10.1, 9.8 × 8.4) (ASIZ), coll. H.-C. Liu, 15 February 2003; Loboc R., Bohol: 3 males (16.4 × 14.0, 17.4 × 14.9, 18.9 × 15.7), 3 females (12.2 × 9.7, 15.6 × 13.4, 17.3 × 15.0), 2 ovigerous females (14.3 × 12.1, 17.9 × 17.6), NCHUZOOL 15555, coll. 26 September 2003. Taiwan: Gangkou R. estuary, Pingtung: 1 female (13.9 × 12.0) (ZRC 2019.1644), coll. J.-J. Li, 13 July 2012; 1 female (16.9 × 14.3) (ZRC 2019.1643), coll. J.-J. Li, 15 July 2012; 1 male (17.3 × 14.9), 1 female (16.3 × 13.3) (NCHUZOOL 16325), coll. J.-J. Li, 10 October 2014; 1 female (14.1 × 12.3) (ZRC 2019.1645), coll. J.-J. Li, 24 September 2015; 1 female (14.9 × 12.7) (ZRC 2019.1642), coll. J.-J. Li, 9 December 2015; 1 female (15.3 × 13.3) (NCHUZOOL 16320), coll. J.-J. Li, 20 June 2016; 1 female (20.0 × 16.8) (NCHUZOOL 16323), coll. J.-J. Li, 22 June 2016; 1 male (21.7 × 19.5) (NCHUZOOL 15549), 2 males (22.4 × 19.5, 22.0 × 19.0), 1 female (19.3 × 16.7) (NCHUZOOL 16324), 2 females (21.0 × 17.7, 19.6 × 16.5) (NCHUZOOL 16326), 1 male (21.1 × 17.8), 1 female (24.6 × 21.7) (ZRC 2019.1641), coll. J.-J. Li, 18 May 2017; 2 males (22.3 × 18.9, 20.2 × 18.4), 1 female (20.5 × 17.8) (NCHUZOOL 16318), coll. J.-J. Li, 5 June 2017; 1 male (20.7 × 17.9), 1 female (21.0 × 18.3) (NCHUZOOL 16322), coll. J.-J. Li, 6 July 2017; 1 male (13.5 × 11.9) (NCHUZOOL 16321), coll. J.-J. Li, 7 July 2017; 1 male (18.8 × 16.3) (NCHUZOOL 16319), coll. J.-J. Li, 17 July 2017; 4 males (23.8 × 21.2, 20.9 × 18.7, 19.6 × 17.4, 19.4 × 17.3), 3 females (21.9 × 18.5, 17.4 × 14.8, 15.8 × 13.8) (NCHUZOOL 16327), 2 females (21.6 × 18.9, 16.3 × 14.0) (ZRC 2019.1651), coll. J.-J. Li, 11 August 2017; 4 males (23.5 × 20.3, 21.9 × 19.6, 20.5 × 18.5, 17.3 × 15.2), 4 females (28.4 × 27.5, 27.2 × 26.9, 19.8 × 17.3, 17.7 × 15.1) (NCHUZOOL 16328), coll. J.-J. Li, 30 October 2017; 1 female (19.3 × 17.4) (NCHUZOOL 16317), coll. J.-J. Li, 20 April 2018; Gangzai R. estuary, Pingtung: 1 male (17.9 × 15.5) (ZRC 2019.1646), coll. J.-J. Li, 16 June 2012; Meilun R. estuary, Hualien: 2 males (21.4 × 18.4, 13.7 × 12.2) (ZRC 2008.0876), coll. H.-C. Liu, 2 December 2000; 1 female (14.7 × 13.2) (ZRC 2019.1648), coll. J.-J. Li, 28 July 2012; 1 male (13.7 × 11.4) (ZRC 2019.1649), 1 female (14.4 × 14.1) (ZRC 2019.1647), coll. J.-J. Li, 3 March 2015; 1 male (15.4 × 13.7) (ZRC 2019.1650), coll. J.-J. Li, 25 July 2015; 1 female (18.0 × 15.5) (NCHUZOOL 16329) coll. J.-J. Li, 3 August 2017. Indonesia: 1 male (22.2 × 19.1) (RMNH D1195), Batjan Island, Moluccas, coll. Kükenthal Expedition, 1893–94; 1 male (5.8 × 5.1) (NCHUZOOL 15556), Bali, Indonesia, coll. H.-T. Shih, 22 July 2014.

Diagnosis of male: Carapace (Figs. 2A, D, 4A, D, G) square in dorsal view, 1.1 ± 0.1 times broader than long (n = 14); regions well defined, separated by shallow grooves; postfrontal region distinct, separated into 4 lobes by deep grooves; front deflexed downwards, margin distinctly concave in dorsal view. Anterolateral margin with large triangular, exorbital angle and smaller, triangular epibranchial tooth; lateral margin straight, slightly divergent posteriorly (Fig. 4A). Cornea reaching edge of external orbital tooth. Chelipeds (Figs. 2F, 3G, H) robust, outer surface with numerous rounded granules; dactylus dorsal margin with numerous chitinous granules; proximal part of fixed-finger slightly concave. Ambulatory legs (Figs. 4B, E, H, 6A–D) stout; P3 and P4 subequal, longer than others, about 1.4 ± 0.1 times carapace width (n = 14). P3 merus 2.2 ± 0.2 times as long as broad (n = 7); upper margin with acute subdistal spine. Propodus of P3 2.2 ± 0.2 times as long as broad (n = 7), with accessory stria on inferior proximal portion of outer surface, dorsal and ventral margins with short stiff setae. Dactylus of P3 0.6 ± 0.1 times length of propodus (n = 7), slightly curved, terminating in acute calcareous tip; dorsal and ventral margins with short stiff setae. Pleon (Figs. 2B, C, 4C, F, I) relatively broad, all somites free. Telson semicircular, evenly rounded, as long as preceding somite, base of telson deeply inserted in somite 6. G1 (Figs. 5, 6E–K) straight, apical part chitinous, forming elongate slim process, bent at an angle of 35o–45o, ending in truncate tip.

Fig. 2.

Bresedium brevipes (De Man, 1889), life colouration. A, B, male (20.5 × 17.8 mm) (NCHUZOOL 16318), Gangkou R., Taiwan; C, male (17.9 × 15.5 mm) (ZRC 2019.1646), Gangzai R., Taiwan; D–F, male (25.1 × 21.5 mm) (ZRC 2016.0667), Kawasan, Cebu, Philippines. A, D, overall dorsal view; B, C, ventral view of cephalothorax; E, frontal view of cephalothorax; F, outer view of left chela.

Fig. 3.

Bresedium brevipes (De Man, 1889). A, female (15.3 × 13.3 mm) (RMNH D1210), “Sydney”, Australia; B, D, male (25.0 × 21.8 mm, 24.0 × 21.3 mm) (ZRC 2009.0901), Brisbane, Australia; C, E, F, male (16.7 × 14.5 mm) (USNM 45750) (holotype of Sesarma (Sesarma) edwardsi philippinense Rathbun, 1914), Philippines; G, H, male (17.9 × 15.5 mm) (ZRC 2019.1646), Gangzai R., Taiwan; I, female (14.1 × 12.3 mm) (ZRC 2019.1645), Gangzai R., Taiwan. A–C, overall dorsal view; E, dorsal view of carapace; D, F, ventral view of anterior thoracic sternum and pleon; G, I, outer view of left chela; H, dorsal view of left chela.

