Ophiactis cf. brachygenys H. L. Clark, 1911

Nethupul, Hasitha, Stöhr, Sabine & Zhang, Haibin, 2022, New species, redescriptions and new records of deep-sea brittle stars (Echinodermata: Ophiuroidea) from the South China Sea, an integrated morphological and molecular approach, European Journal of Taxonomy 810 (1), pp. 1-95 : 68-81

Ophiactis cf. brachygenys H. L. Clark, 1911

Figs 40–42

Ophiactis brachygenys H.L. Clark, 1911: 135–137 , fig. 51. Ophiactis definita Koehler, 1922a: 187–189 , pl. 64 figs 1–2, 7.

Ophiactis definita – Koehler 1930: 121. — Guille 1981: 439.

Ophiactis brachygenys – Irimura 1991: 80. — Liao 2004: 228–229, fig. 134.

Material examined

CHINA • 1 spec.; South China Sea , SE of Zhongsha Islands, seamount; 13°58.65′ N, 114°52.09′ E; depth 1550 m; 25 Sep. 2020; collection event: stn SC013; MSV Shenhaiyongshi leg.; preserved in 95% ethanol; GenBank: MZ 198769 ; IDSSE EEB-SW0015 • 1 spec.; same collection data as for preceding; GenBank: MZ 198770 ; IDSSE EEB-SW0016 .

Description (IDSSE EEB-SW0015)

MEASUREMENTS. Disc diameter 5.8 mm, heptamerous specimen.

DiSC. Robust and sub-pentagonal, heptamerous ( Fig. 40A–B ). Dorsal disc covered by large, coarse, irregular, polygonal overlapping scales, denser in disc center ( Fig. 40A ). Radial shields large, broad, internal margin straight, external margin convex, pointed proximal angle, longer than wide, half disc radius long, completely separated by a single series of two or three plates ( Fig. 40D ). Ventral disc also covered by small, irregular, overlapping scales. Genital slits conspicuous and extending from oral shield to disc periphery ( Fig. 40C ). Oral shield spearhead-shaped, with wide proximal angle, wider than long ( Fig. 40F ). Adoral shield larger than oral shield, pair proximally connected, proximal edge concave, three times as long as than wide, slightly narrowing distally, bordering proximal edges of oral shield, not separating oral shield from arm ( Fig. 40F ). One large, wide, rectangular ventralmost tooth with tricuspid edge. Single large, broad (wider than teeth), axe-shaped, operculiform lateral oral papilla, covering second tentacle pore inside mouth angle ( Fig. 40F ). Some oral papillae more pointed laterally or tricuspid ( Fig. 40B, F ).

ARMS. Dorsal arm plate slightly fan-shaped, large, slightly convex distally, wide proximal angle, as long as wide and mostly separated ( Fig. 40G ). First ventral arm plate small, triangular with truncated distal end. Second ventral arm plate tetragonal or pentagonal, wider than long, connected to first ventral arm plate, then pentagonal with straight to concave distal edge, round proximal angle along arm and mostly separated ( Fig. 40B, H ). Three arm spines on most segments, with thickened base, rounded, blunt tip, 1–1½ arm segment in length, middle one longest ( Fig. 40G–H ). One large, broad, oval tentacle scale, half as long as ventral arm plate, covering pore completely ( Fig. 40H ).

COLOR. Wet specimen light brown, dry disc light grey and dorsal arm light brown or pink ( Fig. 40 ).

OSSiCLE MORPHOLOGY.Extracted from heptamerous specimen, lateral arm plate with three well-developed spine articulations formed by two subparallel, bent, separated lobes, unequal in size. Two similarly sized openings for muscle and nerve ( Fig. 41A–C ). Vertebrae with well-developed zygospondylous articulation, narrow, shallow dorsal furrow, not extending beyond distal articulating structures, deep ambulacral groove, widened distally, large podial basins ( Fig. 41D–H ).

