Abstract
Four synallactid specimens were collected during four deep-water benthic fauna surveys (2013–2018) conducted at three seamounts (‘Jiaolong’, ‘Y3’, and ‘M4’) and the Ganquan Plateau in the South China Sea, tropical Western Pacific Ocean, at depths ranging from 344 to 3610 m. Morphological examination of these specimens revealed four new species belonging to three genera, which are described as Synallactestenuibrachiussp. nov., Bathyplotesliaoisp. nov., Bathyplotesvaricolumnasp. nov., and Amphigymnasganquanisp. nov. Notably, Amphigymnasganquanisp. nov. represents the first report of an Amphigymnas species in the South China Sea. Detailed descriptions are provided for the morphological features, including the type locality, and geographic and bathymetric distributions of these species. These findings contribute to the understanding of seamount biodiversity and provide valuable insights for advancing research on seamount ecology, management, and conservation.
Key words: Amphigymnas , Bathyplotes , new species, ROV, seamounts, Synallactes , taxonomy
Introduction
Holothuroids, commonly known as sea cucumbers, are echinoderms from the class Holothuroidea. They play a critical role in shaping benthic community structure and biogeochemical processes through feeding, fecal production, and locomotory activities (Roberts et al. 2001; Witbaard et al. 2001). Currently, more than 1800 accepted holothuroid species are recognized (WoRMS 2024a), distributed across various marine environments from shallow water to hadal zones (Iken et al. 2001; Jamieson et al. 2011; Lee et al. 2017). The majority of these species are found in the tropical Indo-West Pacific region (Conand 1990). The current classification system for the class Holothuroidea was established by Miller et al. (2017), who conducted extensive molecular phylogenetic analyses of representatives of most families and species-level taxa. Their findings supported the existence of seven orders: Apodida, Dendrochirotida, Elasipodida, Holothuriida, Molpadida, Persiculida, and (Synallactida. Within the order (Synallactida, three families are recognized: the predominantly shallow-water Stichopodidae Haeckel, 1896, and the deep-water Synallactidae Ludwig, 1894, and Deimatidae Théel, 1882. The family Synallactidae is one of the least studied large taxa of deep-sea holothuroids (Solís-Marín 2005; Gebruk et al. 2012; Solís-Marín et al. 2024). It is almost exclusively found in deep-sea habitats (Solís-Marín 2003) and comprises more than 80 accepted species across ten genera (Allopatides Koehler & Vaney, 1905; Amphigymnas Walsh, 1891; Bathyplotes Östergren, 1896; Capheira Ludwig, 1893; Dendrothuria Koehler & Vaney, 1905; Galatheathuria Hansen & Madsen, 1956; Paelopatides Théel, 1886; Pseudothuria Koehler & Vaney, 1905; Scotothuria Hansen, 1978; Synallactes Ludwig, 1894). This variable family is characterized by the absence of tentacle ampullae, a paired gonad, and ossicles composed basically of tables and rods (Solís-Marín 2003, 2005; O’Loughlin and Ahearn 2005). Although new species have been frequently described in recent years, the family Synallactidae remains poorly understood (Thandar 2008; Massin and Hendrickx 2010; O’Loughlin et al. 2013; Samyn and Vandenspiegel 2016; Solís-Marín et al. 2024). This persistent deficiency in taxonomic research presents a significant obstacle to advancing our understanding of the diversity and ecological roles within this family.
Seamounts are unique deep-sea landforms that play an important role in shaping marine biodiversity patterns and processes (Boehlert and Genin 1987; Hannington et al. 1995). They are “diversity hotspots”, often hosting higher species richness than other coastal and oceanic areas (Worm et al. 2003; Samadi et al. 2006; Morato et al. 2008, 2010) and serving as important habitats for benthic invertebrates (Pitcher and Bulman 2007). The tropical Indo-West Pacific region, as the world marine biodiversity center, is one of the priority regions for future research on seamount ecosystems and biodiversity (Xu 2021). This region contains numerous seamounts such as the Yap (Y3), Mariana (M2), and Caroline (M4) seamounts. The South China Sea (SCS), a semi-enclosed marginal sea in the tropical Western Pacific Ocean, includes many seamounts scattered across its abyssal plain (Huang et al. 2023). Although seamounts are acknowledged as highly productive biodiversity hotspots (Clark et al. 2012; Wagner et al. 2020; Yesson et al. 2021), research on these ecosystems remains limited, and reports of Synallactidae from seamounts are particularly rare. To bridge the knowledge gap, the Institute of Oceanology, Chinese Academy of Sciences (IOCAS) conducted several scientific expeditions between 2013 and 2018. During these surveys, four synallactid specimens were collected from three seamounts (named ‘Jiaolong’, ‘Y3’, and ‘M4’) and the Ganquan Plateau in the SCS, at depths ranging from 344 to 3610 m, using the Remotely Operated Vehicle submersible (ROV) ‘Faxian’ (discovery in Chinese) and the manned submersible ‘Jiaolong’ and ‘Shenhaiyongshi’. Detailed examination of ossicles and external morphological features revealed that the four specimens belonged to three genera and represent four new species, which are described and illustrated in this work.
Materials and methods
The Remotely Operated Vehicle submersible (ROV) ‘Faxian’, deployed from the research vessel R/V ‘Kexue’ (science in Chinese), along with the Human Occupied Vehicles (HOVs) ‘Jiaolong’ and ‘Shenhaiyongshi’, were used to collect four synallactid specimens during four surveys conducted in the tropical Western Pacific (2013–2018) (Fig. 1). These specimens were photographed immediately on board prior to preservation. They were then fixed in 95% ethanol for morphological examination and subsequently stored in the Marine Biological Museum of Chinese Academy of Sciences (MBMCAS) at Qingdao, China. Due to the limited availability of molecular data for Synallactidae, identification of the four specimens relied solely on morphological characteristics.
Figure 1.
Sampling sites of the studied holothuroid species from tropical Western Pacific, showing the location of three seamounts.
Morphological observations were performed using a stereomicroscope (ZEISS Stemi 2000-C, Wetzlar, Germany). To prepare ossicles, soft tissues from the body wall, tentacles, papillae, and tube feet were digested in a solution of 15% sodium hypochlorite for 4–5 h. The digested samples were then rinsed with distilled water, air-dried, mounted on aluminum stubs, and coated with gold. The ossicle features of the four specimens were examined and photographed under a Nikon Eclipse Ni-U microscope (Tokyo, Japan) and a Hitachi S-3400N (Tokyo, Japan) scanning electron microscope (SEM).