Fig. 4.

Bresedium brevipes (De Man, 1889). A–C, male (22.2 × 19.1 mm) (RMNH D1195), Batjan Island, Indonesia; D–F, male (21.3 × 18.5 mm) (ZRC 2019.1667), Taiwan; G–I, male (24.7 × 21.0 mm) (ZRC), Philippines. A, D, G, right side of carapace; B, E, H, left third ambulatory leg; C, male pleonal somites 3–6 and telon; D, E, male pleonal somites 5, 6 and telson. Scale bars = 1.0 mm.

Fig. 5.

Bresedium brevipes (De Man, 1889). A–D, male (22.2 × 19.1 mm) (RMNH D1195), Batjan Island, Indonesia, right G1; E, F, male (21.3 × 18.5 mm) (ZRC), Taiwan, left G1; G, H, male (24.7 × 21.0 mm) (ZRC), Philippines, left G1. A, F, H, dorsal view; B, E, G, ventral view; C, D, distal part of G1. Scale bars = 1.0 mm.

Fig. 6.

Bresedium brevipes (De Man, 1889). A–C, B. brevipes; D, Sesarma (Sesarma) edwardsi philippinense, holotype. A, male (22.0 × 19.0 mm) (NCHUZOOL 16324), Taiwan; B, male (22.3 × 18.9 mm) (NCHUZOOL 16318), Taiwan; C, male (19.3 × 17.4 mm) (NCHUZOOL 16319), Taiwan; D, male (16.7 × 14.5 mm) (USNM 45750) (holotype of Sesarma (Sesarma) edwardsi philippinense Rathbun, 1914), Philippines; E, male (20.7 × 17.9) (NCHUZOOL 16322), Taiwan; F–J, males 25.6 × 21.7 mm, 22.6 × 19.3 mm, 25.7 × 21.9 mm, 24.4 × 21.3 mm, 25.1 × 21.5 mm) (ZRC 2016.0667), respectively, Philippines; K, male (24.9 × 21.8) (ZRC 2009.0901), Australia; L, female (16.9 × 14.3 mm) (ZRC 2019.1643), Taiwan; M, ovigerous female (19.7 × 16.8 mm) (ZRC 2019.1667), Philippines. A–D, right side of carapace and P3; E–K, left G1s; L, M, vulvae.

Female: Carapace broader than male, 1.1 ± 0.03 times broader than long (n = 10). Chelipeds smaller than male, the base-half dactylus dorsal margin with numerous granules. Pleon wide, rounded, telson semicircular, base partially inserted in somite 6. Vulva (Figs. 4J, 6L, M) not near anterior edge of sternite 5, operculum knob-like; posterior sternal vulvar cover rounded, not covering operculum.

Colouration in life: There is considerable variation in colour, with the carapace brown to pale purple, usually with the gastric region dark brown; the chelae being reddish-orange to reddish-purple, with the tips of the fingers sometimes yellow (Figs. 1, 2).

Ecology: This species can be found both on land (several meters away from water) and the muddy river bank in habitats typically about 250 m to 500 m away from sea. It has been found sympatrically with more terrestrial sesarmids Geosesarma hednon Ng, Liu and Schubart, 2003 (Kenting, Pingtuing, Taiwan and Kawasan, Cebu, Philippines) and Sesarmops weberi (De Man, 1892) (Kawasan). Along the river banks, it has been collected with Sesarmops mora n. sp. (Kenting and Kawasan) and Parasesarma dumacense (Rathbun, 1914) (Kawasan).

Remarks: De Man (1889) described Sesarma edwardsii var. brevipes from one male and two female specimens from Sydney, Australia. Measurements of one male (13.7 × 12.0 mm) and one female (13.8 × 12.3 mm) were provided. He also cited two of his earlier papers (De Man 1887 1888) where he described Sesarma edwardsii from Bengal seas and Mergui, but this was probably done with reference to the nominate species as he had regarded the Australian specimens as only a new variety. De Man (1890 1892 1895 1902) subsequently recorded this species from Sumatra, Flores and Moluccas. The real Sesarma edwardsii De Man, 1887 is a distinct species and is the type species of Pseudosesarma Serène and Soh, 1970 (see Ng and Schubart 2017). Noteworthy also is that in both B. brevipes (and B. philippinense), the outer margins of the ambulatory carpus and propodus are densely lined with short black setae, absent in P. edwardsii s. str. (cf. Ng and Schubart 2017).

Rathbun (1914: 76) described Sesarma (Sesarma) edwardsi philippinense from three males and three females from Busuanga Island in the Philippines and noted that “Variety brevipes de Man has a male pleon similar to that of philippinense, but has much shorter legs. The legs of the Philippine form are as in typical edwardsi” (Rathbun 1914: 76). The holotype female of Bresedium philippinense (Rathbun, 1914) is similar to specimens of B. brevipes in general morphology. Only minor diagnostic characters were provided in the original description by Rathbun (1914), who noted that the chelae of B. philippinense are narrower, the fingers are more elongate and more horizontal. Serène and Soh (1970: 399) commented that this taxon is probably a species of Bresedium and Ng et al. (2008) agreed.

De Man’s (1889) types of S. brevipes from “Sydney” are neither in the Senckenberg Museum or Naturalis (see Fransen et al. 1997). Davie (2002) commented that the types may be in the Amsterdam Museum. The Amsterdam Museum material has now been integrated with Naturalis collection (denoted still by its code of ZMA), but we have not been able to find these “Sydney” specimens there as well. In the Naturalis, however, there are two female specimens catalogued under RMNH D1210 from “Australia, New South Wales, Sydney” which had been donated from the Museum Godeffroy. The data associated with these two specimens is: “Topotype. Don. Museum Godeffroy, no. 16330 (error for 16300?). This material was described by De Man (1890: 94) under the above name, but was said to be from an unknown locality. Tesch (1917: 147–148) also referred to this lot and to De Man, 1890, noting that it was from an unknown locality. However, the sample has a handwritten number 16330. In Catalog viii of Museum Godeffroy (Schmeltz 1881: 14, 15), it is listed on p. 14: “16300 Sesarma sp.? Sidney”. This material is mentioned by De Man (1890), but he says the provenance of the specimen was not known, though he provided measurements for the larger female (16.8 × 14.8 mm). Interestingly, indications are that both these specimens are from Sydney in Australia as well, as clearly indicated by Schmeltz (1881: 14) in the above-mentioned catalogue of the Godeffroy Museum collections (see Bieler and Petit 2012, for details). Based on this information, these two female specimens cannot be the original syntypes of De Man (1889) (both female specimens are larger than his original female measured), and were only examined later. The original material of De Man (1889) therefore appears to be lost. Nevertheless, the RMNH specimens (Fig. 3A) and fresher ones from Brisbane (Fig. 3B) match the original descriptions and figures by De Man (1889) very well. The species is not known from further south in Sydney, which is probably too cold for the species in winter, and the original location is almost certainly incorrect (Davie 2002: 220). The six type specimens of Bresedium philippinense (Rathbun, 1914) are all in the USNM. Rathbun (1914) selected one male 16.7 mm in carapace length as the holotype, and this was examined for this study (Fig. 3C, E, F).

