Stegophiura waltersi, O’Hara & Thuy, 2025

O’Hara, Timothy D. & Thuy, Ben, 2025, Seamount ophiuroids from the High Seas of the western Indian Ocean, Zootaxa 5718 (1), pp. 1-88 : 33-37

Stegophiura waltersi sp. nov.

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Fig. 11–12

TYPE LOCALITY. Walters shoal, Plaine Sud, 33° 48.82´S, 44° 5.9699´E to 33° 51.8´S, 44° 4.72´E, 1539–1615 m

TYPE MATERIAL. — MD208 : stn CP4913, Walters shoal, Plaine Sud, 33° 48.82´S, 44° 5.9699´E to 33° 51.8´S, 44° 4.72´E, 1539–1615 m, 11/5/2017, holotype: 1 ( MNHN IE.2023.4069); paratypes: 27 ( MNHN IE.2016.1375) ( DNA code= IE.2016.1375) .

OTHER STUDY MATERIAL. — MD208 : stn CP4914, Walters shoal, Plaine Sud, 33° 51.1´S, 44° 4.8999´E to 33° 54.73´S, 44° 3.2199´E, 1598–1714 m, 11/5/2017: 258 ( MNHN IE.2016.1374) ( DNA code= IE.2016.1374) . — MD208 : stn CP4915, Walters shoal, Plaine Sud, 33° 56.85´S, 44° 0.07´E to 33° 58.8´S, 43° 55.3999´E, 1865–2058 m, 12/5/2017: 191 ( MNHN IE.2016.1363) ( DNA code= IE.2016.1363-2) .

COMPARATIVE MATERIAL EXAMINED. Amphiophiura distincta ( Koehler, 1904) : SBD/825 S, Great Barrier Reef Seabed Survey , 18° 22.033´S, 147° 16.8289´E to 18° 22.107´S, 147° 17.0129´E, 74.4– 73.7 m, 19/9/2003 , MTQ SBD001284 ( DNA code= SBD001284 ). SS10/2005/26, Albany , 35° 20.382´S, 118° 20.46´E to 35° 20.682´S, 118° 19.74´E, 212–213 m, 23/11/2005 , MV F112578 ( DNA code=F112578). Stegophiura lapidaria ( Lyman, 1878) : Challenger /235, off Hamamatsu, 34° 7´N, 138° 0´E, 1050 m, 4/6/1875, holotype , NHMUK 1882.12 .23.412. BIOPAPUA/CP3759, Au large de Feni Islands, 4° 0´S, 153° 36´E, 287–352 m, 14/10/2010 , MNHN IE.2007.2942 ( DNA code=BP57). Stegophiura rhabdotoplax Murakami, 1942 : EXBODI/DW3876, Ile Matthew-Volcan nord, 22° 17.2´S, 171° 17.6´E, 518–833 m, 17/9/2011 , MNHN IE.2007.7273 ( DNA code=IE.2007.7273). Stegophiura sp. MoV.7272 IN2021_ V04 /26, Max Seamount , 11° 42.608´S, 107° 1.9122´E to 11° 42.92´S, 107° 3.459´E, 1915– 1990 m, 10/7/2021 , identified by O’Hara (2024b), MV F305618 ( DNA code=F305618). Stegophiura vivipara Matsumoto, 1915 : Sagami Bay , off Misaki, 35° 7.746´N, 139° 34.255´E to 35° 8.033´N, 139° 34.057´E, 94.5–96.6 m, 31/5/2018 , MV F248380 ( DNA code=Misaki002) .

Diagnosis. Disc with rounded imbricating disc scales and polygonal radial shields that are contiguous for their distal half. Genital granules hemispherical near the oral shield, becoming conical near margin and spiniform as arm comb papillae. Oral shields wider than long, trilobed. Arms rounded, DAPs and VAPs becoming separate after basal 5 plates, lacking mid-ventral ridge on basal VAPs. 3 conical arm spines, to 0.5 segments in length, no accessory plate-like arm spines.