Abbreviations used in the text: ROV, Remotely Operated Vehicle submersible; HOV, Human Occupied Vehicles; IOCAS, the Institute of Oceanology, Chinese Academy of Sciences; MBM, Marine Biological Museum of Chinese Academy of Sciences, Qingdao, China; RN, registration number; CN, collection number; SCS, South China Sea; SEM, scanning electron microscope.
Systematics
Order Synallactida Miller, Kerr, Paulay, Reich, Wilson, Carvajal & Rouse, 2017
Family Synallactidae Ludwig, 1894
Genus. Synallactes
Ludwig, 1894
DF86076A-8E6F-5CE6-9DA0-C4D84069FA00
Diagnosis.
Body cylindrical or subcylindrical. Tentacles 18–20. Ventral surface flattened, without any marginal border. Ventral tube feet and dorsal papillae in longitudinal series, confined to ambulacra. Three zones of tube feet on ventral surface. Body wall with tri- or quadri-radiate tables, the distal ends of the arms with a larger or smaller number of perforations, often lateral processes forming a complex lattice-like network with similar processes of other arms. Spire consisting of a single pillar, terminally divided or perforated, or both [adapted from Solís-Marín 2005: 570–571].
Type species.
Synallactesalexandri Ludwig, 1894.
Type locality.
North Pacific Ocean, Azuero Peninsula, Gulf of Panama, depth 588 m (Solís-Marín 2003).
Synallactes tenuibrachius sp. nov.
4AD8E6FC-48BE-5724-A7A2-EC01B548452C
https://zoobank.org/B4D25768-197C-41A8-8363-7D3EB2AB17FF
Figure 2.
Synallactestenuibrachius sp. nov. holotype: MBM286921 A, B living specimen C, D preserved specimen C dorsal view D ventral view. Scale bar: 2 cm.
Figure 3.
SEM images of Synallactestenuibrachius sp. nov. holotype: MBM286921. Ossicles from A1–A10 dorsal body wall B1–B2 papillae C1–C5 ventral body wall D1–D10 ventral tube feet. Scale bars: 100 μm.
Material examined.
Holotype • West Pacific, the Jiaolong Seamount in the SCS, depth 3610 m, 5 Jul. 2013, preserved in 95% ethanol, CN: III, RN: MBM286921.
Diagnosis.
Body subcylindrical, convex dorsally, flattened ventrally. Mouth and anus terminal. Dorsal papillae conical, scattered on the bivium, with alternating large and small papillae. Ventrolateral papillae placed in a single row on each body side. Midventral radius with one or two small tube feet at the anterior and posterior ends. Ventrolateral tube feet arranged in double alternate rows. Dorsal body wall perforated plates and tables, tables with four or five slender arms. Papillae with tables, spires of tables higher than those of tables in the dorsal body wall. Ventral body wall tables with four or five arms. Tables with 4–6 arms in ventral tube feet, the distal ends of the arms enlarged, branched, rarely connected, and possessing a number of perforations.
Description.
Body subcylindrical, slightly convex dorsally, flattened ventrally. Skin soft and gelatinous. Color red in life (Fig. 2A, B). After 95% ethanol fixation, color white, body length 9 cm and width 4 cm (Fig. 2C, D). Mouth and anus terminal. Tentacles, calcareous ring, and polian vesicles lost. Dorsal surface with numerous large and small papillae, scattered all over the bivium (Fig. 2A–C). Large papillae arranged in longitudinal rows along dorsal radii, ~ 10 in each row; small papillae mainly distributed in both dorsal interradii, ~ 20 on each body side (Fig. 2C). Ventrolateral papillae large, forming a simple row around the margin of the brim (Fig. 2A, B). Ventrolateral tube feet conical, arranged in a double alternate row, ~ 22 on each body side (Fig. 2D). Midventral tube feet radius with one or two small tube feet at the anterior and posterior ends of the body (Fig. 2D). Ossicles. Dorsal body wall tables with four or five arms (Fig. 3A1–A9), arms slightly broader at the tip with one or two perforations, 50–70 μm in length, spires with simple tips, often bearing several spines on the side, 82–100 μm in height; simple concave perforated plates (Fig. 3A10), 75 μm in diameter. Papillae with four-armed tables (Fig. 3B1, B2), the spires significantly higher than those in the dorsal body wall, 110–155 μm in height. Ventral body wall with tables similar to those in the dorsal body wall (Fig. 3C1–C5), except that the end of arms bifurcated or bearing more perforations (up to 5) in some tables. Tables with 4–6 arms in ventral tube feet (Fig. 3D1–D10), irregular in shape, the distal ends of the arms enlarged, branched, and possessing several perforations, sometimes the enlarged ends of the arms connected with one another (Fig. 3D1); rarely a four-armed table with two parallel pillars (Fig. 3D8), ~ 68 μm in height, without transverse beam.
Type locality.
The Jiaolong Seamount in the South China Sea, tropical Western Pacific, depth 3610 m.
Etymology.
The name of the new species is a combination of the Latin words tenuis meaning ‘slender’ and brachium meaning ‘arm’. It refers to the very slender arms of tables in the body wall.
Distribution.
Only known from its type locality.
Remarks.
The new species, Synallactestenuibrachius sp. nov., is characterized by the tube feet arranged in a double alternate row along each ventrolateral radius and all tables possessing very slender arms. Among the five species of Synallactes with single-pillared tables featuring pointed tops (i.e., S.aenigma, S.horridus, S.robertsoni, S.profundus, and S.laguardai; Solís-Marín 2003; Solís-Marín 2005), the new species most resembles S.aenigma Ludwig, 1894, S.horridus Koehler & Vaney, 1905, and S.profundus (Koehler & Vaney, 1905) based on the ossicle features of the body wall. Specifically, all have single-pillared tables with pointed tops and four- or five-armed discs, with the distal ends of the arms exhibiting only a few perforations. However, there are some differences between them. Compared with S.aenigma: 1) In the new species, the midventral ambulacrum bears only one or two small tube feet at the anterior and posterior ends of the body. In contrast, Ludwig (1894) noted that S.aenigma possesses a few tube feet organized into two long rows on the midventral radius. 2) The anus in S.tenuibrachius sp. nov. is terminal, whereas in S.aenigma, it is dorsal. 3) The spires in S.tenuibrachius sp. nov., are generally unbranched at the end, with some arms having enlarged ends that may connect to each other, while in S.aenigma, the spires of tables are divided into 2–10 elongated tips at the end, and the arms of tables never seem to be connected. 4) Synallactestenuibrachius sp. nov. differs from S.aenigma by the types of ossicles in the tube feet. The tube feet of S.tenuibrachius sp. nov. have only tables, whereas those of S.aenigma have spiny, curved support rods, and well-developed mesh-like discs in addition to tables.