After comparing the good series of specimens from Australia (Brisbane), Indonesia (Moluccas), Philippines (Kawasan, Cebu) and Taiwan (Hengchun Peninsula), supported by molecular evidence, we are confident Bresedium philippinense is a junior synonym of B. brevipes. There is significant variation in the proportion of the ambulatory legs, and other characters of the anterolateral margin and the angle of G1 tip (Figs. 4A, D, G, 5, 6E–K).

The third ambulatory leg of the specimens of B. brevipes from Australia and Indonesia agree in general with that illustrated by De Man (1889: pl. 9(6b)), especially in the width of the merus (Fig. 4B). On the other hand, the P3 merus of most of the present Philippine specimens are proportionately more slender and seem to agree better with the type and what was described by Rathbun (1914) for B. philippinense (Fig. 4H). Based on the measurement of 68 B. brevipes specimens (20 from the Philippines and 48 from Taiwan), the ratios of CW/P3 are 1.31–1.77 (average 1.56), in comparison, the ratios of CW/P3 are 1.49 in B. philippinense holotype, which is within the range (1.31–1.77) of CW/P3 in B. brevipes. The leg (notably the width of the merus) is variable and therefore is not a reliable character to separate the species. The Taiwanese specimens in particular, have leg meri which vary from distinctly broad to more slender (Figs. 4E, 6A– C). The G1 structures of the Australian, Indonesian and Taiwanese specimens differ from most of the Philippine specimens in that the elongated chitinous part is slightly more bent and the tip is usually bifurcated (Fig. 5A– F). Those of the Philippine specimens tend to have the chitinous part almost straight with the rest of the G1 and the tip is rounded (Fig. 5G, H). The specimens from the various sites, however, show that the variation is substantial and there are many intermediate states (Figs. 5, 6E–K). As such, we do not believe the G1 differences observed are reliable. Comparing some of the larger specimens, we also find that the carapace of those from the Philippines is usually more setose, being uniformly covered with numerous tufts of short setae (vs. scattered short setae mainly on anterior surface in specimens from Australia and occasionally Taiwan); the ambulatory dactylus has slightly more short setae (Fig. 2D vs. Figs. 2A, 3A-C); the median part of the male pleon has a pair of short, black stiff setae, with the margins of the telson having more of the same kind of setae (vs. may be indistinct) (Fig. 4C, F vs. Fig. 4I). That being said, when specimens of various sizes are compared, these characters vary enough to make them unreliable. As a result, we believe both species are synonymous. This is also supported by the available genetic data (Fig. 22).

Bresedium eurypleon n. sp.

(Figs. 7–10)

urn:lsid:zoobank.org:act:830368D5-74B1-4B1F-8436-F5ABF22F0063

Bresedium philippinensis – Liu 2016: 7, 20, 24, 33, 65, fig. 3-1.1 (Pingtung, Taiwan). (not Sesarma (Sesarma) edwardsi philippinense Rathbun, 1914)

Material examined: Holotype: male (17.9 × 14.8) (NCHUZOOL 16316), Houwan forest, Pingtung, Taiwan, coll. J.-J. Li, 8 May 2019. Paratypes: Taiwan: 1 female (19.6 × 16.7) (NCHUZOOL 16379), 1 ovigerous female (19.9 × 17.1) (larvae released) (NCHUZOOL 16331), Houwan beach, Pingtung, coll. H.-D. Yang, 15 August 2015; 1 female (18.9 × 15.8) (ZRC 2019.1652), Gangkou R. estuary, Pingtung; 1 female (15.6 × 13.4), NCHUZOOL 15557, Houwan, Pingtung, coll. M.-Z. Wu and C.-Y. Chi, 1 October 2016; 1 female (20.5 × 17.6) (NCHUZOOL 15558), Houwan, Pingtung, P.-Y. Hsu et al., 21 July 2017; 1 female (18.8 × 15.0) (NCHUZOOL 16316), Nioushan, Hualien, coll. P.-H. Ho, 12 June 2016. Others: Philippines: 1 male (20.9 × 19.2) (ZRC 2017.0478a), 3 males (19.6 × 16.1, 17.6 × 14.4, 17.5 × 14.4) (ZRC 2017.0478b), Jordan, Guimaras Island, coll. J. C. E. Mendoza, 1 June 2017. Indonesia: 1 male (26.2 × 22.7) (ZRC 2019.1660), Manado Murex Resort, North Sulawesi, coll. P. K. L. Ng et al., 17 July 2013.

Comparative material: Bresedium sediliense (Tweedie, 1940): Malaysia: Johor: 37 males (largest 21.2 × 18.2 mm), 22 females (largest 20.3 × 17.8 mm) (ZRC 1965.7.29.121–133) [paratypes of Sesarma sediliensis Tweedie, 1940], Sedili River, coll. M. W. F. Tweedie, March 1938. Sarawak: 19 males (largest 20.1 × 17.9 mm), 17 females (largest 19.2 × 16.7 mm, 2 ovigerous) (ZRC 1972.3.7.25–35), water ditch, Kuching, coll. M. W. F. Tweedie, January 1949.

Diagnosis of male: Carapace (Figs. 7A, F, 8A, 10A) almost rectangular in dorsal view, 1.2 ± 2.0 times broader than long (n = 5); regions well defined, separated by shallow grooves; postfrontal region distinct, separated into 4 lobes by deep grooves; front deflexed downwards, margin distinctly concave in dorsal view. Anterolateral margin with large triangular, exorbital angle and smaller, triangular epibranchial tooth; lateral margin straight, slightly divergent posteriorly. Cornea reaching edge of external orbital tooth. Chelipeds (Figs. 7C, H, 8C, D) robust, outer surface with numerous rounded granules; dactylus dorsal margin with numerous chitinous granules; proximal part of fixed-finger slightly concave. Ambulatory legs (Figs. 7A, 8A) stout; P3 and P4 subequal, longer than others, about 2.1 ± 0.1 times carapace width (n = 5). P3 merus 2.0 ± 0.1 times as long as broad (n = 5); upper margin with acute subdistal spine. Propodus of P3 2.5 ± 0.1 times as long as broad (n = 5), with accessory stria on inferior proximal portion of outer surface, dorsal and ventral margins with short stiff setae. Dactylus of P3 0.9 ± 0.1 times length of propodus (n = 5), slightly curved, terminating in acute calcareous tip; dorsal and ventral margins with short stiff setae. Pleon (Figs. 7B, 8B) relatively broad, all somites free. Telson semicircular, evenly rounded, as long as preceding somite, base of telson deeply inserted in somite 6. G1 (Figs. 8G, H, 10B, C) straight, apical part chitinous, forming elongate slim process, bent at an angle of about 55o, ending in truncate tip.

