Synopiidae Dana, 1853 (Crustacea, Amphipoda) of the Clarion-Clipperton Zone

Lauren Elizabeth Hughes; Anne Helene Solberg Tandberg

doi:10.3897/zookeys.1274.141366

. 2026 Mar 24;1274:255–270. doi: 10.3897/zookeys.1274.141366

Synopiidae Dana, 1853 (Crustacea, Amphipoda) of the Clarion-Clipperton Zone

Lauren Elizabeth Hughes ¹, Anne Helene Solberg Tandberg ^2,³

PMCID: PMC13040243 PMID: 41929853

Abstract

The SynopiidaeAustrosyrrhoe hamptonaesp. nov. and Syrrhoe manowitzaesp. nov. are morphologically described from the Clarion-Clipperton Zone, Pacific Ocean. Their descriptions are supplemented by molecular barcodes. Both Austrosyrrhoe and Syrrhoe have been recorded from only a few specimens in previous studies. The ten specimens reported here add to the sparse understanding of the Synopiidae. Also remarkable is the depth range of both genera, occurring in shallow waters of ~50 m to depths of ~5000 m. Prior to this study, the known depth range was less than 3000 m for Austrosyrrhoe and 3500 m for Syrrhoe. In the Clarion-Clipperton Zone the new species Austrosyrrhoe hamptonaesp. nov. was collected at 5109 m and Syrrhoe manowitzaesp. nov. from 4368 m, providing a significant increase in the maximum recorded depths for these genera.

Key words: Austrosyrrhoe , deep-sea, depth range, North Eastern Pacific, Syrrhoe , taxonomy

Introduction

Austrosyrrhoe K.H. Barnard, 1925 is a little-known genus of five species with records spanning the breadth of the globe, species reports are only from the original descriptions and total 55 specimens for the genus (Table 1, Fig. 8). Austrosyrrhoe has been recorded from depths as shallow as ~58 m in the Irish Sea, and, prior to this study, the deepest record was 2700 m west of Greenland. Austrosyrrhoe is here reported from a depth of 5109 m in the Clarion-Clipperton Zone. Two Austrosyrrhoe species, A. crassipes K.H. Barnard, 1925 and A. fimbriatus (Stebbing & Robertson, 1891) have problematic type material (see remarks of A. hamptonae sp. nov.) and a limited original description. Yet the group remains distinct enough for modern descriptions to proceed in want of redescriptions, given the distinctiveness of the dorsal carination patterns across the group.

Table 1.

Distribution, Marine Ecoregions of the World (MEOW), and size range of world Austrosyrrhoe species.

Scientific name	Authority	Geographic area	MEOW provinces	MEOW realms	Size (mm)	Depth (m)
Austrosyrrhoe crassipes	K.H. Barnard, 1925	Cape Point, South Africa	Agulhas	Temperate southern Africa	4	1280
Austrosyrrhoe fimbriatus	(Stebbing & Robertson, 1891)	Firth of Clyde, Irish Sea, Scotland	North European Seas	Temperate Northern Atlantic	unknown	164
Austrosyrrhoe hamptonae	sp. nov.	Clarion-Clipperton Zone	Eastern Indo-Pacific	N/A	2.5–5.9	4352– 5109
Austrosyrrhoe kathleenae	Lörz & Coleman, 2013	New Zealand	Northern/Southern New Zealand	Temperate Australasia	5	1239
Austrosyrrhoe rinconis	J.L. Barnard, 1967	Baja California, USA	Warm Temperate Northeastern Pacific	Tropical Eastern Pacific	3	1205
Austrosyrrhoe septentrionalis	Stephensen, 1931	West Greenland, Iceland	Arctic/Northern Temperate Atlantic	Temperate Northern Atlantic	3	2702

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Figure 8. — Distribution map of world. A. *Austrosyrrhoe*; B. *Syrrhoe*.