Compared with S.horridus: 1) S.tenuibrachius sp. nov. exhibits numerous large and small papillae scattered on the dorsal surface and only one or two small tube feet placed on the midventral ambulacrum at the anterior and posterior ends of the body. By contrast, S.horridus has large conical papillae on all radii except midventral radius, and some tube feet are confined to the anterior region of midventral radius. 2) The body wall of S.tenuibrachius sp. nov. contains tables with cross-shaped discs and small perforated plates, but no rods, while the body wall of S.horridus has many cruciform bodies and rods, with perforated plates absent. 3) All the arms and spires of tables in the body wall of S.tenuibrachius sp. nov. are more slender and fragile, compared to the solid and high spires of the cruciform bodies in the body wall of S.horridus.
Compared with S.profundus: The new species differs from S.profundus by the arrangement and number of the ventral tube feet. The tube feet in S.tenuibrachius sp. nov. are arranged in a double alternate row on each ventrolateral radius, while the midventral radius is completely naked. In S.profundus, the tube feet are arranged in a single row on each ventrolateral radius, with the midventral radius hosting a few tube feet near the anterior and posterior ends.
Genus. Bathyplotes
Östergren, 1896
89A098C4-0556-514F-972D-0505242DCBB9
Diagnosis.
Tentacles 15–20. Mouth ventral, anus dorsal, subdorsal or nearly terminal. Skin rather thick. Body with sole-like ventral side, usually with marginal appendages. Midventral ambulacrum with a few tube feet or naked. Ventrolateral tube feet arranged in a single row or multiple rows. Dorsal papillae more or less distinctly arranged in rows. Tables with cross-shaped disc and a spire formed by 1–5 pillars, usually with several transverse beams (rarely without transverse beams); C- shaped bodies may be present [adapted from Solís-Marín 2003: 124].
Type species.
Bathyplotesnatans (Sars, 1868) by original designation.
Type locality.
Lofoten, northern Norway, depth 366–549 m.
Bathyplotes varicolumna sp. nov.
FAE422C6-6426-522C-B71E-AE9315D6ACD9
https://zoobank.org/7E4D63FA-EB18-4906-96BB-57E8B25315B8
Figure 4.
Bathyplotesvaricolumna sp. nov. holotype: MBM286925 A in situ image B tentacles C dorsal view D ventral view. Scale bar: 3 cm.
Figure 5.
SEM images of Bathyplotesvaricolumna sp. nov. holotype: MBM286925. Ossicles from A dorsal papillae B ventral body wall C ventral tube feet D tentacles E ‘fungiform’ whitish warts. Scale bars: 100 μm.
Material examined.
Holotype • West Pacific, the M4 Seamount located in the Caroline Ridge, Dive FX-Dive137 (10°35.04'N, 140°07.27'E), depth 1195 m, 21 Aug. 2017, preserved in 95% ethanol, CN: C144, RN: MBM286925.
Diagnosis.
Body elongated, ventrally flattened. Mouth ventral, anus terminal. Peltate tentacles 16. Dorsal surface with scattered large papillae and laterally with a simple row of small papillae. The dorsal side irregularly arranged with several low ‘fungiform’ whitish warts. Ventral surface with scattered minute tube feet. Dorsal body wall lacking ossicles. Papillae cross-shaped tables and rods, tables with 4–7 arms, 3–5 pillars, and without transverse beams. Cross-shaped tables with single pillars in low whitish warts. Cross-shaped tables with single pillars, support rods, and irregular shaped ossicles in the ventral body wall. Cross-like discs of tables, perforated plates, and support rods in ventral tube feet. Rods, smaller tables, and irregular deposits in tentacles.
Description.
Body elongated, ventrally flattened, body wall thin and pliable. Color pale pink in situ, and orange in life (Fig. 4A, B). Body 24 cm long and 6.5 cm wide in living specimen (Fig. 4C, D). Mouth ventral, anus terminal. Peltate tentacles 16. Circum-oral papillae present (Fig. 4B). Bivium with some scattered large papillae and laterally with a simple row of small papillae (Fig. 4A, C). A number of low whitish warts arranged along the two dorsal interradii (Fig. 4C). Trivium with some scattered minute tube feet (Fig. 4B, D). Ventral surface with three series (a middle series and one lateral series on each side) of tube feet (Fig. 4D), the middle series forming multiple rows, occupying a third of the ventral surface, other two series forming two or three rows on each side. Brim narrow and retracted, formed by ventrolateral papillae (Fig. 4A, B). Ossicles. Dorsal body wall lacking ossicles. Dorsal papillae with tables and rods (Fig. 5A), cross-shaped discs of tables 190–260 μm across, with 4–7 arms, each arm ~ 45–155 μm long, the ends of the arms enlarged and pierced with holes, the spires composed of 3–5 pillars, without transverse beams, the top of pillars fused, making the tip of spires spinous; rods curved, 280–315 μm long. Ventral body wall with tables, rods and irregularly shaped ossicles (Fig. 5B), cross-shaped discs of tables with four arms, and only one central pillar (often truncated); rods up to 95 μm. Cross-like discs of tables in ventral tube feet 100–222 μm across, with 1–4 pillars, without transverse beams, the top of pillars fused; terminal plates and rods also in tube feet (Fig. 5C). Rods, smaller tables, and irregular deposits in tentacles (Fig. 5D). Tables with four arms in low whitish warts similar to those in the ventral body wall, and possessing only one central pillar, the top of pillars often irregularly branched or truncated (Fig. 5E).
Type locality.
The M4 Seamount located in the Caroline Ridge of the tropical Western Pacific, depth 1195 m.
Etymology.
The Latin word varicolumna means ‘various pillars’ and is used to describe tables characterized by different types of pillars.
Distribution.
Only known in its type locality.
Remarks.
The body of the new species, with a sole-like ventral side, and its tables featuring cross-shaped discs with typically three or four pillars, confirm its placement within the genus Bathyplotes. In most Bathyplotes species, tables generally possess four pillars, rarely three or five. However, in the new species, tables exhibit a broader variation, with 1–5 pillars, and 4–7 arms, an uncommon variation within this genus. Among the known species of Bathyplotes, the morphology of Bathyplotesvaricolumna sp. nov. most closely resembles that of B.moseleyi. Both species share tables with numerous arms and dorsal interradii bearing numerous low whitish warts.