Fig. 7.

Bresedium eurypleon n. sp., colour in life. A–C, holotype male (17.9 × 14.8 mm) (NCHUZOOL 16316), Taiwan; D, paratype female (18.9 × 15.8 mm) (ZRC 2019.1652), Taiwan; E–H, male (26.2 × 22.7 mm) (ZRC 2019.1660), Sulawesi. A, D, E, F, overall dorsal view; B, ventral view of cephalothorax; C, outer view of chelae; G, frontal view of cephalothorax; H, outer view of left chela.

Fig. 8.

Bresedium eurypleon n. sp. A, B, male (20.9 × 19.2 mm) (ZRC 2017.0478a), Philippines; C, D, G, H, Taiwan, holotype male (17.9 × 14.8 mm) (NCHUZOOL 16316), Taiwan; E, F, paratype female (18.9 × 15.8 mm) (ZRC 2019.1652), Taiwan. A, dorsal view; B, ventral view; C–E, left palms; F, vulvae; G, H, left G1.

Fig. 9.

Bresedium eurypleon n. sp., dorsal view of carapace. A, paratype female (18.9 × 15.8 mm) (ZRC 2019.1652), Kangkou River, Taiwan; B, paratype female (20.6 × 16.6 mm) (NCHUZOOL 16331), Houwan, Pingtung, Taiwan; C, paratype female (18.8 × 15.0 mm) (NCHUZOOL 16316), Nioushan, Hualien, Taiwan.

Fig. 10.

Bresedium eurypleon n. sp. A–C, male (20.9 × 19.2 mm) (ZRC 2017.0478a), Philippines; D, paratype female (18.8 × 15.0 mm) (NCHUZOOL 16316), Taiwan. A, left side of carapace; B, left G1; C, distal part of lef G1; D, left female vulva. Scale bars = 1.0 mm.

Female: Carapace (Figs. 7D, 9) broader than male, 1.2 ± 0.6 times broader than long (n = 3). Chelipeds smaller than male, the base-half dactylus dorsal margin with numerous granules. Pleon wide, rounded, telson semicircular, base partially inserted in somite 6. Vulva (Figs. 8F, 10D) near anterior edge of sternite 5, operculum knob-like; posterior sternal vulvar cover triangular, elongate, covering operculum in ventral view.

Etymology: The name is derived from the Greek “eury” and “pleon” for wide and male pleon, respectively; alluding to the proportionately wider structure of the species. The name is used as a noun.

Colouration in life: Carapace and legs brown, with or without some speckles; chelipeds evenly reddish purple (Fig. 7).

Distribution: Taiwan (Hualien and Pingtung), Philippines (Guimaras Island) and Indonesia (Sulawesi).

Ecology: Three females were found to release larvae into the sea during high tide of full moon night in August 2015 (Liu 2016; JJ Li, personal observation). Another non-ovigerous female was found on a muddy bank of the lower reaches of a small stream river in Niousha, Hualien, Taiwan.

Remarks: Male B. eurypleon n. sp. can easily be distinguished from adult male B. brevipes by its relatively broader and more trapezoidal-shaped carapace (Figs. 7A, D, F, 8A, 9) (narrower, square-shaped carapace in B. brevipes; Figs. 2A, D, 3A–C); the relatively smaller granules on the outer surface of the palm (Fig. 8C, E) (relatively larger in B. brevipes; Figs. 2F, 3G); distinctly wider male sixth pleonal somite (Fig. 7B) (proportionately narrower in B. brevipes; Figs. 2B, C, 3D, F); and the relatively more elongated and bent male G1 tip (Fig. 8G, H) (shorter and almost in line with the stem in B. brevipes; Figs. 5, 6E–K). The vulvae are different in the two species, with the posterior sternal vulvar cover triangular and more elongate, covering the operculum in B. eurypleon (Figs. 8F, 10D) whereas in B. brevipes, the posterior sternal vulvar cover is rounded and the operculum is clearly exposed (Figs. 4J, 6L, M).

The carapace shape slightly varies in females, with one specimen from southern Taiwan being more broadly trapezoidal (ZRC 2019.1652) (Fig. 9A) compared to those from other parts of the island (Fig. 9B, C). This is regarded as intraspecific variation and supported by the genetic data (Fig. 22).

In life, adults of both species show similar colouration of carapace and legs, with large males of B. brevipes often possessing purple palms with finger tips yellow (Fig. 2B, F), with medium-sized and small males with light brownish red palms and orange fingers (Fig. 2C). Some specimens, however, have the entire chela purple (Fig. 2F). All specimens of B. eurypleon examined, however, always have purple palms and fingers, with the tip pale but not distinctly yellow (Fig. 7C, H).

Sesarmops Serène and Soh, 1970

Type species: Sesarma impressa H. Milne Edwards, 1837, by original designation.

Remarks: Serène and Soh (1970: 401) recognised five species in Sesarmops: S. atrorubens (Hess, 1865), S. impressus (H. Milne Edwards, 1837), S. intermedius (De Haan, 1835), S. mindanaoensis (Rathbun, 1914), and S. sinensis (H. Milne Edwards, 1853). Ng et al. (2008: 224) provisionally added Sesarma weberi (De Man, 1892) (from Flores) to Sesarmops. Sesarmops atrorubens is a poorly known species and was supposedly described from Sydney, Australia, by Hess (1865) and while it has also been reported from Timor, Ambon and Fiji (Tesch 1917: 131), its taxonomy is still unclear as it has never been described or figured to modern standards. Sesarmops mindanaoensis is also poorly known and was briefly described from one female from Mindanao, Philippines, and has never been figured.

As for the type species, S. impressus (type locality not known), Sesarma similis Hess, 1865 (type locality supposedly Sydney, Australia), and Sesarma frontale A. Milne-Edwards, 1869 (type locality Madagascar), both the latter are currently regarded as junior synonyms (see De Man, 1887: 649; De Man, 1902: 527; Tesch, 1917: 158). We have examined the available types or material of S. atrorubens, S. impressus, S. similis and S. frontale, and the taxonomy of these species is complex and will have to be treated at another time. In summary, however, we have examined the dried type female of S. impressus in the Muséum National d’Histoire naturelle, Paris, France (MNHN). It is from an unknown location. Sesarmops frontale (A. Milne-Edwards, 1869) was described from Madagascar and we have also examined the type specimens in MNHN and they are identical to the type female of S. impressus. Specimens which have been called “S. impressus” from the West Pacific are superficially similar to S. impressus s. str. (presumably also from the Indian Ocean) and S. frontale, but differ in details of the carapace and G1 structures. Their colours in life are also strikingly different, with those from the Indian Ocean possessing cream to yellow carapaces and cream chelae whereas West Pacific material has dark purplish brown to brown carapaces with purple chelae (unpublished data). A preliminary genetic study shows the Indian and Pacific Ocean population represent two non-sister clades (Table 1; Fig. 22) and clearly belong to two species. Until their taxonomy can be properly resolved, they are here treated as one species for the moment, i.e., as Sesarmops impressus s. lato. The authors examined fresh specimens of Sesarmops atrorubens and it is a good species, very different from other Sesarmops species with a very short stout G1 and other characters that argue against its inclusion in in the genus (unpublished data). As suggested by Hess (1865) himself, S. similis is likely to be junior synonym of S. atrorubens as it was only known from a female from the same area the latter was collected. The systematics of S. atrorubens and related species will be dealt with at another occasion by the authors and CD Schubart.