In discussing the genus Austrosyrrhoe, J.L. Barnard (1972) acknowledged that the genus would benefit from more known species to understand the absence of the molar for placement in the broader family concept. The genus remains consistent for the shape of the gnathopods 1 and 2 propodus. Austrosyrrhoe has a relatively small body size (3–5 mm) with fine pereopods which break easily; specimens are most frequently collected as fewer than three individuals in samples. This may lead to the taxon being overlooked in deep sea ecological sampling.

The genus Syrrhoe Goës, 1866 includes 15 species; the current material from the Clarion-Clipperton Zone, S. manowitzae sp. nov., is the third species described from the north east Pacific, the other two being S. longifrons Shoemaker, 1964 and S. oluta J.L. Barnard, 1972 (Fig. 8). Pacific specimens are known from 150 to 4209 m depth, including the new species described here. Globally, Syrrhoe individuals are known from surface tows to depths of 4209 m. Eleven species are known from less than 800 m depth, with only four species, S. kareenae Lörz & Coleman, 2013, S. oluta, S. serrima J.L. Barnard, 1972, and S. manowitzae sp. nov., occurring below 1400 m. As well as an extensive depth range, body size has been recorded as ranging from 3.4 to 14 mm in Syrrhoe (Table 2).

Table 2.

Distribution, Marine Ecoregions of the World (MEOW), and size range of world Syrrhoe species.

Scientific name	Authority	Geographic area	MEOW provinces	MEOW realms	Size (mm)	Depth (m)
Syrrhoe affinis	Chevreux, 1908	Morocco, North Atlantic Coast	Lusitanian	Temperate Northern Atlantic	7	851
Syrrhoe angulipes	Ledoyer, 1977	Marseille, France	Lusitanian	Temperate Northern Atlantic	3.5	360
Syrrhoe anneheleneae	Fuchs, Coleman & Lörz, 2019	Spitsbergen, Norway	North European Seas	Temperate Northern Atlantic	9	579
Syrrhoe crenulata	Goës, 1866	Spitsbergen, Norway	North European Seas	Temperate Northern Atlantic	10	742
Syrrhoe kareenae	Lörz & Coleman, 2013	off Oates Land, Ross Sea, Antarctica	Ross Sea, Continental High Antarctic	Southern Ocean	9	1645
Syrrhoe longifrons	Shoemaker, 1964	Georges Channel, Vancouver Island, Canada	Cold Temperate North East Pacific	Temperate North Pacific	10	150
Syrrhoe manowitzae	sp. nov.	Clarion-Clipperton Zone	Eastern Indo-Pacific	N/A	5.5– 20	4185–4368
Syrrhoe nodulosa	K.H. Barnard, 1932	Admiralty Bay, Palmer Archipelago, South Shetland Islands	Scotia Sea	Southern Ocean	14	500
Syrrhoe oluta	J.L. Barnard, 1972	Columbia and Oregon, United States	Cold Temperate North East Pacific	Temperate Northern Pacific	7	3251
Syrrhoe papyracea	Stebbing, 1888	Culebra Island, West Indies, Caribbean Sea	Tropical Northwestern Atlantic	Tropical Atlantic	13	713
Syrrhoe petitaserrata	Hughes, 2009	Great Barrier Reef, Queensland, Australia	Northeast Australian Shelf	Central Indo-Pacific	3.4	0
Syrrhoe psychrophila	Monod, 1926	Bellingshausen Sea, Antarctica	Amundsen/Bellingshausen Sea, Continental High Antarctic	Southern Ocean	7.8	400
Syrrhoe sadiae	Lörz & Coleman, 2013	Tasman Sea and South Pacific New Zealand	Northern New Zealand	Temperate Australasia	8.5	770
Syrrhoe semiserrata	Stebbing, 1888	off Melbourne, Victoria, Australia	Southeastern Australian Shelf	Temperate Australasia	7.6	60
Syrrhoe serrima	J.L. Barnard, 1972	off Argentina 40 South	Magellanic	Temperate South America	5.8	1475
Syrrhoe tuberculata	Dahl, 1954	Discovery Inlet, Ross Sea	Ross Sea, Continental High Antarctic	Southern Ocean	unknown	550