Nonetheless, the new species can be distinguished from B.moseleyi by the following differences: 1) Both B.moseleyi and the new species possess three series of tube feet on the ventral surface: a middle series and one lateral series on each side. However, the middle tube feet in B.moseleyi are arranged in a thin double row, whereas the middle tube feet in B.varicolumna sp. nov. are scattered irregularly and broadly along the midventral radius. 2) In B.moseleyi, tables have discs with 4–8 arms, and their spires are formed by four pillars and one, rarely two transverse beams, or are often entirely devoid of transverse beams. In contrast, the tables in B.varicolumna sp. nov. have discs with 4–7 arms, and their spires consist of 1–5 pillars without transverse beams. 3) The tube feet of B.moseleyi contain support rods, whereas those of B.varicolumna sp. nov. possess tables and terminal plates in addition to rods. 4) In B.moseleyi, whitish warts contain only a few rods at their ends. In B.varicolumna sp. nov., however, the predominant ossicles are four-armed tables with cross-shaped discs, supported by a single central pillar that is often irregularly branched or truncated at the top.
Bathyplotes liaoi sp. nov.
7C8F86E9-4A92-51B3-8050-F3740D59E862
https://zoobank.org/F8A68557-64F1-41B9-B1C4-8F536D013EDD
Figure 6.
Bathyplotesliaoi sp. nov. holotype: MBM286918 A in situ image B dorsal view C ventral view. Scale bar: 3 cm.
Figure 7.
SEM images of Bathyplotesliaoi sp. nov. holotype: MBM286918. Ossicles from A1–A7 dorsal body wall B1–B5 dorsal papillae C1, C2 ventral body wall D tentacles E1–E8 tube feet. Scale bars: 200 μm.
Figure 8.
Optical microscope images of Bathyplotesliaoi sp. nov. holotype: MBM286918. Ossicles from ventral body wall A, B tables with very high spires and four-armed discs C small tables with annular discs D annular discs E perforated plates. Scale bars: 50 μm.
Material examined.
Holotype • West Pacific, the Y3 Seamount near the Yap Trench, Dive FX-Dive 21 (8°51'N, 137°47'E), depth 344 m, 24 Dec. 2014, preserved in 95% ethanol, CN: Y30165, RN: MBM286918.
Diagnosis.
Body elongated, dorsally convex, ventrally flattened. Mouth ventral, anus dorsal. Tentacles 18. Dorsal papillae arranged in six longitudinal rows. Brim formed by small ventrolateral papillae. Tube feet irregularly scattered on the ventral surface. Dorsal body wall containing tables with cross-shaped discs, four (rarely five) pillars of tables bearing numerous large spines, and four to six transverse beams; small tables with annular discs; perforated plates. Dorsal papillae with perforated plates, tables with cross-shaped discs, and support rods. Ventral body wall ossicles similar to those in the dorsal body wall, except for some tables with much higher spires. Tube feet with perforated plates, irregularly shaped ossicles, and small tables with annular discs. Tentacles with spiny rods.
Description.
Body elongated, slightly pointed at each extremity, dorsal slightly arched, ventral flattened (Fig. 6A–C). Color in life faint yellow, sub-transparent, dorsal papillae, tube feet, and tentacles darker (Fig. 6B, C). Body 15 cm long and 5 cm wide before fixation (Fig. 6B, C). Mouth ventral, anus dorsal and surrounded by numerous small papillae (Fig. 6B, C). Peltate tentacles 18. Dorsal surface densely covered with approximately equal conical papillae, arranged in six longitudinal rows, with ~ 14–18 papillae in each row (Fig. 6A, B). The jagged edges on both sides of the body formed by a single row of numerous smaller papillae. Tube feet irregularly arranged longitudinally throughout the ventral sole, ~ 86 in each row. Ossicles. Tables of two types in the dorsal body wall (Fig. 7A1–A7): 1) Cross-shaped discs (Fig. 7A1–A4) with four arms, each arm bearing small spines, 100–200 μm in length, with a number of perforations at the ends, four (rarely five) pillars bearing numerous large spines, four to six transverse beams, the spires measuring 108–200 μm in height, tips formed by fused pillars. 2) Annular discs (Fig. 7A5–A7) with four large holes formed by simple diagonal bars, discs ~ 58 μm in diameter, the spires 30–42 μm high, with one or two transverse beams. Dorsal papillae with most tables (Fig. 7B1–B4) similar to those of the dorsal body wall (first type), rarely smaller tables with four transverse beams (Fig. 7B4); perforated plates, measuring 400 μm in diameter (Fig. 7B5); spinous rods up to 366 μm in length (Fig. 7B4). Ventral body wall tables with four-armed discs, small tables with annular discs, and perforated plates (Fig. 7C1, C2 and Fig. 8), most ossicles of similar features to those in the dorsal body wall, except that a few tables with really high spire, measuring 245 μm in height (Fig. 8A, B). In tentacles (Fig. 7D) rods 70–500 μm long. Tube feet with four types of ossicles: 1) perforated plates (Fig. 7E1); 2) smaller tables with annular discs (Fig. 7E2–E7), ~ 88 μm in diameter, the spires of tables higher than those in the dorsal body wall (second type), measuring 48–64 μm high, four spiny pillars with three transverse beams; 3) rods up to 404 μm in length (Fig. 7E8).
Type locality.
The Y3 Seamount near the Yap Trench, tropical Western Pacific, 344 m depth.
Etymology.
The species is named after one of the pioneers in the study of holothuroid fauna in China, Professor Yulin Liao.
Distribution.
Only known from its type locality.
Remarks.
The predominance of four-pillared tables undoubtedly indicates that this species belongs to the Bathyplotes. Bathyplotesliaoi sp. nov. is mostly similar, in terms of ossicle types, to Bathyplotespatagiatus Fisher, 1907, which has been regarded as a synonym of Bathyplotesnatans. Both species share the presence of ossicles that include four-armed crosses, small tables with annular discs, and spinous rods. However, the new species can be distinguished from B.patagiatus by the presence of tube feet on the midventral radius and differences in the shape of the spires of tables. In Bathyplotesliaoi sp. nov., the tables typically have four, rarely five pillars, with their dilated ends of spires usually formed by these fused pillars, rather than expanding into a crown. In contrast, the tables in B.patagiatus are robust, with each table possessing four pillars and a broad thorny crown formed by the highly dilated spire ends, resembling a quadrilateral tower. Moreover, the pillar ends in B.patagiatus are often unfused. The new species also differs from B.patagiatus by the presence of tables with annular discs and five-pillared crosses in the dorsal body wall, as well as perforated plates in the ventral body wall and papillae. In B.liaoi sp. nov., the arms of the crosses bear small spines, whereas those in B.patagiatus are smooth. The spines on the spires of tables in B.liaoi sp. nov. are distributed along the entire length of the pillars, while in B.patagiatus, the spines are confined to the upper half, even in tables with exceptionally long spires. In addition, B.liaoi sp. nov. lacks C-shaped ossicles present in B.patagiatus.