The present paper will only deal with two new species found in the Philippines and Taiwan; both are very distinct from S. atrorubens and S. impressus s. lato. Sesarmops mindanaoensis, however, is figured for the first time so that appropriate comparisons can be made with the new species.

Sesarmops is clearly polyphyletic and some of the species (e.g., S. atrorubens as discussed earlier), certainly do not belong there. Its affinity to Bresedium, as noted earlier, is also in question. Ng et al. (2008: 224) have already commented that S. intermedius and S. sinensis (from China, Taiwan and Japan) did not belong to the same clade as S. impressus and was actually closer to some species of Chiromantes Gistel, 1848 and Pseudosesarma Serène and Soh, 1970; S. weberi was probably allied with Labuanium trapezoideum (H. Milne Edwards, 1837) instead. Of the two new species recognised here, S. mora n. sp. is closer to S. impressus s. lato in general features and, while clearly different species, are likely to be congeneric (Fig. 22). Sesarmops mindanaoensis, however, although possessing a generally similar carapace as the other species, has a different thoracic sternum and male pleon, and is unlikely to be a Sesarmops species as indicated by the genetic analysis (Fig. 22). Pending a revision of Sesarmops, however, it is retained here for the moment.

Comparative material: Pseudosesarma edwardsii (De Man, 1887): 1 male (21.2 × 18.9), 1 female (16.9 × 15.4) (NCHUZOOL 16332), Langkawi, Peninsular Malaysia, coll. J.-J. Li, 19 December 2016 (see also Ng and Schubart 2017, for additional material). Pseudosesarma modestum (De Man, 1902): holotype male (25.0 × 20.9) (SMF 1989), Ternate, Moluccas, Indonesia, coll. W. Kükenthal, 26 December 1893–11 June 1894. Sesarmops impressus (H. Milne Edwards, 1837): 2 males (28.5 × 25.0, 23.4 × 27.6), 1 female (30.4 × 25.5) (ZRC 2009.0896), Mahi, Seychelles, coll. 2009; 1 male (37.6 × 32.1) (ZRC 2011.0005), station 9, Bassin Mro Oua Ouroveni, Mayotte, Comoros, coll. Tervuren Museum, 11 October 2000; 1 male (23.7 × 21.5) (ZRC 2015.0344), Bay of Bengal, South Andaman Islands, India, coll. I. Das, 20–30 August 1997; 1 female (36.7 × 34.8) (NCHUZOOL 15870), Gangkou R. estuary, Pingtung, Taiwan, 2 July 2001; 2 males (37.6 × 33.7, 35.4 × 32.3), 1 female (23.0 × 20.7) (NCHUZOOL 15069), lower reaches of Gangkou R. estuary, Pingtung, Taiwan, coll. J.-J. Li, 6 July 2017; 2 females (29.0 × 26.3, 28.9 × 26.8) (NCHUZOOL 15071), lower reaches of Gangkou R. estuary, Pingtung, Taiwan, coll. J.-J. Li, 18 May 2019; 1 male (35.2 × 34.6) (NCHUZOOL 15869), Lanyu, Taitung, Taiwan, 7 April 2002; 1 male (30.3 × 29.6) (NCHUZOOL 15868), Meilun R. estuary, Hualien, Taiwan, 29 July 2014; 2 males (larger 31.6 × 34.7) (ZRC 2017.0477), Guimaras I., Philippines, coll. J. C. E. Mendoza and L. Ganancial, 1 June 2017; 1 male (29.2 × 29.2) (NCHUZOOL 15871), Camiguin I., Philippines, coll. H.-T. Shih, 30 August 2003; 1 female (10.5 × 9.7) (ASIZ), Philippines, coll. H.-C. Liu, 15 February 2003.

Sesarmops mindanaoensis (Rathbun, 1914)

(Figs. 11A, B, 12–14)

Sesarma (Sesarma) mindanaoense Rathbun, 1914: 75.

Sesarmops mindanaoensis – Serène and Soh 1970: 401, 406; Ng et al. 2008: 223; Liu 2013: 32, fig. 2.

Material examined: Holotype female (19.6 × 18.2) (USNM 45765), small stream south side of Cotabato, Mindanao, Philippines, coll. 20 May 1908. Philippines: Kawasan, Cebu: 1 male (34.1 × 31.6), 1 female (35.6 × 32.4) (ZRC 2014.0285), coll. H.-C. Liu, 3 December 2001; 5 males (30.8 × 29.9, 30.7 × 28.7, 31.6 × 29.1, 24.1 × 21.8, 23.5 × 21.6), 2 females (33.7 × 30.7, 29.0 × 26.7) (ZRC 2019.1658), coll. P. K. L. Ng, 30 July 2003; 1 male (36.4 × 35.0) (ZRC 2019.1657), 1 male (31.2 × 31.3) (NCHUZOOL 16333), 2 females (27.9 × 26.4, 26.0 × 24.9) (ZRC 2019.1657), coll. J.-J. Li, 6 September 2018; Loboc R., Bohol: 1 male (24.1 × 23.5), 3 females (18.6 × 17.5, 18.1 × 16.9) (ASIZ 72948), 1 male (22.5 × 21.7), 1 female (18.8 × 17.8) (ZRC 2019.1110), 1 female (16.4 × 15.4) (ASIZ 72948), Philippines: Loboc R., Bohol, coll. H.-C. Liu et al., 19 February 2003. Taiwan: 1 female (25.6 × 23.3) (NCHUZOOL 16334), 1 female (24.8 × 23.5) (NCHUZOOL 15858), Gangkou R. estuary, Pingtung, coll. J.-J. Li, 18 May 2017.

Diagnosis of male: Carapace (Figs. 12A, E, 14A, B) nearly square in dorsal view, 1.0 ± 0.04 times broader than long (n = 4); regions well defined, separated by shallow grooves; postfrontal region distinct, separated into 4 lobes by deep grooves; front deflexed downwards, margin distinctly concave in dorsal view. Anterolateral margin with large triangular, exorbital angle and smaller, acutely triangular, epibranchial tooth; lateral margin straight, slightly divergent posteriorly. Cornea reaching edge of external orbital tooth. Chelipeds (Figs. 12F, G, 16C, D) robust, outer surface with numerous rounded granules, with a prominent line of tubercles along inner palm surface; dactylus curved, dorsal margin with numerous granules; proximal part of fixed-finger slightly concave, smooth. Ambulatory legs (Fig. 12A, E) slender; P3 and P4 subequal, longer than others, about 2.4 ± 0.1 times carapace width (n = 4). P3 merus 2.8 ± 0.1 times as long as broad (n = 4); upper margin with acute subdistal spine. Propodus of P3 3.0 ± 0.1 times as long as broad (n = 4), with accessory stria on inferior proximal portion of outer surface, dorsal and ventral margins with short stiff setae. Dactylus of P3 0.6 ± 0.1 times length of propodus (n = 4), slightly curved, terminating in acute calcareous tip; dorsal and ventral margins with short stiff setae. Pleon (Fig. 12B) relatively broad, all somites free. Telson semicircular, evenly rounded, as long as preceding somite, base of telson not inserted in somite 6. G1 (Figs. 16H, I, 17B, C) straight, relatively stout; apical process short, chitinous part short, ending in truncate tip; setae long, simple, originating at base of apical process. G2 shorter than quarter length of G1.