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Materials and methods

The material for the present study was sampled in the central Eastern Pacific, specifically in the easternmost sector of Clarion-Clipperton Zone (CCZ). The material was collected with epibenthic sledge (EBS) or multi-corer during four scientific deep-sea cruises: the ABYSSLINE-2 (ABYSSal baseLINE project) in 2015, MANGAN 2018, MANGAN 2023, and NORI-D 2021. For details of gear deployment and sample processing, see Jażdżewska and Horton (2026) and Jażdżewska et al. (2025). Samples used in this study were preserved in 80% ethanol. Material is lodged at the Senckenberg Natural History Museum (Frankfurt, Germany; SMF) and the Natural History Museum (London, United Kingdom; NHMUK). All the remaining material is kept at the Deutsches Zentrum für Marine Biodiversitätsforschung (Wilhelmshaven, Germany; DZMB).

Individuals were initially examined using either a Leica M125 or a Nikon SMZ800 stereomicroscope.

Specimens were dissected in 80% ethanol, and microscope slides were made with Polyvinyl Lactophenol or Aquatex mounting agent. Illustrations were made using a Nikon SMZ 800 (whole animal) stereomicroscope and a Nikon Eclipse 50i compound microscope fitted with a camera lucida. The habitus of Austrosyrrhoe hamptonae sp. nov. is additionally imaged using a confocal laser scanning microscope (CLSM). The holotype was stained in Congo red and acid fuchsin, temporarily mounted onto slides with glycerine, and examined with a Leica TCS SPV equipped with a Leica DM5000 B upright microscope and three visible-light lasers (DPSS 10 mW 561 nm; HeNe 10 mW 633 nm; and Ar 100 mW 458, 476, 488, and 514 nm), combined with the software LAS AF v. 2.2.1 (Leica Application Suite, Advanced Fluorescence). A series of photographic stacks were obtained, collecting overlapping optical sections throughout the whole preparation (Michels and Büntzow 2010; Kamanli et al. 2017).

Standard abbreviations on the plates are: A, antenna; G, gnathopod; H, head; LL, labium; Md, mandible; Mx1, maxilla 1; Mx1 P, maxilla 1 palp; Mx2, maxilla 2; Mxp, maxilliped; P, pereopod; T, telson; U, uropod; UL, labrum; L, left; R, right. Distributions in Table 1 are by geographic region following Spalding et al. (2007) for Marine Ecoregions of the World (MEOW).

All individuals were subjected to cytochrome c oxidase subunit I gene (COI) barcoding prior to identification of the species. The molecular procedures are described in Jażdżewska et al. (2025). All sequences were deposited in GenBank with the accession numbers PQ734342, PQ734362, PQ734459, PQ734493, PQ734518, PQ734598, PQ734626, PQ734672, PQ734768, and PZ022426. The relevant voucher information, taxonomic classifications and sequences are deposited in the data set “DS-AMPHICCZ” in the Barcode of Life Data System (BOLD) (https://doi.org/10.5883/DS-AMPHICCZ) (Ratnasingham and Hebert 2007).

Systematics

Family Synopiidae Dana, 1853

Genus Austrosyrrhoe K.H. Barnard, 1925

Austrosyrrhoe hamptonae sp. nov.

1F4E481E-1F83-59F8-9421-9465E3326823

https://zoobank.org/D1879238-1B9C-4A43-B838-60A35DDF322A

Figs 1 , 2 , 3 , 8

Figure 1. — *Austrosyrrhoe* *hamptonae* sp. nov. A. microscope photograph of holotype, female, 5.9 mm, *SMF* 63342; B. CLSM photograph of holotype, female, 5.9 mm, *SMF* 63342; C. habitus of paratype, male, size undetermined, *SMF* 63343.

