Ophiomyxa pedicula, O’Hara & Thuy, 2025

Ophiomyxa pedicula sp. nov.

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Fig. 24d–g View FIGURE 24 , 25f–j View FIGURE 25

TYPE LOCALITY. Walters Shoal, Pentes, 33° 8.7´S, 43° 58.16´E GoogleMaps to 33° 8.77´S, 43° 59.13´E, 492–588 m

TYPE MATERIAL. — MD208 : stn DW4890, Walters Shoal, Pentes, 33° 8.7´S, 43° 58.16´E to 33° 8.77´S, 43° 59.13´E, 492–588 m, 4/5/2017, holotype: 1 ( MNHN IE.2016.1062) ( DNA code= IE.2016.1062) GoogleMaps .

COMPARATIVE MATERIAL EXAMINED. Ophiomyxa pedicula SAYA /DW5411, N Saya de Malha , 9° 49.812´S, 60° 45.455´E to 9° 49.759´S, 60° 45.569´E, 216– 192 m, 7/11/2022, MNHN GoogleMaps IE.2023.4245 ( DNA code= IE.2023.4245). Ophiostiba sp. MoV.7274 SOL 5117/044BS026, Bonaparte Gulf, 10° 27.123´S, 129° 31.439´E to 10° 27.144´S, 129° 31.476´E, 55.2–55.7 m, 16/8/2010 GoogleMaps , MV F173909 ( DNA code=F173909) .

Diagnosis. Disc covered in a thick pulpy skin, no marginal row of disc plates, short (2 arm segments long) genital slits, 3 flattened oral papillae with a denticulate margin, Five arms, arms and spines covered in thick skin, 1 (sometimes 2) thin ovoid fenestrated DAPs on each segment, VAPs longer than wide, with prominent distal notch and distolateral ‘wings’, 2–3 arm spines on each side, alternating on different segments, less than a segment in length, with lateral thorns, no tentacle scale, but tube feet strengthened by a pair of elongate plates.

Description. Holotype 10 mm dd, arms 40+ mm long; disc pentagonal, covered in a thick pulpy skin that obscures any embedded plates, radial shields apparently bar-like widely separate, no discernible series of margin plates between radial shields; genital slits short, 2 arm segments long; Oral shields rounded triangular, with a slightly convex distal edge and rounded angles, wider than long, adoral shields long and thin, extending around the lateral angles of the oral shields, meeting interradially, separated radially by the small 1st VAP; 5 teeth, thin with a denticulate glassy edge, ventral 4 are rounded, dorsalmost (inner) tooth longer and spatulate; 3 oral papillae, wide, with a rounded to truncate outer edge, also finely denticulate and glassy; both pairs of oral tentacles emerge within slit.

Five arms, arms and spines covered in thick skin, DAPs thin and fenestrated, in 1–2 pieces, ovoid to irregular in shape, just separated, sometimes appear to be split at mid-length (but this could be an artefact), do not hide the dorsal wings of the underlying vertebrae; LAPs ventrolateral, ventral flanges meet on the midline, plate longer where the arm spines articulations are present; overlain and separated longitudinally by the VAPs; VAPs longer than wide, with prominent distolateral ‘wings’ with pointed distal angles, distal margin deeply v-shaped, rounded proximolaterally around the tube foot, with an obtuse angle proximally, widest just distal to the tentacle pores; one arm spine on first 2 segments, 2 on next 2 segments, 2–3 arm spines on succeeding proximal segments, alternating on successive segments, then becoming regularly 3 spines from mid-arm, uppermost longest, less than a segment in length, proximal arm spines with thorns, distal arm spines more hook-like with 2 teeth and a wide opaque pedicel; no tentacle scales, but tube feet strengthened by a pair of elongate plates on either side. Colour pale with some remnant darker markings on the dorsal side of the arm, perhaps indicating some banding when alive.

Ossicles. Arm spine articulations round to oval with a central muscle perforation and a smaller ventrodistal nerve opening; arm spines when stripped of skin have a large vase-shaped opaque basal pedicel, supporting a glassy ridged spine, with notable denticulations on the ventral and to a lesser extent dorsal side of the upper half of the spine. Vertebrae zygospondylous, with large muscle fossae dorsolaterally, and a groove along the dorsal midline that can be seen under the DAPs.

Distribution. Walters Shoal ( 492–588 m), Saya de Malha Bank ( 192–216 m)

Remarks.The denticulate oral papillae and teeth clearly identify this species as an Ophiomyxa .The unfragmented DAPs indicate a relationship to the O. vivipara-serpentaria complex, as DAPs are present as numerous fragmented pieces in most species. Also, both O. vivipara and O. serpentaria have elongated ossicles in the sheaf around the tube feet similar to the new species. Our phylogeny also places the new species close to the O. vivipara-serpentaria complex. However, the new species appears to lack the row of disc scales that connect the radial shields in O. vivipara-serpentaria (see Mortensen, 1933d) as well as many other Ophiomyxa species. Ophiohyalus gotoi Matsumoto, 1915 from Japan also has unfragmented DAPs, and may be related. The type differs in having DAPs that are figured as being separate from each other, a row of disc scales that border the disc, and curved arm spines ( Matsumoto, 1917).

A specimen from Saya de Malha Bank is molecularly and morphologically similar to the MD 208 specimen and is referred to the new species. It measures 9 mm dd, the long arms have slender tips, the arms covered in thick skin around the vertebrae, especially distally, three pointed skeletal arm spines (in thick skin) upper one hook-like at very arm tip, the row of marginal disc plates appears to be lacking, there are 3–4 small serrated oral papillae.

The next nearest specimen on our phylogeny is a 6-armed specimen from Western Australia. It also has DAPs that are entire, and the wide rounded oral papillae and teeth have denticulations. The 3 arm spines have thorns in annulations around the spine flank. The only described ophiomyxid species with 6-arms is Ophiostiba hidekii Matsumoto, 1915 also from Japan. The type is small ( 3.5 mm dd) but differs from the new species in having 6 arms, being fissiparous, lacking DAPs and having 4–5 oral papillae are simple and triangular, lacking denticulations, and having a marginal row of disc scales ( Matsumoto, 1917). More research is needed to clarify the relationships of these species.

The other SWIO species can be distinguished from O. pedicula as follows: O. tenuispina has fragmented DAPs, O. neglecta has 4 oral papillae, and O. vivipara has a row of disc scales around the margin. The arm ossicles also differ: the VAPs are typically wider in other species with a less pronounced distal notch, and the arm spines have a less widened base with smaller thorns near the tip ( Fig. 25 View FIGURE 25 ).

Etymology. Named after the large vase-shaped pedicel on the arm spines.