Fig. 11.

Life colouration. A, B, Sesarmops mindanaoensis (Rathbun, 1914), male (specimen not collected), Philippines; C, S. mora n. sp., holotype male (27.7 × 25.5 mm) (NCHUZOOL 16137), Taiwan; D, S. mora n. sp., paratype female (25.2 × 22.6 mm) (NCHUZOOL 16335), Taiwan.

Fig. 12.

Sesarmops mindanaoensis (Rathbun, 1914), colour in life. A, B, male (36.4 × 35.0 mm) (ZRC), Philippines; C, D, paratype female (24.8 × 23.5 mm) (NCHUZOOL 15858), Taiwan; E-G, male (30.8 × 29.9 mm) (ZRC 2019.1658), Philippines. A, C, E, overall dorsal view; B, D, ventral view of cephalothorax; F, frontal view of cephalothorax; G, outer view of left chela.

Fig. 13.

Sesarmops mindanaoensis (Rathbun, 1914), holotype female (19.6 × 18.2 mm) (USNM 45765), Philippines. A, overall dorsal view; B, dorsal view of carapace; C, frontal view of cephalothorax; D, left third maxilliped; E, outer view of left chela; F, left ambulatory legs; G, right ambulatory legs; H, pleon.

Fig. 14.

Sesarmops mindanaoensis (Rathbun, 1914), female (21.5 × 19.7 mm) (ZRC 2014.285), Philippines. A, overall dorsal view; B, dorsal view of carapace; C, frontal view of cephalothorax; D, outer view of right chela; E, left ambulatory legs; F, right ambulatory legs; G, pleon.

Female: Carapace (Figs. 12C, 13A, B, 15A) more convex and broader than male, 1.1 ± 0.4 times broader than long (n = 6). Chelipeds (Figs. 13E, 14D, 15C) smaller than male. P3 merus slightly stouter than male, 2.7 ± 0.1 times as long as broad (n = 6). Pleon (Figs. 13H, 14G, 15B) wide, rounded, telson semicircular, base partially inserted in somite 6. Vulva (Figs. 16G, 17D) near anterior edge of sternite 5, central operculum tubular, oval shaped, directed anteriorly; posterior and anterior sternal vulvar covers low.

Fig. 15.

A–F, Sesarmops mindanaoensis (Rathbun, 1914). A–F, female (18.8 × 17.8 mm) (ZRC 2019.1110), Philippines; G, H, male (22.5 × 21.7 mm) (ZRC 2019.1110), Philippines. D, right ambulatory legs; E, G, right P4 propodus and dactylus; F, H, right P5 propodus and dactylus.

Fig. 16.

Sesarmops mindanaoensis (Rathbun, 1914). A, C, D, I, H, male (36.4 × 35.0 mm) (ZRC), Philippines; B, E, F, G, female (24.8 × 23.5 mm) (NCHUZOOL 15858), Taiwan. A, B, frontal view of carapace; C, outer view of right chela; D, inner view of right chela; E, outer view of left chela; F, inner view of right chela; G, vulvae; H, I, left G1.

Fig. 17.

Sesarmops mindanaoensis (Rathbun, 1914), male (36.4 × 35.0 mm) (ZRC). A, carapace dorsal view; B, C, left G1; D, left vulvae. Scale bars = 1.0 mm.

Colouration in life: Carapace and legs dark or light brown, without prominent spots; male chelipeds purple or reddish purple, cornea greenish yellow (Figs. 11A, B, 12; Liu 2013). Preserved small specimens with some speckling on legs.

Distribution: Taiwan (Pingtung) and Philippines (Cebu and Bohol).

Ecology: Similar to Sesarmops impressus (H. Milne Edwards, 1837) in Taiwan and Philippines, but it has sometimes been found to climb large rocks and trees in the Philippines (J-J Li, personal observation).

Remarks: Rathbun (1914: 75–76) described Sesarma (Sesarma) mindanaoensis from a relatively small but adult female specimen (19.6 × 18.2 mm) from a stream in Cotabato in Mindanao, Philippines. No figures were provided, but the author compared it to Pseudosesarma modestum (De Man, 1902) and Sesarmoides longipes (Krauss, 1843). On the basis of the description, Serène and Soh (1970: 401) transferred the species to their new genus, Sesarmops, without discussion. Liu (2013) mentioned there is a population of “Sesarmops mindanaoensis” in Kawasan, Cebu, Philippines, but did not elaborate on the matter. In the ZRC and/or ASIZ contain many specimens from the Philippines and Indonesia that were identified as Sesarmops mindanaoensis by the third author, Christoph Schubart and H-C Liu. This identification was based on comparisons with the holotype female almost 20 years ago, but none of the data have been published.

The present study of the specimens, including new material from Taiwan as well as the type of S. mindanaoensis, confirms their conspecificity. Comparisons of similarly sized female specimens from the Philippines with the type of S. mindanaoensis show that they share many key characters, including the gentle convexity of the dorsal carapace surface (when viewed frontally); the shape of the external orbital angle (acutely triangular and directed obliquely outwards) (Figs. 13B, 14B); relatively more slender ambulatory meri and propodi where the dorsal and ventral margins of P4 and P5 are lined with dense short setae and scattered long setae (Figs. 13F, G, 14E, F); and the outer surface of the chela is smooth or almost so (Figs. 13E, 14D, 15C). The P2–P5 leg proportions may be slightly asymmetrical in some specimens. In the holotype female, the left P3 and P4 propodi are slightly longer (Fig. 13F) than those on the right P3 and P4 (Fig. 13G). There is one female specimen (21.5 × 19.7 mm, ZRC 2014.285) obtained from the Philippines which is similar in size to the holotype female and agrees with it in almost all aspects (Fig. 14), except that its left P2 and P3 propodi are slightly shorter (Fig. 14E) than those on the right instead (Fig. 14F). The ambulatory leg characters, however, do vary slightly. In another similarly sized female from the Philippines (18.8 × 17.8 mm, ZRC 2019.1110), the P4 dactylus and propodus appear proportionately longer and more slender, and the setae lining the margins of the P2–P5 propodus and dactylus are distinctly sparser (Fig. 15E, F) compared to the holotype female. Examining the series of specimens on hand, however, the differences in P3 and P4 meri and propodi, are not significant at the species-level as they are too variable. That being said, none are ever as short and stout as those of S. impressus (Fig. 18E, F). The density of setae on the margins of the ambulatory propodus and dactylus varies in some specimens of S. mindanaoensis, sometimes appearing shorter and less dense; but it is always present (Figs. 13F, G, 14E, F, 15E–H).

