Ophiambix kagutsuchi, Okanishi & Kato & Watanabe & Chen & Fujita, 2020

Okanishi, Masanori, Kato, Moe, Watanabe, Hiromi Kayama, Chen, Chong & Fujita, Toshihiko, 2020, Large populations of two new species of Ophiambix (Echinodermata, Ophiuroidea) discovered on Japanese hot vents and cold seeps, Raffles Bulletin of Zoology 68, pp. 196-213 : 198-202

Ophiambix kagutsuchi , new species

(New Japanese name: Kagutsuchi-kaede-kumohitode) ( Figs. 2–5 )

Holotype. R / V YOKOSUKA, DSV SHINKAI 6500 : NSMT E-13071, ethanol, collected with slurp gun, cruise YK17-17, Dive #1508, hydrothermal vent at Tarama Knoll ( Yamanaka et al., 2015), Okinawa Trough, off Sakishima Island, Okinawa Prefecture, southwest of Japan, 25°05.4573′N, 124°32.7256′E, 1,730 m, 3 August 2017.

Paratypes. NSMT E-13072 (40 specimens, ethanol) , NSMT E-13073 (2 specimens, ethanol), collected in the same locality as the holotype . NSMT E-13070 (1 specimen, ethanol), and NSMT E-13069 (7 specimens, ethanol), collected with slurp gun, cruise YK17-17, Dive #1509, hydrothermal vent at Tarama Knoll, Okinawa Trough, off Sakishima Island , Okinawa Prefecture, southwest of Japan, 25°05.4734′N, 124°32.6917′E, 1,979 m, 4 August 2017 .

R / V NATSUSHIMA, ROV HYPER DOLPHIN: NSMT E-13036 (2 specimens, ethanol), collected with slurp gun, cruise NT11-20, Dive #1331, Hatoma Knoll field, Okinawa Trough , Sakishima Islands, Okinawa Prefecture, southwest of Japan, 24°51.477′N, 123°50.507′E, 1,477 m, 9 October 2011 . NSMT E-13037 (1 specimen, ethanol), collected with slurp gun, cruise NT11-20, Dive #1329, Izena Hole field, off Okinawa Island, Okinawa Prefecture, southwest of Japan, 27°14.815′N, 127°04.089′E, 1,617 m, 5 October 2011 . NSMT E-13038 (5 specimens, ethanol) and NSMT E-13039 (5 specimens, ethanol), collected with slurp gun, cruise NT10-07, Dive #1118, sunken wood at Ryukyu Trench, Sakishima Islands , Okinawa Prefecture, southwest of Japan, 24°57.186′N, 125°57.294′E, 276 m, 27 April 2010 . NSMT E-13040 (3 specimens, ethanol), collected with slurp gun, cruise NT10-07, Dive #1114, sunken wood at Ryukyu Trench, Sakishima Islands , Okinawa Prefecture, southwest of Japan, 24°45.000′N, 126°44.982′E, 499 m, 22 April 2010 . NSMT E-13041 (15 specimens, ethanol) and NSMT E-13042 (3 specimens, ethanol), collected with slurp gun, cruise NT09-10, Dive #1031, sunken wood at Ryukyu Trench, Sakishima Islands , Okinawa Prefecture, southwest of Japan, 24°57.186′N, 125°57.294′E, 276 m, 12 July 2009 .

