Ophioplinthaca sp.
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publication ID |
https://dx.doi.org/10.3897/zookeys.1099.76479 |
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publication LSID |
lsid:zoobank.org:pub:A963E7C7-F1BF-4BF2-BB4F-A0CD5D319691 |
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persistent identifier |
https://treatment.plazi.org/id/55EFEFC4-751A-5C6F-B294-F0FE36784853 |
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scientific name |
Ophioplinthaca sp. |
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Figs 6 View Figure 6 , 7 View Figure 7
Material examined.
Northwest Pacific • 1 specimen; near Mariana Trench, Southwest of Guam Island, seamount; 12°36.44'N, 140°51.73'E; depth 2779 m; 23 September 2019; Collecting event: stn. SC038; Shenhaiyongshi msv leg; preserved in -80 °C; GenBank: OK043831 View Materials ; IDSSE-EEB-SW0108 GoogleMaps .
Description.
Disc diameter 9 mm, arm base width 2 mm (Fig. 6 View Figure 6 ).
Disc. Disc sub-pentagonal, incised interradially to nearly 1/5 disc radius, creating five wedge-shaped lobes over each arm base in contrast to sunken center and interradii of disc (Fig. 6A, B View Figure 6 ). Disc scales polygonal to rounded, somewhat similar in size, overlapping at center (Fig. 6C View Figure 6 ). Most disc scales bear one or two spines (Fig. 6C View Figure 6 ). Disc spines at center 0.25-0.3 mm high, smooth, or finely rugose, cylindrical single base with two or three sub-thorns, which bend into opposite directions (Fig. 6D, E View Figure 6 ). Some disc spines at center 0.2-0.3 mm high, smooth, or finely rugose, cylindrical with large, blunt tip (Fig. 6D, E View Figure 6 ). Disc spines around radial shields and periphery of disc 0.2 mm high, smooth, or finely rugose cylindrical, with blunt rounded tip (Fig. 6E-G View Figure 6 ). Disc scales interradially slightly increasing in size distalwards, and between radial shields, with one to four spines (Fig. 6G, H View Figure 6 ). Radial shields naked, ~ ¼ disc diameter in length, 1.5-2 × as long as wide, with acute proximal end, and wide, slightly convex distal end (Fig. 6G View Figure 6 ). Radial shields connected, but at proximal end separated by disc scales, and surrounded by disc spines (Fig. 6G View Figure 6 ). Ventral disc covered by small disc scales similar to interradial dorsal scales, bearing spines similar to periphery of disc (Fig. 6H-J View Figure 6 ). Genital slits conspicuous and extending from oral shield to periphery of disc (Fig. 6H-J View Figure 6 ). Madreporite arrowhead-shaped, as wide as long, pentagonal with pointed proximal end, lobed distal edge with thickened lateral margins (Fig. 6B View Figure 6 ). Oral shields twice as wide as long, diamond-shaped with obtuse proximal end, concave lateral margins along the adoral shields, distal edge with central lobe (Fig. 6I View Figure 6 ). Adoral shield 3 × as long as wide, slightly curved, proximal edge concave, distal edge convex, but near first ventral arm plate straight, and pair of shields proximally connected (Fig. 6I View Figure 6 ). Adoral shields enclose proximal edges of oral shield, and partly separate oral shield from arm by connecting to lateral arm plate of first arm segment (Fig. 6I, J View Figure 6 ). Jaw large, triangular, longer than wide (Fig. 6I View Figure 6 ). One slightly pointed, and large ventralmost tooth, longer and thicker than the four to five long, spiniform lateral oral papillae (Fig. 6I View Figure 6 ). One round, scale-like small adoral shield spine located at lateral margin of adoral shield at edge of second tentacle pore, in some jaw angles (Fig. 6I View Figure 6 ).