Description. Holotype 12 mm dd, disc pentagonal, thick; largest arm fragment 30 mm long. Disc covered with rounded imbricating scales, with radiating patterns of stereom, primary plates and interradial scales largest, surrounded by smaller plates, 3 plates between radial shields interradially, marginal interradial plate not larger than other scales; radial shields longer than wide, irregularly hexagonal, with an acute to rounded angle proximally, an obtuse angle distally, and contiguous radially for half their length; scales smaller ventrally, 3 transverse and 6–7 longitudinal rows; hemispherical papillae along genital slit from oral shield, becoming cone-shaped to spine-like and separate near margin and onto the dorsolateral surface; an opposing comb of small spines occurs along the outer edge of the first DAP and first free LAP. Oral shields bilobed, with a large rounded distal lobe, 2x wider than long, and smaller inner lobe, just wider than long, with an obtuse inner angle and straight to slightly concave lateral sides; adoral shields narrow, curve around the inner lobe of the oral shields and slightly expanded distally, contiguous interradially and separated radially by the first VAP; visible section of the oral plates parallelogram in shape, 2x as wide as long, contiguous interradially, and slightly concave distally where it is incised by the 2nd oral tentacle pore; 5 lateral oral papillae, rounded and taller than wide proximally becoming low and wide distally; ventral tooth ovoid with a blunt terminal edge; 2nd oral tentacle pore with 5 abradial scales (adoral shield spines) which are widest distally, and 4 adradial scales, the distal two arise from the first VAP and inner two from the triangular ventral compartment plate that borders the distal section of the jaw slit.

Arms oblong-shaped in cross-section; first DAP very thin triangular just visible distal to the radial shields, 2nd DAP 2.3x as wide as long, hexagonal, 2nd DAP 1.75x as wide as long, becoming narrower from the 3rd, kite-shaped from the 5th, and separate from the 8th DAP, with minute spinous processes distally; LAPs higher than long, obtusely pointed dorsally, beaded/perforated. First VAP irregular hexagonal, 2x as wide as long, widest distally, with a truncate proximal edge and a slightly concave distal edge, contiguous with succeeding plate, 2nd VAP as long as wide, gradually attenuating proximally, 3rd similar except it has notable transverse striations, becoming kite-shaped by the 5th VAP, smaller and separated from the 6th, wider than long by the 8th VAP. Three cone-shaped to spiniform arm spines, to 1/2 segment in length near arm base, widely separated, with the middle spine slightly closer to the ventral than dorsal spine, middle spine shorter and hooklet-shaped on distal segments with an abradially bent apex and no secondary teeth; no smaller accessory arm spines (except opposing arm comb on first free LAP). Tentacle pore adjacent to 2nd and 3rd VAP with 4–5 abradial (on LAP) and 3–4 adradial (on VAP) scales, the inner adradial scale enlarged, 4 abradial and 4 adradial ones by the 5th VAP; adradial scales cease by 8–9th VAP. Colour (live and preserved) light brown ( Fig. 6f ).

Paratypes 5–12 mm dd, sometimes lower arm spine duplicated, preserved colour on some specimens notably darker brown than the holotype. Vertebrae ( Fig. 12a–d ) zygospondylous, with high dorsal and well-developed ventral fossae, narrow ventral groove and tall narrow zygosphene; LAPs ( Fig. 12e–f ) with densely perforated exterior stereom, simple round arm spine articulations for muscle attachment and small adjacent neural perforations; DAPs ( Fig. 12j ) kite-shaped with denticulate distal edge; oral plates ( Fig. 12g –h ) long, distal and proximal sections fused, 2nd oral tentacle pore exiting outside of jaw slit; dental plate ( Fig. 12i ) 2x as tall and wide; teeth and infradental papillae perforations small; five teeth in vertical series ( Fig. 11e ), 3rd to 4th (from ventral) chisel like, widened at tip, dorsal tooth spine-like; tentacle scales ( Fig. 12l ) with angled spinous apical edge; arm spines ( Fig. 12m ) with longitudinal grooves in the stereom on the apical section; abradial genital scale smaller and wider than adradial plate ( Fig. 12n–p ).

Distribution. Walters Shoal ( 1539–2058 m).

Remarks. Molecular evidence places this species within the genus Stegophiura . Two characters tend to characterise Stegophiura species, the presence of small scale-like accessory arm spines between the longer pointed ones, and/or the presence of a swollen mid-radial ridge on basal VAPs. The following species possess accessory arm spines: S. nodosa type species (see Djakonov 1954, fig. 28), S. brachyactis (H.L. Clark, 1911) , S. carinata Djakonov, 1954 , S. hainensis Liao, 1995 , S. ponderosa ( Lyman, 1878) , S. rhabdotoplax , S. sladeni ( Duncan, 1879) , S. sterea H.L. Clark, 1908 , S. sterilis Koehler, 1922a and S.wilhelmi Manso, 2010 . In addition, re-examination of the unique holotype of Amphiophiura lapidaria revealed a series of flat rounded papilla-like accessory arm spines on the LAPs, 7 between the dorsal and middle arm spine, and 2 between the middle and ventral spine, and on this basis (confirmed by DNA evidence, Fig. 2a ) this species is transferred to the genus Stegophiura . It is unclear from Duncan’s (1879) type description of S. striata whether it has dimorphic arm spines or not. Species that have swollen ridges on the basal VAPs include S. nodosa (Lütken, 1855) , S. carinata , S. elevata ( Lyman, 1878) , S. hainensis , S. macrantha H.L. Clark, 1915 , S. singletoni McKnight, 1975 , S. sladeni , and S. stuwitzii (Lütken, 1857) . Only two existing species appear to lack both of these characters: S. sculpta from Korea-Japan and S. vivipara from Japan. These are very similar and possibly synonymous. Both are reported to be viviparous ( Murakami 1941, Matsumoto 1917 respectively). Our DNA sample of S. vivipara from Japan was phylogenetically placed in a separate evolutionary lineage that also contains Amphiophiura distincta . All three species are characterised by the very short arms (to 2x dd) and few disc plates. Consequently, we consider S. sculpta and S. vivipara to be Amphiophiura species, pending a revision of that genus.