R / V NATSUSHIMA, DSV SHINKAI 2000 : NSMT E-13043 (1 specimen, ethanol), collected with slurp gun, cruise NT02- 07, Dive #1359, Hatoma Knoll field, Okinawa Trough , Sakishima Islands, Okinawa Prefecture, southwest of Japan, 24°51.596′N, 123°50.376′E, 1,469 m, 6 June 2002 . NSMT E-13044 (6 specimens, ethanol), cruise NT02-07, Dive #1354, Hatoma Knoll field, Okinawa Trough, Sakishima Islands , Sakishima Islands, Okinawa Prefecture, southwest of Japan, 24°51.468′N, 123°50.497′E, 1,473 m, 29 May 2002 . NSMT E-13045 (13 specimens, ethanol), collected with slurp gun, cruise NT01-05, Dive #1277, Hatoma Knoll field, Okinawa Trough , Sakishima Islands, Okinawa Prefecture, southwest of Japan, 24°51.649′N, 122°50.292′E, 1,497 m, 29 May 2001 . NSMT E-13046 (3 specimens, ethanol), collected with manipulator, cruise NT01-05, Dive #1276, Dai-yon Yonaguni Knoll field, Okinawa Trough , Sakishima Islands, Okinawa Prefecture, southwest of Japan, 24°50.790′N, 122°42.090′E, 1,384 m, 28 May 2001 . NSMT E-13047 (1 specimen, ethanol), collected with manipulator, cruise NT01- 05, Dive #1276, Dai-yon Yonaguni Knoll field, Okinawa Trough , Sakishima Islands, Okinawa Prefecture, southwest of Japan, 24°50.666′N, 122°42.047′E, 1,386 m, 28 May 2001 . NSMT E-13048 (1 specimen, ethanol), NT00-06, cruise Dive #1189, Hatoma Knoll field, Okinawa Trough, Sakishima Islands , Okinawa Prefecture, southwest of Japan, 24°51.402′N, 123°50.646′E, 1,468 m, 29 May 2000 . NSMT E-13049 (1 specimen, ethanol), cruise NT00-06, Dive #1184, Hatoma Knoll field, Okinawa Trough, Sakishima Islands , Okinawa Prefecture, southwest of Japan, 24°51.229′N, 123°50.458′E, 1,523 m, 21 May 2000 . NSMT E-13050 (1 specimen, ethanol), collected with slurp gun, cruise NT99- 07, Dive #1094, Iheya North Original Site , Iheya North field, Okinawa Trough, Okinawa Prefecture, southwest of Japan, 27°47.022′N, 126°54.000′E, 1,000 m, 8 May 1999 . NSMT E-13051 (2 specimens, ethanol) , NSMT E-13052 (1 specimen, ethanol), collected with slurp gun, cruise NT99-07, Dive #1094, Iheya North Original Site , Iheya North field, Okinawa Trough, Okinawa Prefecture, southwest of Japan, 27°47.262′N, 126°53.921′E, 990 m, 8 May 1999 . NSMT E-13053 (2 specimens, ethanol), collected with manipulator, cruise NT99-07, Dive #1093, Iheya North Original Site , Iheya North field, Okinawa Trough, Okinawa Prefecture, southwest of Japan, 27°47.190′N, 126°54.133′E, 1,058 m, 7 May 1999 . NSMT E-13054 (6 specimens, ethanol), cruise NT99-07, Dive #1092, Iheya North Original Site , Iheya North field, Okinawa Trough, Okinawa Prefecture, southwest of Japan, 27°47.220′N, 126°53.913′E, 968 m, 6 May 1999 . NSMT E-13055 (46 specimens, ethanol), cruise N96-07, Dive No. #0863, Iheya North Original Site , Iheya North field, Okinawa Trough, Okinawa Prefecture, southwest of Japan, 27°47.178′N, 126°54.149′E, 1,049 m, 7 May 1996 .

R / V NATSUSHIMA, ROV DOLPHIN 3 K: NSMT E-13056 (6 specimens, ethanol), cruise NT98-08, Dive #0376, Iheya North Original Site , Iheya North field, Okinawa Trough, Okinawa Prefecture, southwest of Japan, 27°47.502′N, 126°54.000′E, 21 June 1998 .

Diagnosis. Aboral disc as well as arms covered by small granules separated from each other. Second from oral-most arm spines on proximal portion of arm flattened and long. Teeth flattened and forming a horizontal row on oral-most edge of dental plate. Tentacle scales on each tentacle pore two in number, spiniform (width/length: 1/3–1/4), smaller than tentacle pore on proximal portion of the arm ( Table 1).

Etymology. The species epithet “kagutsuchi” is named for Kagutsuchi, the Japanese god of fire in an ancient Japanese mythology, referring to the hot-vent habit of the new species. Noun held in apposition.