Remarks

According to our specimens, Ophiactis cf. brachygenys is a fissiparous species and these are the first records of specimens with more than five arms (confirmed by molecular data, see below). Six- and seven-armed specimens had similar morphological features. However, the hexamerous specimen (2.8 mm disc diameter) differs slightly from the heptamerous specimen in the number of arms, the widely separated radial shield, the first one to two arm segments having four arm spines but only on one or two arms, and a smooth, pointed disc spine near the periphery of the disc ( Fig. 42 ).

The holotype description of O. brachygenys is similar to both specimens from the present study, except for the number of arms and completely separated radial shields.

H.L. Clark (1911) mentioned that one of his specimens (9 mm disc diameter) had distally separated radial shields, the dorsal arm plate was shorter and wider, and both dorsal and ventral arm plates were more closely together. Also, it had a few short disc spines at the periphery of the ventral disc (H.L. Clark 1911). These variations concur with the specimens from the present study ( Figs 40–42 ). Ophiactis definita was synonymized with O. brachygenys by Liao (2004). The description of O. definita is similar to that of O. brachygenys , but Koehler (1922a) described some morphological differences between the two species. Ophiactis brachygenys from the present study and the description of its holotype (H.L. Clark 1911) are morphologically distinguished from the type of O. definita by having separated dorsal arm plates along the arm, wider than long and not as broad radial shields, and wide as long oral shields. In addition, the radial shields are proximally and distally separated, and disc spines are present on the ventral disc ( Figs 40A , 42K, M ). Molecular analysis of both species from different localities suggests that these morphological variations may be species specific (see below).

Distribution

216–1550 m depth. Recorded from the Lubang Islands near the Philippines, East China Sea, southeast Japan, Indonesian seas, Coral Sea, Solomon Sea, Bismarck Sea and Timor Sea ( OBIS 2021).

Molecular phylogenetic analysis

Family Asteronychidae

Final 581 bp partial COI and 443 bp partial 16S sequences were obtained after removing ambiguous aligned sites and successfully used in reconstructing a Maximum Likelihood (ML) tree from 16S

(8 specimens) and COI (7 specimens), respectively ( Fig. 43 ). In the 16S ML tree, species of Asteronyx were divided into two subclades (Sub-Clades 01 and 02). Sub-Clade 01 consists of A. loveni ( Japan, East China Sea and South China Sea) and A. longifissus Döderlein, 1927 (California) . Sub-Clade 02 consists of A. reticulata (East China Sea and Japan) and A. luzonicus (South China Sea) ( Fig. 43A ). Similar results were found in the COI ML tree ( Fig. 43B ). Genetic distance values are provided in Suppl. file 1 and Suppl. file 2. Two samples of A. reticulata from Japan and the East China Sea had identical sequences and three samples of A. loveni from Japan, the East China Sea and the South China Sea also showed no sequence variation (Suppl. file 1).

Families Euryalidae and Gorgonocephalidae

A total of 26 COI sequences trimmed to 608 bp were obtained after removing ambiguous aligned sites and successfully used in reconstructing an ML tree ( Fig. 44 ). Two main clades were detected, with the family Euryalidae belonging to Clade 01 and family Gorgonocephalidae belonging to Clade 02. The genus Asteroschema was detected as a sub-clade within family Euryalidae (Sub-Clade 01) and the genus Gorgonocephalus was detected as a sub-clade within family Gorgonocephalidae (Sub-Clade 02). Two inter-clades were detected among species of Asteroschema (Sub-Clade 01). Inter-Clade 1A consisted of A. bidwillae and A. tubiferum from New Zealand (depth 1126–1444 m). Inter-Clade 1B consisted of A. edmondsoni A.H. Clark, 1949 from New Caledonia and A. horridum from the South China Sea and Reunion Island (depth 498–1550 m). Two inter-clades were detected among species of Gorgonocephalus (Sub-Clade 02). Inter-Clade 2A consists of Astrodendrum sagaminum ( Döderlein, 1902) from Japan, Gorgonocephalus pustulatum (H. L. Clark, 1916) from New Zealand, G. sundanus Döderlein, 1927 from Australia and G. cf. dolichodactylus from the South China Sea (depth 400–1114 m). Inter-Clade 2B consists of G. arcticus Leach, 1819 from Cornwallis Island, G. eucnemis ( Müller & Troschel, 1842) from Japan, G. chilensis from the Antarctic, the Southern Ocean, New Zealand and the South China Sea (depth 398–1550 m) ( Fig. 44 ). Genetic distance values are provided in Suppl. file 3 and Suppl. file 4.