Fig. 18.

Sesarmops impressus (H. Milne Edwards, 1837), ovigerous female (26.0 × 24.0 mm) (ZRC 2001.307), Philippines. A, overall dorsal view; B, dorsal view of carapace; C, frontal view of cephalothorax; D, outer view of left chela; E, left ambulatory legs; F, right ambulatory legs.

Comparing the holotype female of S. mindanaoensis with similarly sized female S. impressus, the dorsal surface of the later species is more prominently inflated, the external orbital tooth is clearly directed anteriorly, the ambulatory meri and propodi are distinctly shorter and the outer surface of the chela is distinctly granulated (Fig. 18A–D).

Sesarmops mora n. sp.

(Figs. 11C, D, 19–21)

urn:lsid:zoobank.org:act:93C54D7B-2847-4A82-A9A2-D4A3CEC83A24

Sesarma frontalis – De Man 1892: 334, pl. 19(13). (not Sesarma frontale A. Milne-Edwards, 1869 = Sesarma impressa H. Milne Edwards, 1837).

Material examined: Holotype: 1 male (27.7 × 25.5) (NCHUZOOL 16137), Gangkou R. estuary, Pingtung, Taiwan (21°59'17.3"N 120°50'01.6"E), coll. J.-J. Li, 18 May 2017. Paratypes: 2 females (28.0 × 25.8, 25.2 × 22.6) (NCHUZOOL 16335), same locality as holotype, coll. J.-J. Li, 18 May 2017; 1 female (25.8 × 23.5) (NCHUZOOL 16336), same locality as holotype, coll. J.-J. Li, 11 August 2017; 1 male (13.1 × 13.0) (NCHUZOOL 16337), same locality as holotype, coll. J.-J. Li, 25 September 2018; 1 male (26.0 × 24.2) (ZRC 2019.1111), same locality as holotype, coll. J.-J. Li, 10 June 2019. Others: Philippines: Kawasan, Cebu: 2 males (27.5 × 24.1, 22.4 × 20.7) (ZRC 2019.1653), coll. H.-C. Liu, 2 December 2001; 5 males (33.3 × 30.4, 33.3 × 30.0, 27.7 × 25.6, 29.2 × 26.5, 22.2 × 20.4), 5 females (24.0 × 21.0, 19.6 × 17.1, 19.1 × 17.5, 16.0 × 14.2, 14.2 × 12.6) (ZRC 2019.1655), coll. P. K. L. Ng and C. D. Schubart, 3 December 2001; 2 males (25.0 × 23.1, 21.7 × 19.6) (ZRC 2019.1656), coll. N. K. Ng et al., 2 January 2002; 1 male (31.5 × 28.8), 1 female (27.2 × 24.8) (ASIZ 72950), coll. H.-C. Liu et al., 14 February 2003; 1 male (27.7 × 25.3), 1 female (25.3 × 23.9) (ZRC 2019.1654), coll. P. K. L. Ng et al., 30 July 2003; 1 male (27.3 × 25.1), 1 ovig. female (26.4 × 23.8) (ZRC 2012.0434), coll. P. K. L. Ng and P. Y. C. Ng, December 2010; 1 male (28.6 × 28.1) (NCHUZOOL 14910), coll. J.-J. Li, 6 September 2018. Indonesia: Manado Murex Resort, Sulawesi: 1 female (22.3 × 20.3) (ZRC 2019.1661), coll. P. K. L. Ng et al., 17 July 2003.

Diagnosis of male: Carapace (Fig. 19A, E, F) nearly trapezoid in dorsal view, 1.1 ± 0.04 times broader than long (n = 4); regions well defined, separated by shallow grooves; postfrontal region distinct, separated into 4 lobes by deep grooves; front deflexed downwards, margin distinctly concave in dorsal view. Anterolateral margin with large triangular, exorbital angle and smaller, acutely triangular, epibranchial tooth; lateral margin straight, divergent posteriorly (Fig. 21A). Chelipeds (Figs. 19H, 20C, E) robust, outer surface with numerous rounded granules; dactylus curved, dorsal margin with numerous granules; proximal part of fixed-finger slightly concave, smooth. Ambulatory legs (Figs. 19A, E, F, 20G) slender; P3 and P4 subequal, longer than others, about 2.3 ± 0.1 times carapace width (n = 4). P3 merus 2.6 ± 0.1 times as long as broad (n = 4); upper margin with acute subdistal spine. Propodus of P3 3.2 ± 0.1 times as long as broad (n = 4), with accessory stria on inferior proximal portion of outer surface, dorsal and ventral margins with short stiff setae. Dactylus of P3 0.8 ± 0.1 times length of propodus (n = 4), slightly curved, terminating in acute calcareous tip; dorsal and ventral margins with short stiff setae. Pleon (Fig. 19B) relatively broad, all somites free. Telson semicircular, evenly rounded, as long as preceding somite, base of telson partially inserted in somite 6. G1 (Figs. 20J, K, 21B–D) straight, relatively stout; apical process very short, chitinous part short, ending in truncate tip; setae long, simple, originating at base of apical process. G2 shorter than quarter length of G1.

Fig. 19.

Sesarmops mora n. sp., colour in life. A–C, holotype male (27.7 × 25.5 mm) (NCHUZOOL 16137), Taiwan; D, paratype female (25.8 × 23.5 mm) (NCHUZOOL 16336), Taiwan; E–H, males (specimen not retained), Manado, Sulawesi. A, D, E, F, overall dorsal view; B, ventral view of cephalothorax; C, outer view of chelae; G, dorsal view of carapace; H, outer view of left chela.

Fig. 20.

Sesarmops mora n. sp. A, C, E, G, J, K, holotype male (27.7 × 25.5 mm) (NCHUZOOL 16137), Taiwan; B, D, F, H, I, paratype female (28.0 × 25.8 mm) (NCHUZOOL 16335), Taiwan. A, B, frontal view of carapace; C, D, right chela outer views; E, F, left chela inner views; G, H, P3 merus dorsal views; I, vulvae; J, K, left G1.

Fig. 21.

Sesarmops mora n. sp. A–D, holotype male (27.7 × 25.5 mm) (NCHUZOOL 16137), Taiwan; E, paratype female (25.2 × 22.6 mm) (NCHUZOOL 16335), Taiwan. A, carapace dorsal view; B–D, left G1; E, female. E, left vulvae. Scale bars = 1.0 mm.

Females: Carapace (Fig. 19D) more convex and broader than male, 1.1 ± 0.1 times broader than long (n = 4). Chelipeds (Fig. 19D, F) smaller than male. P3 merus stouter than male, 2.2 ± 0.1 times as long as broad (n = 4). Pleon wide, rounded, telson semicircular, base partially inserted in somite 6. Vulva (Figs. 20I, 21E) on anterior edge of sternite 5, operculum low, oval shaped; posterior and anterior sternal vulvar covers low.

Etymology: The name is derived from the Latin “mora” for delay and procrastination; alluding to the long time it has taken the third author to formally describe this species. The name is used as a noun in apposition.