Both Bathyplotesliaoi sp. nov. and B.phlegmaticus have two types of tables in the body wall: 1) large tables of characteristic form, with cross-like discs and 2) smaller tables with annular discs. The arms and pillars of both types of tables possess spines. However, the new species exhibits several key differences from B.phlegmaticus: 1) The number and arrangement of papillae are different. In B.liaoi sp. nov.: the dorsal surface was densely covered with conical papillae of approximately equal size, arranged in six longitudinal rows, with ~ 14–18 papillae each row. The jagged edges along both sides of the body were formed by a single row of numerous smaller papillae. In B.phlegmaticus, a delicate rim was formed by free papillae, with ~ 35 at the anterior part of the body and ~ 12 along the anterior and posterior lateral edges. Papillae on the ventral side are few, irregularly distributed, and not confined to the radii. 2) Tube feet in B.phlegmaticus have rods and a well-developed endplate. However, tube feet in B.liaoi sp. nov. include tables with annular discs, irregular large ossicles, rods, and a plate. 3) Tables have different numbers of transverse beams. In B.phlegmaticus, the spires of large tables possess 6–8 transverse beams, while smaller tables have 1–3 transverse beams. In B.liaoi sp. nov., the large tables have fewer transverse beams (4–6), and the smaller tables have only one or two transverse beams.
Genus. Amphigymnas
Walsh, 1891
8A278E91-808F-5D6A-A614-94861A9BA6E2
Diagnosis.
Body wall calcareous, brittle, similar to that of the elasipodid family Deimatidae. Mouth ventral, peltate tentacles 20. Dorsal and lateral body with long conical calcareous papillae, including a ventrolateral series. Body flat ventrally, tube feet in ambulacral series or scattered. Anus subdorsal posterior. Ossicles in body wall large table discs with many perforations, discs variably with or lacking spires often comprising three or four pillars, sometimes with more fused pillars, without distal spines or teeth, spires sometimes reduced to short unconnected pillars [adapted from O’Loughlin et al. 2013: 38].
Type species.
Amphigymnasmultipes Walsh, 1891 accepted as Amphigymnaswoodmasoni (Walsh, 1891).
Type locality.
Indian Ocean, Andaman Sea, off Dyer Point and North Cinque Island, depth 343–402 m.
Amphigymnas ganquani sp. nov.
63276A58-F401-5F39-988B-8225248F17B5
https://zoobank.org/B0A06953-CB2A-41AD-97D2-295D92330F52
Figure 9.
Amphigymnasganquani sp. nov. holotype: MBM286926 A, B in situ images C holotype after fixation D tentacles. Scale bars: 1 cm.
Figure 10.
SEM images of Amphigymnasganquani sp. nov. holotype: MBM286926. Ossicles from A–J dorsal body wall K–X dorsal and lateral papillae. Scale bar: 100 μm.
Figure 11.
SEM images of Amphigymnasganquani sp. nov. holotype: MBM286926. Ossicles from A ventral body wall B tentacles C–G tube feet. Scale bars: 100 μm (A, E–G); 300 μm (B–D).
Material examined.
Holotype • West Pacific, the Ganquan Plateau in the SCS, depth 1350 m, 12 May 2018, preserved in 95% ethanol, CN: GQHT-SY-066-12, RN: MBM286926.
Diagnosis.
Body elongated, cylindrical, gradually tapering at both ends. Color yellowish white. Skin fragile, glass-like. Mouth ventral, oral disc with front-suspended dorsal papillae, anus terminal. Peltate tentacles 20. Dorsal papillae arranged in two rows along each dorsal ambulacrum. Ventrolateral papillae arranged in a single row. Ventrolateral tube feet arranged in a single row on each side. Midventral ambulacrum placed in alternate two rows. Dorsal body wall tables with short or high 4-pillared spires and 0–2 transverse beams. Papillae tables and widened midrods, tables with higher spires, four or more usually fused pillars, and three or four transverse beams. Ventral body wall with smaller tables, spires truncate, without transverse beams. Tube feet tables with truncate and high pillars. Tentacles support rods.
Description.
Body long and cylindrical, slightly slender at both ends (Fig. 9A, B), ventral flattened. Body 28 cm long, 2.5 cm wide mid-body before fixation (Fig. 9C). Color yellowish white, body wall thin, calcareous, and fragile. Mouth ventral, anteriorly overhung by a few dorsal papillae (Fig. 9C, D), anus terminal. Peltate tentacles 20, measuring 0.25–0.3 cm in diameter after fixation (Fig. 9D). Two paired conical papillae placed in a single series on each dorsal radius (four rows across dorsally), each up to 1 cm long after fixation. Ventrolateral papillae arranged in a single row, ~ 22 on each body side, up to 1.5 cm long after fixation. Irregular tube feet relatively large and placed in single rows on ventrolateral radii, ~ 60 in each row. Midventral tube feet small, placed in alternate two rows, ~ 80 in each row. Longitudinal muscles undivided, tentacle ampullae absent, and gonads arranged in clusters. Ossicles. Dorsal body wall tables (Fig. 10A–J), discs perforated plates, edges usually incomplete, 220–370 μm across, with numerous perforations of similar size, spires with four pillars (mainly) or more pillars (Fig. 10G, H, J), short or relatively high, lacking or possessing one (rarely) or two transverse beams. Short pillars lacking or with one beam, ~ 50–80 μm in length (Fig. 10A–C, F–J), relatively high pillars with two beams, 100–120 μm in length (Fig. 10D, E). Spires of tables in dorsal and lateral papillae possessing much higher and firmer spires (Fig. 10K–W) than those in dorsal body wall, discs up to 400 μm across, with four large central perforations and many small outer perforations, four or more pillars, up to 150 μm in length, usually fused, making the number of transverse beams uncertain, some spires of tables possibly possessing 3–4 transverse beams; widened midrods in papillae up to 600 μm long, with marginal projections (Fig. 10X). Ventral body wall with smaller tables (Fig. 11A), discs 144–267 μm across, edges more complete and smooth, spires truncate, without transverse beams. Tentacles predominantly rods, curved, bearing irregular marginal projections, up to 803 μm long (Fig. 11B). Tube feet support rods straight to curved, widened midrods bearing irregular marginal projections, some placing through the entire length (Fig. 11C–E); tables with truncate pillars (Fig. 11F), without transverse beams; tables with high pillars, possessing four beams (Fig. 11G).