Family Ophiomusaidae

A 568 bp sequence of the COI gene was obtained after removing ambiguous aligned sites and successfully used in reconstructing the ML tree for 13 specimens from the family Ophiomusaidae ( Fig. 45 ). Two main clades were detected within the family. Sub-Clade 01 represnts Ophiomusa scalare ( Lyman, 1878) , O. aspera ( Koehler, 1930) , O. simplex ( Lyman, 1878) and O. australe (H.L. Clark, 1928) . Sub-Clade 02 represents O. lymani , Ophiomusa sp. , O. miranda ( Koehler, 1930) , O. lunare ( Lyman, 1878) and O. anisacantha (H.L. Clark, 1928) ( Fig. 45 ). Genetic distance values are provided in Suppl. file 5.

Family Ophiotomidae

A 623 bp sequence of the COI gene was obtained after removing ambiguous aligned sites and used to reconstruct the ML tree from ten specimens for the family Ophiotomidae ( Fig. 46 ). We failed to get COI or 16S gene sequences from Ophiotreta eximia . Therefore, only Ophiopristis shenhaiyongshii sp. nov. was added to this phylogenetic tree from our collection. Two main clades were detected within Ophiotomidae . Inter-Clade 2A represents Ophiotreta matura , O. eximia , Ophiopristis shenhaiyongshii sp. nov., O. luctosa , O. procera and Ophiacantha spectabilis G.O. Sars, 1872 ( Fig. 46 ). Genetic distance values are provided in Suppl. file 6.

Family Ophiacanthidae

Final 449 bp COI and 487 bp 16S sequences were obtained after removing ambiguous aligned sites and successfully used in reconstructing Maximum Likelihood (ML) trees of 16S (8 specimens) and COI (7 specimens), respectively ( Fig. 47 ). In the 16S ML tree, species from the South China Sea divided into two subclades (Sub-Clades 01 and 02). Ophiurothamnus clausa , Ophiomoeris petalis sp. nov., Ophiomoeris sp. , Ophiacantha aster sp. nov. and Ophioplinthaca plicata from the present study fell into Sub-Clade 01. Ophiacantha vorax , O. bathybia and Ophientrema scolopendrica from the present study fell into Sub-Clade 02. The genus Ophioplinthaca fell into a new interclade within Sub-Clade 01 (Inter-Clade 1B). Inter-Clade 1A consists of three different genera: Ophiacantha , Ophiomoeris and Ophiurothamnus . Ophientrema scolopendrica , Ophiacantha bathybia and O. vorax also fell into two interclades within Sub-Clade 02 (Inter-Clades 2A and 2B) ( Fig. 47A ).

The clades in the COI ML tree were grouped corresponding to the 16S ML tree. Therefore, all the species represented in the COI ML belong to the main Clade 02. Ophiurothamnus clausa and Ophioplinthaca plicata from the South China Sea fell into Sub-Clade 01. Ophiacantha vorax and Ophientrema scolopendrica from the South China Sea fell into Sub-Clade 02. The genus Ophioplinthaca fell into Inter-Clade 1B within Sub-Clade 01 ( Fig. 47B ). The topology of the two ML trees was slightly different from each other (Sub-Clade 01). Genetic distance values are provided in Suppl. file 7 and Suppl. file 8.

Family Ophiactidae

A total of 18 COI sequences trimmed to 554 bp were obtained after removing ambiguous aligned sites and were used to reconstruct the ML tree ( Fig. 48 ). Two main clades were detected within the family. Sub- Clade 02 represented all Ophiactis species recorded from the South China Sea. Ophiactis cf. perplexa ,

O. cf. brachygenys and O. profundi fell into two inter-clades within Sub-Clade 02 (Inter-Clades 2A and 2B) ( Fig. 48 ). Genetic distance values are provided in Suppl. file 9.