Colouration in life: Carapace and legs dark brown, without speckling; chelipeds reddish purple to purple (Figs. 11C, D, 19).

Distribution: Taiwan (Pingtung), Philippines (Cebu and Bohol) and Indonesia (Manado, Sulawesi).

Ecology: The habitats of Sesarmops mora n. sp. in Taiwan and Cebu are the river banks far above the high intertidal zone in river estuaries, with muddy substrate and sometimes mixed with some rocks. This species is sympatric with S. mindanaoensis, S. impressus, S. intermedius and Bresedium brevipes in Taiwan (Gangkou R. estuary); or with S. mindanaoensis and B. brevipes in the Philippines (Kawasan, Cebu).

Remarks: Sesarmops mora n. sp. resembles Sesarmops impressus (H. Milne Edwards, 1837) in overall morphology, but differs markedly in having the dorsal surface of the carapace more prominently setose, with numerous clumps of short setae (Fig. 16) (vs. carapace more glabrose in S. impressus); the lateral margins of the carapace are more prominently diverging posteriorly (Fig. 19A, E, F) (vs. more quadrate in S. impressus); the ambulatory merus is proportionately longer (length to width ratio ca. 2.4) (Fig. 19A, E, F) (vs. ambulatory merus relatively shorter in S. impressus, with the length to width ratio ca. 2.2); the length of the adult male telson is subequal to the width (Fig. 19B) (vs. telson length slightly less than the width in S. impressus); the length of male pleonal somite 6 is proportionately shorter (length to width ratio ca. 2.3) (vs. somite 6 relatively longer, with length to width ratio ca. 2.6 in S. impressus); and the elongated chitinous distal part of the G1 is less strongly bent obliquely outwards (Fig. 20J, K) (vs. bent more strongly in S. impressus). Their colours in life differ markedly—the dorsal surface of the carapace of S. impressus is brown with the lateral margins cream or pale yellow; and the outer surface of the chela a uniform purple with white grains. In S. mora, the carapace is a uniform dark to purplish brown without any trace of light-coloured lateral margins (Fig. 19A, E, F), and the outer surface of the chela is dark purple on the dorsal two-thirds and white on the ventral one-third, without white grains (Fig. 19C, H). These differences are valid for the large series of specimens of S. impressus we have examined from Indonesia, Taiwan, Japan, Philippines and Guam.

Sesarmops mora n. sp. is superficially similar to the poorly known P. modestum (from Ternate Island, near Halmahera, Indonesia). Comparing the holotype of P. modestum with that of S. mora, the most obvious characters to distinguish the two species are the relatively narrower carapace, the male telson is distinctly inserted into somite 6 and the G1 is more elongate and slender in S. mora (Figs. 19A, B, D– F, 20J, K, 21B–D) (vs. carapace distinctly wider, the male telson is not inserted into somite 6 and the G1 is proportionately stout and shorter in P. modestum. Pseudosesarma modestum will be redescribed and figured at length in a separate paper revising the genus with allied new species by Schubart and Ng (2020).

DNA Analyses

A 579 bp segment of 16S and 658 bp segment of COI from 12 species (53 specimens) of the Sesarmidae were amplified and aligned (Table 1). A phylogenetic tree of the combined markers was reconstructed using BI and ML analyses (Fig. 22). There are clearly two major clades for most of the species studied, with one clade composed of Bresedium eurypleon n. sp., B. brevipes, Sesarmops impressus 1, S. impressus 2 and S. mora n. sp.; the second clade includes the Sesarmops intermedius complex [including S. sinensis (H. Milne Edwards, 1853)], Pseudosesarma patshuni (Soh, 1978) and Chiromantes dehaani complex [including C. neglectum (De Man, 1887) and C. magnus Komai and Ng, 2013]. Sesarmops mindanaoensis is very different from other species on the tree, coming out far from all the other species. Pseudosesarma can be divided into three groups, (1) P. patshuni; (2) P. bocourti (A. Milne-Edwards, 1869) and P. edwardsii; and (3) P. crassimanum (De Man, 1887). The phylogenetic tree shows that Sesarmops and Pseudosesarma are clearly polyphyletic. The two new species, B. eurypleon and S. mora, described in this study are supported genetically, some species cannot be separated successfully from their closely related species, including Sesarmops intermedius and S. sinensis; as well as Chiromantes dehaani, C. neglectum and C. magnus.

Fig. 22.

Bayesian inference (BI) tree for species of Sesarmidae, based on combined 16S rDNA and cytochrome c oxidase subunit I (COI) genes. Probability values at nodes represent support values for BI and maximum likelihood (ML). For haplotype names, see table 1.

DISCUSSION

In this study, we describe two new species, Bresedium eurypleon n. sp. and Sesarmops mora n. sp, based on a suite of morphological characters, as well as the mitochondrial 16S rDNA and COI markers. The phylogenetic tree (Fig. 22) shows that the two new species are closely related to Bresedium brevipes and Sesarmops impressus. It is clear that Bresedium spp. and three Sesarmops spp. (including S. impressus s. lato and S. mora) are closely related and mixed in one clade, which was noted in Ng et al. (2008). The phylogenetic tree also clearly shows Pseudosesarma and Sesarmops to be polyphyletic. These genera will be revised in the future (PKL Ng et al. unpublished data). Sesarmops mindanaoensis is very different from other species (Fig. 22) and will have to be moved to a new genus at a later date (CD Schubart and PKL Ng, unpublished data). Chiromantes dehaani, Pseudosesarma patshuni and Sesarmops intermedius form another clade (Fig. 22), which has been suggested to be under the same genus in Ng et al. (2008) (see Schubart and Ng 2020).

Sesarmops intermedius and S. sinensis cannot be separated successfully by 16S and COI but can easily be distinguished morphologically (Schubart and Ng 2020). The same situation exists for Chiromantes dehaani, C. neglectum and C. magnus which also forms an unresolved clade (see Schubart and Ng 2020). Closely related species with different morphologies, but not supported by existing molecular data, are a relatively common phenomenon in some freshwater crab groups (see Chu et al. 2015), but they are also occasionally reported in intertidal and supratidal groups. For example, the fiddler crabs of the Gelasimus vocans complex (including G. borealis, G. dampieri, G. vocans, and G. vomeris) (Shih et al. 2010 2016; Chu et al. 2015) and shore crabs of the Helice latimera complex (including H. formosensis, H. latimera and H. tientsinensis) (Shih and Suzuki 2008; Chu et al. 2015; NK Ng et al. 2018). More studies using a series of specimens, as well as more mitochondrial and nuclear markers, will probably be needed to resolve the genetic relationships between these species.

CONCLUSIONS

In our study, two new species, Bresedium eurypleon n. sp. and Sesarmops mora n. sp., are described from Taiwan, the Philippines and Indonesia based on the evidence from morphology (carapace, chelipedal, gonopodal and vulvar characters) and molecular data (mitochondrial 16S and COI). In addition, Bresedium philippinense (Rathbun, 1914) is treated as a junior synonym of B. brevipes (De Man, 1889), and Sesarmops mindanaoensis (Rathbun, 1914) is redescribed.