Ophioplinthaca amezianeae O'Hara & Stoehr , 2006

Nethupul, Hasitha, Stoehr, Sabine & Zhang, Haibin, 2022, 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, ZooKeys 1099, pp. 155-202 : 155

Ophioplinthaca amezianeae O'Hara & Stoehr, 2006

Figs 8 , 9

Ophioplinthaca amezianeae O’Hara & Stöhr, 2006: 77-78, fig. 9D-G.

Material examined.

Northwest Pacific • 1 specimen; near Mariana Trench, Southwest of Guam Island, seamount; 11°40.33'N, 141°20.57'E; depth 3600 m; 27 November 2020; Collecting event: stn. SC040; Shenhaiyongshi msv leg; preserved in -80 °C; GenBank: OK043832 ; IDSSE-EEB-SW0109 .

Description.

Disc diameter 11.5 mm, arm base width 2.5 mm (Fig. 8 ).

Disc. Sub-pentagonal and incised interradially to 1/8 disc radius, creating five wedge-shaped lobes over each arm base in contrast to sunken center and interradii of disc (Fig. 8A, B ). Disc scales variable in size, overlapping, dense at center, and some scales bear spines (Fig. 8C ). Scales increase in size distalwards from disc center to distal end of radial shields interradially (Fig. 8C-G ). Disc spines at disc center 0.7-0.9 mm high, thick, with cylindrical to rounded base, tapering to a sharp point, or terminating in usually one or two small thorns, with additional irregular flanged thorns arising from lateral margins along the spine (Fig. 8D, E ). Disc spines on disc periphery and around radial shields, slightly smaller than center spines (0.5-0.7 mm in height), cylindrical, finely rugose, with thorny blunt tip (Fig. 8F, G ). Radial shields large, twice as long as wide, with acute proximal end, much wider convex distal end, and completely separated by disc scales (Fig. 8H ). Ventral disc covered by smaller scales compared to dorsal scales and overlapped, without or rarely bearing spines (Fig. 8B, I ). Genital slits conspicuous and extending from oral shield to periphery of disc (Fig. 8I ). Madreporite arrowhead-shaped, as wide as long, triangular with pointed proximal end, convex distal edge with thickened lateral margins (Fig. 8I ). Oral shield arrowhead-shaped, as wide as long, triangular with pointed proximal end, slightly concave lateral margins along adoral shields, lobed distal edge with rounded lateral margins (Fig. 8I ). Adoral shield 3 × as long as wide, with straight lateral margin, and pair of shields proximally connected (Fig. 8I ). Jaw longer than wide, and oral plates concealed by adoral shields (Fig. 8I ). Jaw bearing one large, pointed ventralmost tooth with three pointed, rod-like lateral oral papillae, shorter than ventralmost tooth, finely rugose, with wide, rounded base, and pointed tip (Fig. 8I ). One small, oval adoral shield spine at lateral margin of adoral shield at edge of second tentacle pore (Fig. 8I ).

Arms. Five slightly moniliform arms, with smooth plates. Dorsal arm plates fan- to bell-shaped, with truncated proximal end on first dorsal arm plate, but following plates with obtuse proximal end, straight to slightly convex proximolateral margins, and convex distal margin (Fig. 8J, K ). Dorsal arm plates at proximal end of arm barely separated, but distally widely separated (Fig. 8J, K ). First ventral arm plate trapezoid, as wide as long, with sunken proximal end, distally connected to second ventral arm plate (Fig. 8I ). Following ventral arm plates twice as wide as long, with obtuse proximal end, straight proximolateral margins, straight lateral angles, straight to slightly wavy distal end, and widely separated (Fig. 8L ). Lateral arm plates meeting above and below. Up to five arm spines: two dorsal spines, three arm segments in length, slender, thorny, laterally compressed with row of tall sharp thorns (Fig. 8J-M ); two ventral spines, two arm segments in length, thick, with blunt tip, rugose, and thorny surface (Fig. 8J, K ). First tentacle pore covered by one or two tentacle scales with rounded base and pointed tip (Fig. 8I ). Following tentacle scales with rounded base, spiniform, pointed tip and covered in irregular thorns, mostly on middle to distal half of arm (Fig. 8L ).

Color. In live specimen, orange-brown dorsal disc, pale color on arms and ventral disc, arm spines orange, and disc spines red (Fig. 8 ).

Ossicle morphology. Arm spine articulations well developed, four 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 (Fig. 9A ); large muscle opening, small nerve opening (Fig. 9A ). Proximal half of lateral arm plate internal surface with continuous ridge and prominent knob close to ventral edge forming vertebral articulation, shaped like a broad, nose-shaped beak (Fig. 9B ). Ventral arm spine thorny, with blunt apex, several longitudinal rows of perforations and small thorns (Fig. 9C ). Vertebrae with streptospondylous articulation, short, broad podial basin at proximal end, and narrow small distal end (Fig. 9D-H ). Dorsal end of vertebrae distally triangular and proximally flattened with longitudinal groove along midline (Fig. 9D, E ). Ventral end of vertebrae with broad ambulacral groove with lateral ambulacral canals (Fig. 9F-H ).

Distribution.

1618-3600 m depth, Southwest of Guam Island, Northwest Pacific, New Caledonia, New Zealand.

Remarks.

Ophioplinthaca amezianeae was described by O’Hara and Stöhr (2006), and recorded from deep waters in the South Pacific region. It can easily be delimited from most species in the genus Ophioplinthaca by disc spine, radial shield, and tentacle scale characters (Table 3 ).

Ophioplinthaca amezianeae from the present study is similar to the holotype description, but it differs slightly in the disc spine shape and number of arm spines on the lateral arm plate. However, the number of arm spines differs between individuals (6-10 arm spines) according to the description of paratype variations of O. amezianeae ( O’Hara and Stöhr 2006). The disc spines of our specimen are slightly thicker than in the holotype, but their shape and irregular flanged thorns arising from lateral margins along the spine are similar to the holotype description. The holotype is significantly larger than our specimen (14.5 mm disc diameter), and Ophioplinthaca species usually show high intraspecific morphological variation. Therefore, a slight difference in disc spine thickness can be considered as intraspecific morphological variation within O. amezianeae .

Figures

Figure 8. Ophioplinthaca amezianeae O'Hara & Stoehr, 2006 (IDSSE-EEB-SW 0109) A dorsal disc B ventral disc C center of the disc D-G disc spines H radial shield I oral frame J dorsal side of the arm base K dorsal arm L ventral arm, M lateral arm. Abbreviations: as adoral shield, ass adoral shield spine, dap dorsal arm plate, das dorsal arm spine, dp disc plate, gs genital slit, j jaw, lap lateral arm plate, m madreporite, 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 (H, I, K, M); 500 µm (C, J, L); 200 µm (D-G).

Figure 9. Ophioplinthaca amezianeae O'Hara & Stoehr, 2006 (IDSSE-EEB-SW 0109) A, B lateral arm plate C ventral arm spine D-H vertebrae D proximal view E distal view F ventral view G dorsal view H lateral view. Abbreviations: d dorsal, de depression, dist distal, lac lateral ambulacral canals, mo muscle opening, no nerve opening, pb podial basin, prox proximal, ri ridge, th thorns, v ventral, vs volute-shape. Scale bars: 800 µm (A-E, G, H); 500 µm (F).