Review of Ophioplinthaca Verrill, 1899 (Echinodermata, Ophiuroidea, Ophiacanthidae), description of new species in Ophioplinthaca and Ophiophthalmus, and new records from the Northwest Pacific and the South China Sea Author Nethupul, Hasitha Institute of Deep-sea Science and Engineering, Chinese Academy of Sciences, CAS, 57200 Sanya, China & University of Chinese Academy of Sciences, Beijing 100039, China Author Stoehr, Sabine https://orcid.org/0000-0002-2586-7239 Swedish Museum of Natural History, Dept of Zoology, Box 50007, 10405 Stockholm, Sweden Author Zhang, Haibin https://orcid.org/0000-0001-5429-9851 Institute of Deep-sea Science and Engineering, Chinese Academy of Sciences, CAS, 57200 Sanya, China hzhang@idsse.ac.cn text ZooKeys 2022 2022-05-11 1099 155 202 http://dx.doi.org/10.3897/zookeys.1099.76479 journal article http://dx.doi.org/10.3897/zookeys.1099.76479 1313-2970-1099-155 A963E7C7F1BF4BF2BB4FA0CD5D319691 2D995654666955B2B228852B9EA78EAC Ophiophthalmus serratus sp. nov. Figs 15 , 16 Material examined. Holotype . China • 1 specimen ; South China Sea , Haima cold seep; 16°42.45'N , 110°25.68'E ; depth 1378 m ; 05 February 2021 ; Collecting event: stn. SC036; Shenhaiyongshi msv leg; preserved in 95% ethanol; GenBank: OK043837 ; IDSSE-EEB-SW0136 . Paratypes . China • 5 specimens ; South China Sea , Haima cold seep; 16°42.45'N , 110°25.68'E ; depth 1378 m ; 05 February 2021 ; Collecting event: stn. SC036; Shenhaiyongshi msv leg; preserved in 95% ethanol; GenBank: OK043838 ; IDSSE-EEB-SW0137 to IDSSE-EEB-SW0141. • 9 specimens ; South China Sea , Haima cold seep; 16°44.02'N , 110°27.61'E ; depth 1388 m ; 01 May 2018 ; Collecting event: stn. SC036; Shenhaiyongshi msv leg; preserved in 95% ethanol; IDSSE-EEB-SW0114 to IDSSE-EEB-SW0122. • 13 specimens ; South China Sea , Haima cold seep; 16°43.75'N , 110°28.34'E ; depth 1378 m ; 05 February 2021 ; Collecting event: stn. SC037; Shenhaiyongshi msv leg; preserved in 95% ethanol; IDSSE-EEB-SW0123 to IDSSE-EEB-SW0135. • 2 specimens ; South China Sea , Haima cold seep; 16°34.13'N , 110°42.55'E ; depth 1408 m ; 07 February 2021 ; Collecting event: stn. SC042; Shenhaiyongshi msv leg; preserved in 95% ethanol; IDSSE-EEB-SW0142, IDSSE-EEB-SW0143 . Diagnosis. Disc circular to sub-pentagonal, covered by dense smooth granules. Radial shields ovoid, naked, and widely separated (Fig. 15A ). One pointed ventralmost tooth and three slightly smaller, spiniform, finely rugose, pointed lateral oral papillae (Fig. 15E ). Dorsal arm plates triangular to fan-shaped, contiguous on proximal part of arm, then separated. Five finely serrated, arm spines with blunt tip, and one slightly elongated, blunt tipped tentacle scale (Fig. 15F-I ). Figure 15. Ophiophthalmus serratus sp. nov., holotype (IDSSE-EEB-SW0136) A dorsal disc B ventral disc C center of the disc D radial shield E oral frame dorsal side of the arm base G dorsal arm (proximal half) H dorsal arm (distal half) I ventral side of the arm base J ventral arm (proximal half) K ventral arm (distal half) L lateral arm base M lateral arm (proximal half) N lateral arm (distal half). Abbreviations: ars arm spine, as adoral shield, dap dorsal arm plate, das dorsal arm spine, gra granules, gs genital slit, j jaw, lap lateral arm plate, os oral shield, rs radial shield, ts tentacle scale, vap ventral arm plate, vas ventral arm spine. Scale bars: 2 mm ( A, B ); 1 mm ( D-F, J, L ); 500 µm ( C, G-I, K, M ); 200 µm ( N ). Holotype description. Disc diameter 9.5 mm, arm base width 1.65 mm, and arm length 45-50 mm (Fig. 15 ). Disc . Disc circular to sub-pentagonal, raised above arm base, and covered by overlapping irregular scales, bearing rounded to cylindrical stumps with blunt tip, and smooth granules (Fig. 15A-C ). Granules densely covering the surface, except radial shields, and small area in the center of the disc (Fig. 15C, D ). Radial shields, ovoid, small, slightly longer than wide, naked, and widely separated (Fig. 15D ). Distal edge of dorsal arm plate on arm base covered by row of few small granules, but only on two arms (Fig. 15F ). Ventral disc also covered by overlapping scales with granules, but fewer granules near oral shields (Fig. 15E ). Genital slits large, conspicuous, and extending from oral shield to periphery of disc (Fig. 15E ). Oral shield triangular, twice as wide as long (madreporite almost as long as wide), distal end with median lobe, proximal edges straight to slightly concave, and lateral angle connected to first lateral arm plate (Fig. 15E ). Adoral shields 3 x as long as wide, with straight lateral margins, and pair of shields barely connected proximally (Fig. 15E ). Adoral shields connected to first lateral and ventral arm plates (Fig. 15E ). Jaw large, as wide as long, with one pointed ventralmost tooth and three elongated, separated, pointed, finely rugose lateral oral papillae, slightly smaller than ventralmost tooth (Fig. 15E ). Arms . Dorsal arm plates triangular to fan-shaped, twice as wide as long, distal edge slightly convex, contiguous at proximal end of arm, then separated (Fig. 15F-H ). Ventral arm plate on first arm segment small, triangular, pointed distally, and slightly curved inwards proximally (Fig. 15I ). Second to third ventral arm plates slightly pentagonal, wider than long, straight proximal margins, and obtuse or wavy distal edge (Fig. 15I ). Following plates, as wide as long, straight lateral and proximal margins, and straight to wavy distal edge (Fig. 15J ). Ventral arm plates separated along arm, including first plate (Fig. 15I-K ). Lateral arm plates meeting below and above, except on dorsal arm base (Fig. 15G-N ). Five finely serrated arm spines, with blunt tip in proximal to middle regions of arm, then reduced to four at distal half of arm (Fig. 15H, K, N ). Dorsal arm spines one and a half to two arm segments in length (Fig. 15F, L, M ). Ventral arm spines shorter, one or one and a half arm segments in length (Fig. 15J, L, M ). Dorsalmost arm spine longest, next two arm spines slightly shorter, but both similar in length, and last two ventral arm spines shortest, also equal in length (Fig. 15L, M ). Arm spines increasingly finely serrated to thorny, and shorter at distal end of arm (Fig. 15K, N ). One slightly elongated, blunt tipped tentacle scale, nearly as long as ventral arm plate (Fig. 15I, J ). Color . In ethanol, whole specimen pale brown-white. (Fig. 15 ). Ossicle morphology of paratype. IDSSE-EEB-SW0137: Arm spine articulations well developed, five in number, and placed at slight angle to distal edge of lateral arm plate. Volute-shaped perforated lobe forms dorsal and distal part of articulation, but turns into two unequal subparallel curved lobes ventralwards; large muscle opening and small nerve opening (Fig. 16A ). Proximal half of inner side of lateral arm plate with depression (Fig. 16B ). Arm spines thorny, finely serrated with blunt apex (Fig. 16C, D ). Vertebrae with streptospondylous articulation, short, broad podial basin at proximal end (Fig. 16E-J ). Dorsal side of vertebrae distally triangular and proximally flattened with shallow longitudinal groove along midline (Fig. 16E-G ). Ventral end of vertebrae with broad ambulacral groove with pair of lateral ambulacral canals, oral bridge absent (Fig. 16H-J ). Figure 16. Ophiophthalmus serratus sp. nov., paratype (IDSSE-EEB-SW0137) A, B lateral arm plate C dorsal arm spine D ventral arm spine E-J vertebrae E-F proximal view G distal view H ventral view I dorsal view J lateral view. Abbreviations: d dorsal, de depression, dist distal, dl dorsal lobe, lac lateral ambulacral canals, mo muscle opening, no nerve opening, pb podial basin, prox proximal, v ventral, vl ventral lobe. Scale bars: 500 µm ( A-C, E-J ); 300 µm ( D ). Paratype variations. Here, we examined 29 paratypes, ranging in disc diameter from 4 mm to 17 mm, and found only few notable variations among them. Large specimens had five arm spines at proximal to middle regions of the arm, then reduced to four arm spines at distal end, but small specimens showed five arm spines only at arm base, then reduced to four along the distal half of the arm. However, the finely serrated surface of the arm spine was similar in both small and large specimens. The number of lateral oral papillae differed from three to four, but most specimens had three papillae. Most specimens had dense granular coverage of the disc except larger specimens (16-17 mm). Color ranges from creamy white to dark among specimens from our collection. The above mentioned variations depend mainly on the size of the disc, and specimens with similar disc diameter showed similar morphological characters. Distribution. 1378-1408 m in depth, Haima cold seep, South China Sea. Etymology. The species name was derived from the Latin word serratus (saw like, serrate), alluding to the surface of the arm spine. Remarks. All specimens of Ophiophthalmus serratus sp. nov. were collected from a methane cold seep in the South China Sea. Ophiophthalmus serratus sp. nov. showed similar morphological characters to three congeners, except O. hylacanthus . Ophiophthalmus normani resembles O. serratus sp. nov. in having similar radial shield and arm plate characters, and granule coverage on the disc, but differs in number of arm spines (up to four), peg-like lateral oral papillae, smooth and slender arm spines, spaced granular coverage, arrangement of arm spines at lateral arm plate, and large oval tentacle scales ( Lyman 1879 ; H. L. Clark 1911 ; Koehler 1922 ; Liao 2004 ). Ophiophthalmus cataleimmoidus is similar to O. serratus sp. nov. by having similar radial shield and arm plate characters, and granular coverage on the disc, but differs in number of arm spines (up to six or seven), smooth arm spines, and shape of the tentacle scales (H. L. Clark 1911 ; Liao 2004 ). Ophiophthalmus relictus is similar to O. serratus sp. nov. by having similar radial shield and arm plate characters, and granular coverage on the disc, but differs in pointed to conical granules, six rough, short, and stout arm spines, and pointed tentacle scales ( Koehler 1904 ; H. L. Clark 1911 ). Ophiophthalmus hylacanthus is similar to O. serratus sp. nov. by having similar radial shield and oral frame characters, but differs significantly by rough spines on the disc, up to eight arm spines, short genital slits, and narrow, pointed tentacle scales (H. L. Clark, 1911).