Figures

Fig. 40. Ophiactis cf. brachygenys H.L. Clark, 1911 (IDSSE EEB-SW0015 = heptamerous specimen). A. Dorsal disc. B. Ventral disc (first and second ventral arm plates highlighted). C. Lateral disc. D. Radial shields. E–F. Oral frame (operculiform lateral oral papillae highlighted). G. Dorsal arm. H. Ventral arm. Abbreviations: as = adoral shield; dap = dorsal arm plate; gs = genital slit; os = oral shield; rs = radial shield; tp = tentacle pore; ts = tentacle scale; vap = ventral arm plate. Scale bars: A–B = 1 mm; C–E, G–H = 500 µm; F = 200 µm.

Fig. 41. Ophiactis cf. brachygenys H.L. Clark, 1911, SEM (IDSSE EEB-SW0015 = heptamerous specimen). A–C. Lateral arm plate (internal, external). D–H. Vertebrae. D. Proximal view. E. Distal view. F. Ventral view. G. Dorsal view. H. Lateral view. Abbreviations: D = dorsal; Dist = distal; dl = dorsal lobe; mo = muscle opening; no = nerve opening; Prox = proximal; V = ventral; vl = ventral lobe. Scale bars = 300 µm.

Fig. 42. Ophiactis cf. brachygenys H.L. Clark, 1911 (IDSSE EEB-SW0016 = hexamerous specimen). A. Dorsal disc. B. Ventral disc. C. Radial shields. D. Lateral disc. E. Disc spine. F. Oral frame. G. Dorsal arm. H. Ventral arm. Abbreviations: as = adoral shield; dap = dorsal arm plate; ds = disc spine; gs = genital slit; os = oral shield; rs = radial shield; tp = tentacle pore; ts = tentacle scale; vap = ventral arm plate. Scale bars: A–B = 500 µm; C–H = 200 µm.

Fig. 43. Family Asteronychidae Ljungman, 1867, Maximum likelihood (ML) trees based on partial 16S and COI sequences (bootstrap support values were generated with rapid bootstrapping algorithm for 1000 replicates). A. 16S ML. B. COI ML. Abbreviations: ECS = East China Sea; JP = Japan; SC = Sub-Clade; SCS = South China Sea.

Fig. 44. Families Euryalidae Gray, 1840 and Gorgonocephalidae Ljungman, 1867, Maximum likelihood (ML) tree based on partial COI sequences (bootstrap support values were generated with rapid bootstrapping algorithm for 1000 replicates). Abbreviations: AN = Antarctica; IC = Inter-Clade; NZ = New Zealand; RI = Reunion Island; SC = Sub-Clade; SCS = South China Sea; SO = Sothern Ocean.

Fig. 45. Family Ophiomusaidae O’Hara et al., 2018, Maximum likelihood (ML) tree based on partial COI sequences (bootstrap support values were generated with rapid bootstrapping algorithm for 1000 replicates). Abbreviations: NZ = New Zealand; SC = Sub-Clade; SCS = South China Sea.

Fig. 46. Family Ophiotomidae Paterson, 1985, Maximum likelihood (ML) tree based on partial COI sequences (bootstrap support values were generated with rapid bootstrapping algorithm for 1000 replicates). Abbreviations: IC = Inter Clade; SC = Sub-Clade; SCS = South China Sea.

Fig. 47. Family Ophiacanthidae Ljungman, 1867, Maximum likelihood (ML) trees based on partial 16S and COI sequences (bootstrap support values were generated with rapid bootstrapping algorithm for 1000 replicates). A. 16S ML. B. COI ML. Abbreviations: C = Clade; IC = Inter-Clade; NZ = New Zealand; SC = Sub Clade; SCS = South China Sea; TS = Tasman Sea.

Fig. 48. Family Ophiactidae Matsumoto, 1915, Maximum likelihood (ML) tree based on partial COI sequences (bootstrap support values were generated with rapid bootstrapping algorithm for 1000 replicates). Abbreviations: AUS = Australia; IC = Inter-Clade; NZ = New Zealand; PNG = Papua New Guinea; SC = Sub-Clade; SCS = South China Sea; TS = Tasman Sea.