Stegophiura waltersi sp. nov. also does not have accessory arm spines nor swollen ventral arm plates. However, it is otherwise morphologically and genetically very close to S. lapidaria , sharing the same oral frame, arm plates, and radial shields. Stegophiura lapidaria differs in having a pentagonal centrodorsal plate, no smaller plates around the primaries, and the accessory arm spines. We consider the lack of accessory arm spines on our new species as a derived character. A related undescribed lineage ( Stegophiura sp. MoV.7272) that also lacks accessory arm spines occurs on seamounts in the eastern Indian Ocean ( O’Hara 2024b).

Amphiophiura radiata is superficially similar but can be distinguished by its square genital papillae and an enlarged plate at the interradial margin.

Etymology. Named after the Walters Shoal seamount.

Figures

FIGURE 2. Maximum likelihood phylogeny of the ophiuroid samples from JC066 and MD208 expeditions and comparative specimens. The phylogeny was created from 275 kb of nuclear DNA and 1431 bp of mitochondrial COI using RAxML v.8.1.20 47 GTRCAT model with 4 partitions (3 exon codon positions and COI) and converted to a chronogram using TreePLv1.0 and 11 fossil-based calibration points. Green samples are from Walters Shoal, blue samples from Coral, purple from Melville, and red samples from Atlantis Bank. Node labels are RAxML fast-bootstrap values (n=100). The tip labels are composed of the species name, sample code, bp of nuclear (415 genes) and mitochondrial (COI) DNA, geographic and depth distribution. Geographic codes:AN=Antarctic, AR=Arctic, AU=S Australia, EA=E Atlantic, EP=E Pacific, IN=Indian, IP=Indo-Pacific, NA=N Atlantic, NEP=NE Pacific, NWP=NW Pacific, NZ=New Zealand, SA=S Africa, SK=Kerguelen, SM=S America, WA=W Atlantic; depth codes: S=Shelf, B=Bathyal, A=Abyssal. (a) the orders Euryalida and Ophiurida, (b) Ophiacanthida and Ophioscolecida, (c) Amphilepidida and Ophioleucida.

FIGURE 6. Ophiopyrgus hainesae sp. nov. holotype MNHN IE.2023.4001 (a) dorsal view, (b) dorsal view enlarged, (c) arm base, lateral view, (d) dorsolateral view, (e) ventral view. (f) Ship-board photo of MD208 catch CP4914, with the species: Oh = Ophiopyrgus hainesae, Oa = Ophioplinthus abyssorum, Om = Ophiomyces delata, Sw = Stegophiura waltersi.

FIGURE 11. Stegophiura waltersi sp. nov. holotype MNHN IE.2023.4069 (a) dorsal view, (b) ventral view, (c) dorsal arm tips, (d) arm base, lateral view; paratype MNHN IE.2016.1375 (e) two jaws, lateral view (SEM), (f) arm, dorsal view (SEM), (g) arm, lateral view (SEM, some arm spines missing), (h) ventral disc (SEM), (i) arm, ventral view (SEM).

FIGURE 12. Stegophiura waltersi sp. nov. paratype MNHN IE.2016.1375 (a) vertebra, proximal view, (b) vertebra, distal view, (c) vertebra, proximal view, (d) vertebra, ventral view, (e) lateral arm plate, distal view, (f) lateral arm plate, lateral view, (g) oral plate, interradial view, (h) oral plate, radial view, (i) dental plate, (j) dorsal arm plate, (k) ventral arm plate, (l) tentacle scale, (m) arm spine, (n–o) opposite faces of adradial genital plate, (p) abradial plate, (q) radial shield, (r) centrodorsal plate.