Figure 2. — *Austrosyrrhoe* *hamptonae* sp. nov. Mxp, holotype, female, 5.9 mm, *SMF* 63342, all other appendages paratype, size undetermined, *SMF* 63343, Clarion-Clipperton Zone. Scale bar: 0.1 mm.

Figure 3. — *Austrosyrrhoe* *hamptonae* sp. nov. G1, G2, P3–5, holotype, female, 5.9 mm, *SMF* 63342; paratype, size undetermined, P4 L, *SMF* 63343, Clarion-Clipperton Zone. Scale bar: 0.5 mm.

Type material.

Holotype: Pacific Ocean • female, 5.9 mm, Clarion-Clipperton Zone; BGR exploration contract area, R/V Sonne, MANGAN 2018, EBS, SO 262-155, 9 May 2018, 11°47.436'N, 117°32.213'W – 11°47.677'N, 117°30.910'W, 4352–4351 m, SMF 63342, COI: PQ734768. Paratypes: Pacific Ocean • juvenile, 2.5 mm, Clarion-Clipperton Zone; BGR exploration contract area, R/V Kilo Moana, MANGAN 2023, EBS, KM23-69, 4 May 2023, 11°36.252'N, 118°02.981'W – 11°37.1050'N, 118°01.2511'W, 4368–4356 m, SMF 63344, COI: PQ734518 • male, size undetermined, Clarion-Clipperton Zone, BGR exploration contract area, R/V Kilo Moana, MANGAN 2023, EBS, KM23-7, 17 Apr 2023, 12°02.2976'N, 138°05.4932'W – 12°03.5888'N, 138°05.7092'W, 5109–5139 m, SMF 63343, COI: PQ734493.

Other material.

Pacific Ocean • unsexed (head only), not measured, Clarion-Clipperton Zone; BGR exploration contract area, R/V Kilo Moana, MANGAN 2023, EBS, KM23-69, 4 May 2023, 11°36.252'N, 118°02.981'W – 11°37.1050'N, 118°01.2511'W, 4368–4356 m, DSB_8459, COI: PQ734598.

Diagnosis.

Gnathopods 1–2 propodus palm defined by serrate robust seta. Pereopod 3 coxa anterodistal lobe produced subovate, posterodistal lobe absent. Pereopods 5–6 basis subovoid. Pleonites 1–3 posterodistal margin smooth with single acute convex dorsal margin, with posterior minute dorsal process. Epimera 1–3 posterior margin concave, posterodistal corner with small acute tooth. Urosomite 1 dorsal margin smooth with small acute dorsal process. Urosomite 2 dorsal margin smooth with acute process directed posteriorly. Urosomite 3 posterior margin with setal fringe.

Description.

Head (Figs 1, 2) not protuberant; rostrum long, directed ventrally, apically acute; lateral cephalic lobe subtriangular; eyes unknown; accessory eyes unknown. Antenna 1 unknown. Antenna 2 flagellum more than 7-articulate, broken. Mandible palp article 2 with many slender setae; article 3 with many slender apical setae; right lacinia mobilis 3 dentate; molar greatly enlarged, smooth, not triturative, accessory setal row with two setae on left. Maxilla 1 inner plate unknown, outer plate with nine robust setae, palp article 2 with three apical robust setae. Maxilliped not foliaceous.

Pereon (Figs 1, 3). Pereonites 1–7 dorsal margin smooth, without lateral ridge. Gnathopod 1 subchelate; coxa anterior margin produced, rounded, not tapering distally; basis length subequal to carpus; propodus palm subacute/oblique, defined by serrate robust seta; dactylus well developed, with posterior margin with several teeth. Gnathopod 2 subchelate; coxa not distally tapering; basis longer than carpus; propodus palm subacute/oblique, defined by one serrate and one smooth robust seta; dactylus well developed, posterior margin with one tooth. Pereopod 3 pelagont (dominant over coxa 4), coxa anterodistal lobe produced subovate, posterodistal lobe absent. Pereopod 4 coxa smaller than coxa 3, lobate in shape, with well-developed posteroventral lobe half the depth of the posterior margin. Pereopods 5 and 6 bases subovoid, posterodistal lobe not extending below ischium, posterior margin broadly serrate. Pereopod 5 basis posterior margin weakly subquadrate.