Description of holotype (NSMT E-13071). Disc. Pentagonal, 4 mm in diameter ( Fig. 2A ). Aboral surface covered by small granules of almost uniform size, separated from each other, approximately 50–70 μm in diameter ( Fig. 2B ). Removal of granules shows underlying plates are scalar, circular in outline, and imbricating, each approximately 250–350 μm in diameter ( Fig. 2B ). Radial shields triangular, distally wider, 350 μm in width, 350 μm in length and sharpen to centre ( Fig. 2B ), and completely concealed by the granules ( Fig. 2B ). On oral surface, adoral shields parallelogram-shaped, wider than long, approximately 250 μm in width, 120 μm in length ( Fig. 2C ), one overlapping the other. Oral plates trapezoidal, approximately 250 μm in width, 180 μm in length at radial edge, 250 μm in length at abradial edge, in contact with each other ( Fig. 2C ). Oral shields pentagonal, slightly rounded, with convex distal edge, approximately 360 μm in width, 60–260 μm in length ( Fig. 2C ). Interradial oral disc area narrow, covered by scales under thick skin, approximately 200–300 μm in length ( Fig. 2C ). Genital slits narrow, almost extending from edge of oral shield to two-thirds height of oral interradial disc, 0.1 mm width ( Fig. 2C ). Oral papillae and teeth rudimentary, very thin, narrow and flat ossicles, approximately 10 μm in length, forming a continuous horizontal row on oral edge of dental and oral plates ( Fig. 2C ). Teeth and oral papillae quite similar in shape but in this study and for descriptive purposes, the ossicles on top of the dental plate are called teeth and ossicles on oral edge of oral plate are called oral papillae. With the exception of the oral-most row of papillae, 6 to 7 thin and fan-shaped teeth forming vertical row on the dental plate. Second tentacle pore inside the mouth slit.

Arms. Five, one complete arm 5 mm long and other four arms have lost tips ( Fig. 2A ). 1.0 mm width and 0.5 mm height in proximal portion, elliptical in section. Arms tapering gradually toward the arm tip ( Fig. 2A ).

On proximally arm, aboral surface covered by small granules as those on aboral disc ( Fig. 2D ) decreasing in number and disappearing on arm tip ( Fig. 2F ). After removal of the granules, exposed dorsal arm plates oblong, longer than wide, proximal edge slightly wider than distal edge ( Fig. 2D ). A pair of fan-shaped supplementary dorsal arm plates on both lateral sides of each dorsal arm plate ( Fig. 2D ) and irregularly shaped smaller supplementary plates on distal side of dorsal arm plates separating them from each other ( Fig. 2D ). On middle portion of the arm, these supplementary plates disappear and dorsal arm plates are in contact, gradually decreasing in size toward the arm tip ( Fig. 2F ). Lateral arm plates thin, widely separated from each other throughout the arm ( Fig. 2C, E, G ). Tentacle pore forming large hole ( Fig. 2C, E, G ). On proximal portion of the arm, ventral arm plates almost square with concave distal edge ( Fig. 2C, E ) and toward the arm tip, becoming oblong, longer than wide with distal concave edge ( Fig. 2G ), contiguous throughout the arms ( Fig. 2G ). Three flat and pointed arm spines on proximal portion of arms, middle one longest, same length as corresponding arm segment, aboral-most half length of the middle spine, and the oral-most spine shortest, approximately one-fifth length of the middle spine ( Fig. 2D ). Arm spines decreasing in number to one toward arm tip, transforming into hook-shape, approximately the same length as the corresponding arm segment ( Fig. 2F, G ) (see detailed descriptions of each ossicle in next section). One small, rudimentary tentacle scale at each tentacle pore ( Fig. 2E ) although small, tentacle scales present on distal portion of arm ( Fig. 2G ).

Description of ossicle morphology (paratypes, NSMT E-13070 and NSMT E-13050). Vertebrae streptospondylouslike articulation with zagapophyses framing the water vascular canal on proximal side (Fig. 3B); large wing-like muscle flanges on oral-distal side (Fig. 3A, C); longitudinal groove on oral side (Fig. 3C); a pair of lateral ambulacral canals opening inside the oral groove (Fig. 3C); “T”-shaped groove on aboral side (Fig. 3D); narrow and thick, long “lateral shield” covering lateral-oral side (Fig. 3B, C), forming a large depression on oral fossae on proximal side (Fig. 3B).

Lateral arm plates longer than high, oblong (Fig. 3G) with thin leaf-like projection to inner side (Fig. 3E–G). On inner side, one well-defined elevated structure, consisting of open meshed stereom, on aboral-proximal side (Fig. 3G). A single perforation opening on aboral-distal side (Fig. 3G). On external side, three spine articulations on oral-distal edge (Fig. 3E–G), composed of horizontal dorsal and ventral lobes, basically parallel but opening toward external side (Fig. 3E). Middle articulation the largest, aboral and oral ones slightly smaller than middle one (Fig. 3E). Ventral lobes slightly larger than dorsal lobes (Fig. 3E, F). Nerve and muscle openings between the lobes, separated by a bridge (Fig. 3E). Ventral arm plates basically oblong, longer than wide, concave on both lateral sides and distal side (Fig. 3H).

Arm spines flattened and pointed on proximal to middle portion of arms and on distal portion of the arm, transforming into hook with up to four secondary teeth (Fig. 3I, J).

