Ophiosabine multifida, O’Hara & Thuy, 2025

Ophiosabine multifida sp. nov.

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Fig. 16h–j View FIGURE 16 , 17 View FIGURE 17

TYPE LOCALITY. Atlantis Bank, 32° 42.658´S, 57° 16.371´E GoogleMaps to 32° 42.64´S, 57° 17.58´E, 707 m

TYPE MATERIAL. — JC066 : stn 8-3, Atlantis Bank, 32° 42.658´S, 57° 16.371´E to 32° 42.64´S, 57° 17.58´E, 707 m, 9/12/2011, holotype: 1 ( NHMUK 2025.50 About NHMUK ) GoogleMaps ; paratype: 1 ( MV F321041 ) ( DNA code= JC066-3612 ) ; paratype: 1 ( NHMUK 2025.49 About NHMUK ) ; paratype: 1 ( NHMUK 2025.48 About NHMUK ) ; paratype: 1 ( NHMUK 2025.47 About NHMUK ) ; paratype: 1 ( NHMUK 2025.51 About NHMUK ) ; paratype: 1 ( NHMUK 2025.52 About NHMUK ) .

OTHER STUDY MATERIAL. — JC066 : stn 4-37, Coral seamount, 41° 21.7673´S, 42° 54.9067´E to 41° 22.4´S, 42° 54.6´E, 740 m, 20/11/2011: 1 ( NHMUK 2025.46 About NHMUK ) ( DNA code= JC066-1252 ). — JC066: stn 8-4, Atlantis Bank, 32° 42.43´S, 57° 16.48´E to 32° 42.17´S, 57° 14.42´E, 800 m, 10/12/2011: 1 ( NHMUK 2025.53 About NHMUK ) ( DNA code= JC066-4303 ). — JC066: stn 8-5, Atlantis Bank, 32° 42.862´S, 57° 14.666´E to 32° 43.3´S, 57° 15.2´E, 828– 994 m, 10/12/2011: 1 ( NHMUK 2025.54 About NHMUK ) GoogleMaps .

COMPARATIVE MATERIAL EXAMINED. Ophiosabine acanthinotata (H.L. Clark, 1911) : Rinkai /120110(D-105)st1, Sagami Bay, 35° 6.101´N, 139° 34.284´E to 35° 6.684´N, 139° 34.061´E, 218–318 m, 10/11/2012 GoogleMaps , NSMT E11758 View Materials ( DNA code= Sagami 13). Ophiosabine densispina ( Mortensen, 1936) : PBBB / L84 , Burwood Bank , 54° 48.468´S, 59° 40.945´W to 54° 48.618´S, 59° 41.357´W, 694–727 m, 27/8/2018 GoogleMaps , CNP-INV ( DNA code= BB16-2 A). Ophiosabine pentactis ( Mortensen, 1936) : US AMLR-09/101-76, South Orkney Islands, 63° 1.09´S, 52° 21.94´W to 63° 1.07´S, 52° 26.74´W, 628– 627 m, 4/3/2009 GoogleMaps , MV F168830 ( DNA code=F168830). Ophiosabine rosea truncata ( Koehler, 1930) : TAN0308/85, Lord Howe plateau, 34° 13.89´S, 162° 40.59´E, 515–700 m, 26/5/2003 GoogleMaps , MV F99721 View Materials ( DNA code= F99721 View Materials ). Ophiosabine sp. MoV.5491 SS02/2007/77, Cascade 1200m 5, 43° 55.406´S, 150° 27.889´E to 43° 55.778´S, 150° 28.352´E, 590–660 m, 10/4/2007, MV F146270 ( DNA code= MVF146270 ). Ophiosabine vivipara (Ljungman, 1870) : ICEFISH/18-OT14, Falkland Islands, 52° 7.07´S, 58° 4.37´W to 52° 9´S, 58° 6.07´W, 82–104 m, 28/5/2004 GoogleMaps , MV F167535 ( DNA code=F167535) .

Diagnosis. Disc covered in dense multifid spinelets with a round pedicel, waisted stalk and>10 divergent apical thorns. Oral shields wider than long but with rounded distal margin, trapezoid adoral shields occur proximal to oral shields, 4–5 oral papillae. Arms 5, DAPs triangular separate, VAPs wider than long, separate, to 10 arm spines, uppermost to smooth to 4 segments in length, lower ones with a few basal thorns, one ovate tentacle scale, to ½ the segment in length.