Pleon (Figs 1, 2). Pleonites 1–3 posterodistal margin smooth with single acute, convex dorsal margin, with posterior minute dorsal process. Epimera 1–3 posterior margin concave, posterodistal corner with small acute tooth. Urosomite 1 dorsal margin smooth with small acute dorsal process. Urosomite 2 dorsal margin smooth with acute process directed posteriorly. Urosomite 3 posterior margin with setal fringe. Uropod 3 length exceeding uropods 1 and 2; peduncle long, length twice breadth. Telson length more than two times breadth (broken), longer than uropod 3 peduncle, moderately cleft along 1/3 length, without setae along the lateral margin, apical setae unknown.

Etymology.

Named for Jacqueline B. Hampton, who illustrated amphipods of the north eastern Pacific from the Cedros Trench and offshore of the Columbia River, Oregon, in the 1960s and 1970s publications of Jerry Barnard.

Molecular identification.

Following the definition given by Pleijel et al. (2008), the sequence of the holotype male of Austrosyrrhoe hamptonae sp. nov. (SMF 63342, GenBank accession number PQ734768) is designated as a hologenophore of all obtained sequences. The sequences of the paratypes and non-type collection of the species are deposited in GenBank with the following accession numbers: PQ734493, PQ734518, PQ734598. The species has also received a Barcode Index Number from Barcode of Life Data Systems: BOLD:AEB6000 (https://doi.org/10.5883/BOLD:AEB6000).

Remarks.

Austrosyrrhoe hamptonae sp. nov. can be separated from other species in the genus by the urosomite dorsal carination pattern, with urosomite 1 dorsal margin smooth with a small acute tooth, urosomite 2 dorsal margin with an acute process, and urosomite 3 posterior margin with a setal fringe.

Austrosyrrhoe hamptonae sp. nov. and A. fimbriatus (Stebbing & Robertson, 1891) both have the urosomite 3 posterodorsal margin lined with a setal fringe. Austrosyrrhoe hamptonae sp. nov. can be separated from A. fimbriatus and A. septentrionalis Stephensen, 1931 by the pereopods 5 and 6 bases being subovate in A. hamptonae sp. nov. and more subquadrate-rectilinear in the latter species.

Austrosyrrhoe rinconis J.L. Barnard, 1967 is reported from nearby Baja California (1095–1205 m), while the remaining four species are in the North Atlantic, South Atlantic, and South Pacific Ocean (Fig. 7). Austrosyrrhoe hamptonae sp. nov. has the coxa 3 anterior distal corner rounded while in A. rinconis the corner is acute.

Figure 7. — *Syrrhoe* *manowitzae* sp. nov., holotype, female, 20 mm, *NHMUK* 2025.2873. Scale bar: 1 mm.

Austrosyrrhoe hamptonae sp. nov., A. crassipes K.H. Barnard, 1925, and A. kathleenae Lörz & Coleman, 2013 have a single serrate palm defining setae on gnathopods 1 and 2, while A. septentrionalis has gnathopods 1 and 2 with two setae defining the palm and in A. fimbriatus the palm-defining setae are simple.

A search of the NHM collection for the comparative type material of A. fimbriatus concluded the material is lost. Previous work by J.L. Barnard (1972) stated the type specimens of A. crassipes were in poor condition and beyond repair to properly diagnose the genus.

Prior to the current study, the deepest record of Austrosyrrhoe was A. septentrionalis at 2702 m near Greenland. The material of A. hamptonae from depths of 4352–5109 m in the Clarion-Clipperton Zone, Pacific Ocean increases this by more than 2409 meters.