Type locality.
The Ganquan Plateau in the South China Sea, tropical Western Pacific, depth 1350 m.
Etymology.
The specific name refers to the Ganquan Plateau, where the holotype was sampled.
Distribution.
Currently known from the type locality.
Remarks.
The new species belongs to Amphigymnas Walsh, 1891, characterized by the glass-like body wall formed by numerous large tables, large conical papillae on the dorsal and ventrolateral radii, and a midventral row of small tube feet filled with many support rods.
The new species differs from the A.bahamensis Deichmann, 1930 by the arrangement of ventral tube feet and the number of pillars of dorsal tables. Dorsal tables in the new species have at least four pillars, whereas those of A.bahamensis have rare 3-pillared truncate spires. Additionally, the ventral tube feet in the new species are arranged along both the ventrolateral and midventral radii, while those in A.bahamensis are restricted to the midventral radius. The external morphological differences between the new species and Amphigymnaswoodmasoni are slight. However, the new species can be distinguished primarily by ossicle features: Tables in A.woodmasoni have four large central perforations surrounded by many smaller peripheral holes, and the spires of tables are usually rather primitive and reduced to four spines (without forming pillars) on the body walls and papillae. In contrast, the spires of tables on body walls and papillae in the new species are relatively high and often exhibit four or more pillars, rather than being reduced to spines. Notably, in the papillae they can reach heights of up to 150 μm. In comparison to Amphigymnasstaplesi O’Loughlin in O’Loughlin et al. 2013, the new species exhibits several distinguishing characteristics: The oral disc of A.staplesi is surrounded by a continuous series of papillae, whereas the new species has only front-suspended dorsal papillae. The new species is quite different from A.staplesi by the ossicle features: 1) In A.staplesi, the tables of dorsal body wall have discs with four large central perforations and many smaller outer perforations, and the spires have four pillars and two transverse beams. In the new species, the dorsal tables have discs with perforations of approximately equal diameters, and the spires have four or more pillars and 0–2 transverse beams; 2) The pillars of the new species are relatively higher, sturdier, and often irregularly fused, distinguishing them from those in A.staplesi; 3) Additionally, the new species possesses support rods, which are absent in A.staplesi; 4) The new species lacks endplates in its ventrolateral tube feet, whereas A.staplesi possesses endplates.
The genus Amphigymnas was newly recorded in the SCS, and the discovery of the new species expands the geographical distribution of this genus.
Discussion
Until recently, a total of ten genera and 85 accepted species in the family Synallactidae (WoRMS 2024b). Using distribution data from published literature and findings from this study, we examined the geographical distribution and species diversity of synallactids across the world’s oceans, with a particular focus on the tropical Western Pacific. Table 1 presents a summary of the distribution of synallactid species in the Pacific Ocean, with a focus on the tropical Western Pacific.
Table 1.
Overview of the distribution of synallactid species in the Pacific Ocean and tropical Western Pacific.
| Genus | Number of accepted species | Number of species in the Pacific Ocean | Species in the tropical Western Pacific | |
|---|---|---|---|---|
| Number | Species | |||
| Allopatides | 2 | 1 | 1 | A.corrugatus |
| Capheira | 2 | 0 | 0 | – |
| Dendrothuria | 2 | 1 | 1 | D.megalopharynx |
| Galatheathuria | 1 | 1 | 1 | G.aspera |
| Paelopatides | 21 | 7 | 3 | P.appendiculata, P.illicitus, and P.ovalis |
| Pseudothuria | 1 | 0 | 0 | – |
| Scotothuria | 1 | 0 | 0 | – |
| Synallactes | 27 | 15 | 9 | S.chuni, S.discoidalis, S.gilberti, S.heteroculus, S.monoculus, S.multivesiculatus, S.nozawai, S.sagamiensis, and S.triradiate |
| Bathyplotes | 25 | 13 | 9 | B.angustus, B.cinctus, B.crebrapapilla, B.dofleinii, B.imperfectus, B.moseleyi, B.natans, B.punctatus, and B.sulcatus |
| Amphigymnas | 3 | 1 | 1 | A.woodmasoni |
| Total | 85 | 39 | 25 | – |
In summary, more than half of the species within each genus described occur in the Pacific Ocean, with 29 synallactid species (including the four new species described here) identified in the deep water of the tropical Western Pacific. This represents over one-third of all species in the family Synallactidae, highlighting the higher synallactid species richness of this region. However, only three species (i.e., Synallactestenuibrachius sp. nov., Amphigymnasganquani sp. nov., and Galatheathuriaaspera) have been reported in South China Sea. This underscores the need for further deep-sea biodiversity surveys in the SCS to better understand the diversity, distribution patterns, and ecological characteristics of holothuroid fauna in this underexplored region. Such studies will contribute to global marine biodiversity knowledge, support regional conservation strategies, and inform ecosystem-based management approaches for the tropical Western Pacific.
Supplementary Material
Acknowledgments
We are grateful to the crews of R/V Kexue for their work in the collection of the specimens during the survey. We appreciate the scientists of the Department of Marine Organism Taxonomy & Phylogeny, Institute of Oceanology, Chinese Academy of Sciences (IOCAS) for their help in taking photographs of fresh specimens on board.
Citation
Xiao Y, Xiao N (2025) Description of four new synallactid species (Holothuroidea, Synallactida, Synallactidae) from the tropical Western Pacific Ocean. ZooKeys 1231: 347–370. https://doi.org/10.3897/zookeys.1231.142729
Funding Statement
This work was supported by the National Natural Science Foundation of China (No. 42376135 and No. 42176114), the NSFC Innovative Group Grant (No. 42221005) and the Senior User Project of RV KEXUE (KEXUE2020GZ01), the National Key Research and Development Program of China (2023YFC2809300).
Additional information
Conflict of interest
The authors have declared that no competing interests exist.
Ethical statement
No ethical statement was reported.
Funding
This work was supported by the National Natural Science Foundation of China (No. 42376135 and No. 42176114), the National Science Foundation for Distinguished Young Scholars (42025603), the NSFC Innovative Group Grant (No. 42221005) and the Senior User Project of RV KEXUE (KEXUE2020GZ01), the National Key Research and Development Program of China (2023YFC2809300).
Author contributions
Yunlu Xiao conceived and designed this project, performed morphological examination and description, conducted molecular analyses, and wrote or reviewed drafts of the paper. Ning Xiao conceived and designed this project, reviewed and edited drafts of the paper and approved the final draft.