Description. Holotype 7.5 mm dd, disc pentagonal, covered in dense multifid spinelets that obscure the underlying scales, radial shields to 1/4 dd, distal section naked (without spinelets), spinelets with a round pedicel, waisted stalk and>10 divergent apical thorns, spinelets reduced to a conical stump near oral shield. Bursal slit open, extending from oral shield to near disc margin. Oral shields wider than long, with an obtuse angle proximally, straight laterodistal edges and a rounded to truncate distal side. Adoral shields proximal to oral shield, 2x wider than long, trapezoid, with shorter distal edge, contiguous interradially with neighbouring adoral, and radially with first ventral arm plate. Jaw as wide as long, bearing 4–5 oral papillae along each side, inner papillae spiniform to narrowly lanceolate, distal ones more thickened mid-height with a constricted base and bluntly pointed apex, 2nd papillae often the largest. Teeth 2x as long as wide, with a rounded proximal edge, up to 8 in a vertical series, the dorsalmost one often narrower.

Arms five, 7x dd (55+ mm), broadly triangular in cross section, with a narrow rounded dorsal surface and flat widened ventral surface. DAPs 1/2 as wide as arm, triangular-shaped with straight to slightly convex distal edge, glassy, separate. LAPS widened under arm ridge (arms not moniliform), meet dorsally and ventrally after the 3rd arm segment. 1st VAP wider than long but much smaller than succeeding plates, succeeding VAPs 1.5x as wide as long, 1/2 width of the arm segment, with obtuse proximal sides, incised lateral edges (around pore), and convex distal edge, glass-like or transversely striated, just separated. Up to 10 arm spines, that almost meet dorsally on proximal segments, upper spine longest, to 4 segments ( 2.5 mm) long, smooth, hollow, bluntly pointed; middle ones 1/2 as long as upper spines, with a few thorns at their base; lowest spines narrow to sabre-shaped, to one segment ( 0.7 mm) long, distally developing a terminal proximal-orientated hook-like thorn. Tentacle scale single, elliptical to ovate, 1/2 as long as the ventral arm plate, becoming narrower distally. Colour (preserved): white with pale-grey disc, some brown shading on oral/adoral shields, oral papillae, and around the base of lower proximal arm spines.

Non type variations. Disc to 9 mm dd (NHMUK 2025.46), arms 6+ times dd. Radial shields can be prominent white lines on disc, naked for their entire extent. Some distal oral papillae have a longitudinal groove and/or a truncate tip (MV F321041). Oral shields can be depressed in the centre (NHMUK 2025.53) or almost as long as wide with a minor distal lobe.

Paratype ossicles MV F321041. Vertebrae zygospondylous with a long narrow zygosphene ( Fig. 17a View FIGURE 17 ). The external stereom of the LAP is dense proximally, with fine perforations orientated into vertical striations; distally (around the spine articulations) it is more open and regularly perforated ( Fig. 17f View FIGURE 17 ). Spine articulations ( Fig. 17g View FIGURE 17 ) are freestanding in a continuous vertical row on a raised distal portion of the LAP, ear-shaped, composed of a thicker dorsal and thinner ventral lobe, just merged proximally, enclosing a large round muscle opening and a smaller slit-like nerve opening. Disc plates irregular with flat perforated sections and peripheral thorny extensions ( Fig. 17h View FIGURE 17 ). Disc spinelets with a perforated pedicel, constricted shank and>=10 divergent apical thorns, 1/3 as long as the spinelet ( Fig. 17i View FIGURE 17 ). Oral plate almost as high as long, proximal and distal sections strongly fused together ( Fig. 17j View FIGURE 17 ). Radial shield hockey-stick shaped, with a distal lobe ( Fig. 17m View FIGURE 17 ).

Distribution. SW Indian Ridge ( 707–994 m).

Remarks. This species is reminiscent of the holotype of Ophiacantha parcita Koehler, 1906 found off Cape Verde Islands in the equatorial Atlantic Ocean at 633– 598 m depth. Both have dense spinelets with a smooth shank and multiple divergent thorns, adoral shields that are situated proximal to the oral shields, striated VAPs, blunt hollow arm spines, the lowermost slightly curved, and oval tentacle scales. But O. parcita differs in having shorter fewer thorns on disc spinelets, longer oral shields with a distinct distal lobe, thicker adoral shields, and only 3 oral papillae. O’Hara & Thuy (2022) included O. parcita and the similar O. notata ( Koehler, 1906) in their new genus Ophiosabine . We do not have DNA sequences of O. parcita or O. notata , however, genetic sequences of this new species are sister to the main Ophiosabine clade. Ophiosabine multifida and O. parcita have oral shields that are as wide or wider than long (especially proximally), whereas they are notably longer than wide in other species.

All three DNA samples of O. multifida are very similar, indicating the same species occurs on both Coral Seamount and Atlantis Bank on the SW Indian Ocean Ridge.

Etymology. Meaning multiply-divided (Latin, feminine), in reference to the numerous divergent thorns on the disc spines.