Oral plates irregularly oblong, with notches for water ring canals and oral tentacles on aboral periphery part and oral central part, respectively ( Fig. 4A, B ). Depression for aboral tentacle located just below the notch for water ring canal ( Fig. 4B ). Abradial and adradial muscular attached area on middle portion of abradial side ( Fig. 4A ) and aboral central portion ( Fig. 4B ) of adradial side, respectively. A presumable depression for water ring canal on aboral central part of abradial side ( Fig. 4A ). Adradial genital plate “T”-shaped, distally wider, the length approximately two times longer than width ( Fig. 4C, D ). No distinctive articulation for radial shield ( Fig. 4C, D ). Radial shield triangular with round apexes, slightly pointing to centre part of the disc, with two slight depressions, indicating articulations for adradial genital plates at periphery of disc on inner side ( Fig. 4E ). Dental plate pyramid-shaped, facing its flat aspect to oral surface ( Fig. 4F ). No distinctive articulation for teeth recognisable for the dental plate ( Fig. 4F ).

Colour. Uniformly creamy white in alcohol. Living colour is unknown.

Distribution. Japan: hydrothermal vents in Okinawa Trough and sunken wood found in Ryukyu Trench, southwest of Japan. Depth range 276–1,979 m ( Fig. 1 ).

Remarks. Ophiambix kagutsuchi , new species, can be distinguished from the other four congeners and Ophiambix macrodonta , new species, by: 1) armament of aboral body; 2) shape and arrangement of teeth; 3) shape of arm spine; 4) aboral disc covered by small granules arranged in circles surrounding the periphery of the disc scales, and absence of granules on the aboral arm surface; 5) teeth are flat, minute, forming a horizontal row on the oral-most edge of the dental plate; 6) second oral-most arm spines are flat and leaf-like; 7) number, size, and shape of tentacle scales (see also Table 1 and Remarks of O. macrodonta , new species, below).

The 175 examined specimens showed various developmental stages (0.8 to 3.2 mm in disc diameter), probably from juvenile to adult, but the diagnostic characters could be observed for all specimens.

Figures

Fig. 2. Ophiambix kagutsuchi, new species, holotype (NSMT E-13071). A, aboral body; B, aboral disc and proximal portion of arm; C, oral disc and proximal portion of arms, arrow heads indicate oral papillae; D, proximal portion of aboral surface of arm; E, proximal portion of oral surface of arm; F, distal portion of aboral surface of arm; G, distal portion of oral surface of arm. Abbreviations: ASh, adoral shield; ASp, arm spine; D, dorsal arm plate; GS, genital slit; L, lateral arm plate; OP, oral plate; OS, oral shield; RS, radial shield; SD, supplementary dorsal plate; Te, tentacle scale; V, ventral arm plate. Scale bars = 1 mm.

Fig. 4. Ophiambix kagutsuchi, new species, a paratype (NSMT E-13050), SEM images of ossicles. A, B, oral plates of abradial side (A) and adradial side (B), partly cracking, arrows indicate neural grooves; C, D, adradial genital plates, aboral view (C) and oral view, partly cracking (D); E, inner view of a radial shield; F, external view of a dental plate. Orientations: ab, aboral side; cen, centre of disc; o, oral side; per, periphery of disc. Abbreviations: AbMA, abradial muscle attachment area; AdMA, adradial muscle attachment area; AG, articulation for genital plate; DAT, depression for aboral tentacle; DOT, depression for oral tentacle; DW, presumable depression for water ring canal. Scale bars = 100 μm.

Fig. 5. Ophiambix macrodonta, new species, holotype (NSMT E-13059). A, aboral body; B, oral body; C, aboral disc and proximal portion of arm; D, aboral periphery of disc and proximal portion of arm; E, oral disc and proximal portion of arms; F, oral periphery of disc and proximal portion of arm; G, a jaw; H, top of a jaw, arrow heads indicate teeth and oral papillae. Abbreviations: ASh, adoral shield; DP, dental plate; GS, genital slit; L, lateral arm plate; OP, oral plate; OS, oral shield; RS, radial shield; Te, tentacle scale; V, ventral arm plate. Scale bars = 1 mm.

Fig. 1. A, known distribution of Ophiambix aculeatus, O. devaneyi, O. epicopus, O. kagutsuchi, new species, O. macrodonta, new species, and O. meteoris; B, enlarged area, sampling localities of examined specimens of Ophiambix aculeatus, O. epicopus, O. kagutsuchi, new species, and O. macrodonta, new species, in this study.