Author ORCIDs
Yunlu Xiao https://orcid.org/0009-0005-9787-033X
Data availability
All of the data that support the findings of this study are available in the main text.
References
- Boehlert GW, Genin A. (1987) A review of the effects of seamounts on biological processes. In: Keating BH, Fryer P, Batzia R, Boehlert GW (Eds) Seamounts, Islands, and Atolls. American Geophysical Union, Washington DC, 319–3 10.1029/GM043p03190319 [DOI]
- Clark MR, Schlacher TA, Rowden AA, Stocks KI, Consalvey M. (2012) Science priorities for Seamounts: Research links to conservation and management. PLoS ONE 10.1371/journal.pone.00292329232 [DOI] [PMC free article] [PubMed]
- Conand C. (1990) The Fishery Resources of Pacific Island Countries: Holothurians. Food & Agriculture Organization, Rome, 143 pp. [Google Scholar]
- Fisher WK. (1907) The Holothurians of the Hawaiian Islands. United States National Museum, Smithsonian Institute Press, Washington D.C 32: 637–7 10.5479/si.00963801.32-1555.637.637 [DOI]
- Gebruk AV, Solís-Marín FA, Billett DSM, Rogacheva AV, Tyler PA. (2012) Review of the genus Zygothuria Perrier, 1898 and the Atlantic group of species of the genus Mesothuria Ludwig, 1894 (Synallactidae: Holothuroidea) with description of the new species Mesothuriamilleri sp. nov. Journal of Natural History 46: 265–3 10.1080/00222933.2011.6384238423 [DOI]
- Haeckel E. (1896) Systematische Phylogenie der Echinodermen. pp. 348–504. In: Systematische Phylogenie der Wirbellossen Thiere (Invertebrata): Zweiter Teil des Entwurfs einer systematischen Stammengeschichte. Reimer, Berlin, 720 10.1515/97831114439353935 [DOI]
- Hannington MD, Jonasson IR, Herzig PM, Petersen S. (1995) Physical and chemical processes of seafloor mineralization at mid-ocean ridges. In: Humphris SE, Zierenberg RA, Mullineaux LS, Thomson RE (eds) Seafloor hydrothermal systems: physical, chemical, biological, and geological Interactions. Geophysical Monograph 91: 115–1 10.1029/GM091p01150115 [DOI]
- Hansen B. (1978) Scotothuriaherringi, a new genus and species of bathypelagic holothurians (Holothurioidea, Aspidochirota, Synallactidae). Steenstrupia 5(4): 33–39. [Google Scholar]
- Hansen B, Madsen FJ. (1956) On two bathypelagic holothurians from the South China Sea, Glatheathuria n. g. aspera (Théel) and Enypniastesglobosa n. sp. Galathea Reports 2: 55–60. [Google Scholar]
- Huang H, Xu S, Li S, Wang X, Guo K, Yan R, Xie W, Yin K. (2023) Diversity and Distribution of Harmful Algal Bloom Species from. Microbiology Spectrum 11: 1– 10.1128/spectrum.04169-229-22 [DOI] [PMC free article] [PubMed]
- Iken K, Brey T, Wand U, Voigt J, Junghans P. (2001) Food web structure of the benthic community at the Porcupine Abyssal Plain (NE Atlantic): A stable isotope analysis. Progress in Oceanography 50: 383–4 10.1016/S0079-6611(01)00062-362-3 [DOI]
- Jamieson AJ, Gebruk A, Fujii T, Solan M. (2011) Functional effects of the hadal sea cucumber Elpidia atakama (Echinodermata: Holothuroidea, Elasipodida) reflect small-scale patterns of resource availability. Marine Biology 158: 2695–27 10.1007/s00227-011-1767-767-7 [DOI]
- Koehler R, Vaney C. (1905) An Account of the Deep-Sea Holothuroidea Collected by the Royal Indian Marine Survey Ship Investigator. The Indian Museum, Calcutta, 1–1 10.5962/bhl.title.17301730 [DOI]
- Lee S, Ferse S, Ford A, Wild C, Mangubhai S. (2017) Effect of sea cucumber density on the health of reef-flat sediments. Fiji’s Sea Cucumber Fishery: Advances in Science for Improved Management. Wildlife Conservation Society.
- Ludwig H. (1893) Vorläufiger Bericht über die erbeuteten Holothurien. In: Reports on the Dredging Operations off the West Coast of Central America to the Galapagos, etc., by the U. S. Fish Commission Steamer “Albatross”. IV. Bulletin of the Museum of Comparative Zoology at Harvard College 24(4): 105–114. [Google Scholar]
- Ludwig H. (1894) The Holothurioidea. In: Reports on an exploration off the west coasts of Mexico, Central and South America, and off the Galapagos Islands, in charge of Alexander Agassiz, by the U. S. Fish Commission Steamer “Albatross,” during 1891, Lieut. Commander Z. L. Tanner, U. S. N., commanding. XII. Memoirs of the Museum of Comparative Zoology at Harvard College 17(3): 1–183. [Google Scholar]
- Massin C, Hendrickx ME. (2010) A new species of deep-water Holothuroidea (Echinodermata) of the genus Synallactes from off western Mexico. Scientia Marina 74: 599–603. 10.3989/scimar.2010.74n3599 [DOI] [Google Scholar]
- Miller AK, Kerr AM, Paulay G, Reich M, Wilson NG, Carvajal JI, Rouse GW. (2017) Molecular phylogeny of extant Holothuroidea (Echinodermata). Molecular Phylogenetics and Evolution 111: 110–131. 10.1016/j.ympev.2017.02.014 [DOI] [PubMed] [Google Scholar]
- Morato T, Varkey DA, Damaso C, Machete M, Santos M, Prieto R, Santos RS, Pitcher TJ. (2008) Evidence of a seamount effect on aggregating visitors. Marine Ecology Progress Series 357: 23–32. 10.3354/meps07269 [DOI] [Google Scholar]
- Morato T, Hoyle SD, Allain V, Nicol SJ. (2010) Seamounts are hotspots of pelagic biodiversity in the open ocean. Proceedings of the National Academy of Sciences of the United States of America 107(21): 9707–9711. 10.1073/pnas.0910290107 [DOI] [PMC free article] [PubMed] [Google Scholar]
- O’Loughlin PM, Ahearn C. (2005) A review of pygal-furrowed Synallactidae (Echinodermata: Holothuroidea), with new species from the Antarctic, Atlantic and Pacific oceans. Memoirs of Museum Victoria 62: 147–179. 10.24199/j.mmv.2005.62.5 [DOI] [Google Scholar]
- O’Loughlin PM, Mackenzie M, VandenSpiegel D. (2013) New sea cucumber species from the seamounts on the Southwest Indian Ocean Ridge (Echinodermata: Holothuroidea: Aspidochirotida, Elasipodida, Dendrochirotida). Memoirs of Museum Victoria 70: 37–50. 10.24199/j.mmv.2013.70.04 [DOI] [Google Scholar]
- Östergren H. (1896) Zur Kenntnis der Subfamilie Synallactinae unter den Aspidochiroten. Festskrift for Lilljeborg, 345–360.
- Pitcher TJ, Bulman C. (2007) Raiding the larder: A quantitative evaluation framework and strophic signature for seamount food webs. In: Pitcher TJ, Morato T, Hart PJB, Clark MR, Haggan N, Santos RS. (Eds) Seamounts: Ecology, Fisheries, and Conservation.Blackwell, Oxford, UK, 282–295. 10.1002/9780470691953.ch14 [DOI]
- Roberts D, Moore HM, Berges J, Patching JW, Carton MW, Eardly DF. (2001) Sediment distribution, hydrolytic enzyme profiles and bacterial activities in the guts of Oneirophantamutabilis, Psychropoteslongicauda and Pseudostichopusvillosus: what do they tell us about digestive strategies of abyssal holothurians? Proceedings in Oceanography 50: 443–458. 10.1016/S0079-6611(01)00065-9 [DOI]
- Samadi S, Bottan L, Macpherson E, De Forges BR, Boisselier MC. (2006) Seamount endemism questioned by the geographic distribution and population genetic structure of marine invertebrates. Marine Biology 149: 1463–1475. 10.1007/s00227-006-0306-4 [DOI] [Google Scholar]
- Samyn Y, Vandenspiegel D. (2016) Sublittoral and bathyal sea cucumbers (Echinodermata: Holothuroidea) from the Northern Mozambique Channel with description of six new species. Zootaxa 4196: 451–497. 10.11646/zootaxa.4196.4.1 [DOI] [PubMed] [Google Scholar]
- Sars M. (1868) Om Afbildninger af nogle af hans son I forrige Aar ved Lofoten fundne Echinodermer og Coelenterater. Forhandlinger Videnskabs Selskabet, Christiania. 1867: 19–23. [Google Scholar]
- Solís-Marín FA. (2003) Molecular Phylogeny, Systematics and Biology of the Holothurian Family Synallactidae. Ph.D. thesis, University of Southampton, 356 pp. [Google Scholar]
- Solís-Marín FA. (2005) Synallacteslaguardai, a new species of sea cucumber from South Africa (Echinodermata: Holothuroidea: Synallactidae). Proceedings of the Biological Society of Washington 118: 570–575. 10.2988/0006-324X(2005)118[570:SLANSO]2.0.CO;2 [DOI]
- Solís-Marín FA, Caballero Ochoa A, Conejeros-Vargas C. (2024) Synallactesmcdanieli sp. nov., a new species of sea cucumber from British Columbia, Canada and the Gulf of Alaska, USA (Holothuroidea, (Synallactida). Biodiversity Data Journal 12: e124603. 10.3897/BDJ.12.e124603 [DOI] [PMC free article] [PubMed]
- Thandar AS. (2008) Additions to the holothuroid fauna of the southern African temperate faunistic provinces, with descriptions of new species. Zootaxa 1697: 1–57. 10.11646/zootaxa.1697.1.1 [DOI] [Google Scholar]
- Théel H. (1882) Report on the Holothuroidea dredged by H.M.S. ‘Challenger’ during the years 1873–76. Part I. Report on the Scientific Results of the Voyage of H.M.S. Challenger during the years 1873–1876. Zoology 4: 1–176. [Google Scholar]
- Théel H. (1886) Report on the Holothurioidea collected by H.M.S. Challenger during the Years 1873–76. Part II. Report on the Scientific Results of the Voyage of H.M.S. Challenger during the years 1873–76. Zoology 14: 1–290. [Google Scholar]
- Wagner D, Friedlander AM, Pyle RL, Brooks CM, Gjerde KM, Wilhelm TA. (2020) Coral reefs of the high seas: hidden biodiversity hotspots in need of protection. Frontiers in Marine Science 7: 2296–7745. 10.3389/fmars.2020.567428 [DOI] [Google Scholar]
- Walsh JHT. (1891) List of deep-sea holothurians collected during seasons 1887 to 1891, with description of new species. Natural History Notes from HM. Indian Survey Steamer INVESTIGATOR, Commander RF. Hoskyn, RN. commanding. No. 24. Journal of the Asiatic Society of Bengal 60: 197–204. [Google Scholar]
- Witbaard R, Duineveld G, Kok A, Van der Weele J, Berghuis EM. (2001) The response of Oneirophantamutabilis (Holothuroidea) to the seasonal deposition of phytopigments at the Porcupine Abyssal Plain in the Northeast Atlantic. Progress in oceanography 50(1–4): 423–441. 10.1016/S0079-6611(01)00064-7 [DOI] [Google Scholar]
- Worm B, Lotze HK, Myers RA. (2003) Predator diversity hotspots in the blue ocean. Proceedings of the National Academy of Sciences 100(17): 9884–9888. 10.1073/pnas.1333941100 [DOI] [PMC free article] [PubMed] [Google Scholar]
- WoRMS (2024a) Holothuroidea. https://www.marinespecies.org/aphia.php?p=taxdetails&id=123083 [accessed August 2024]
- WoRMS (2024b) Synallactidae Ludwig, 1894. https://www.marinespecies.org/aphia.php?p=taxdetails&id=123185 [accessed September 2024]
- Xu K. (2021) Exploring seamount ecosystems and biodiversity in the tropical Western Pacific Ocean. Journal of Oceanology and Limnology 39: 1585–1590. 10.1007/s00343-021-1585-9 [DOI] [Google Scholar]
- Yesson C, Letessier TB, Nimmo-Smith A, Hosegood P, Brierley AS, Hardouin M, Proud R. (2021) Improved bathymetry leads to> 4000 new seamount predictions in the global ocean–but beware of phantom seamounts! UCL Open Environment, 4: 03. 10.14324/111.444/ucloe.000030 [DOI] [PMC free article] [PubMed]
Associated Data
This section collects any data citations, data availability statements, or supplementary materials included in this article.
Supplementary Materials
Data Availability Statement
All of the data that support the findings of this study are available in the main text.