Arms. Five slightly moniliform arms, with smooth plates. Dorsal arm plates fan-shaped, as long as wide, widely separated, with convex distal edge, triangular proximal edge, straight lateral margins. Proximal edge of dorsal arm plate changes from obtuse to sharp triangular along arm (Fig. 6K View Figure 6 ). First ventral arm plate square to slightly trapezoid, as wide as long, with straight proximal and distal ends. Second and third ventral arm plate trapezoid, twice as wide as long, with straight proximal edge, slightly wavy distal edges, concave and diverging lateral edges (Fig. 6J View Figure 6 ). Second ventral arm plate contiguous with first ventral arm plate; following ventral arm plates as wide as long, pentagonal, with blunt to pointed proximal end, straight proximolateral margins, slightly curved lateral angles, straight to slightly curved inwards at distal end, and widely separated (Fig. 6J, L View Figure 6 ). Lateral arm plates meeting above and below (Fig. 6K-M View Figure 6 ). Up to six arm spines: three dorsal arm spines, two and a half arm segments in length, thorny or rarely smooth, lateral margins with scattered sharp thorns, apex pointed (Fig. 6M View Figure 6 ); three ventral arm spines, one to one and a half arm segments in length, pointed, and thorny or rough surface (Fig. 6K-M View Figure 6 ). First tentacle pore covered with one or two leaf-like, pointed tentacle scales (Fig. 6J View Figure 6 ). Following tentacle pores covered with one tentacle scale, as long as ventral arm plate, leaf-like, with thorny pointed tip (Fig. 6L View Figure 6 ).
Color. In live specimen, pale orange-brown (Fig. 6 View Figure 6 ).
Ossicle morphology. Arm spine articulations well developed, six in number, placed at slight angle to distal edge of lateral arm plate. A volute-shaped perforated lobe forms dorsal and distal parts of articulation (Fig. 7A View Figure 7 ). Arm spine articulation with large muscle opening and small nerve opening (Fig. 7A View Figure 7 ). Inner half of lateral arm plate with continuous ridge and prominent knob close to ventral edge forming vertebral articulation, shaped like a deep, nose-shaped beak (Fig. 7B View Figure 7 ). Dorsal arm spine thorny, with several longitudinal rows of perforations with widely spaced small thorns (Fig. 7C View Figure 7 ). Vertebrae with streptospondylous articulation, short, broad podial basin, and narrow small distal end (Fig. 7D-H View Figure 7 ). Dorsal end of vertebrae distally triangular and proximally flattened with longitudinal groove along midline (Fig. 7G View Figure 7 ). Ventral end of vertebrae with broad ambulacral groove, with lateral ambulacral canals (Fig. 7F, H View Figure 7 ).
Distribution.
2779 m depth, Northwest Pacific, near Mariana trench, Southwest of Guam Island.
Remarks.
Ophioplinthaca sp. shares morphological characters with many other Ophioplinthaca species, but can easily be delimited by the number of arm spines, disc spine shape, radial shields, and tentacle scale characters (Table 3 View Table 3 ). One of the distinguishing characters of this species is its smooth sub-thorny disc spines. According to the literature, only three Ophioplinthaca species have disc spines with sub-thorns on a single base ( Ophioplinthaca clothilde A.H. Clark, 1949, Ophioplinthaca grandisquama Chen, Na & Zhang, 2021a, and Ophioplinthaca manillae Guille, 1981), but the disc spines are covered with numerous spinules in these species.
The most similar species to Ophioplinthaca sp. is Ophioplinthaca clothilde sharing contiguous radial shields, similar number of arm spines (up to seven), number and shape of lateral oral papillae, similar tentacle scale, and separated ventral and dorsal arm plates, but differs in longer dorsal arm spines (up to four arm segments), disc spines with single cylindrical base ending in two or three crowns, or a stout disc spine with irregular crown of a dozen or more spinules, more or less ovoid radial shields with convex proximal side, slightly contiguous dorsal arm plates on proximal arm segments, and equal size of ventralmost tooth and lateral oral papillae. We refrain from naming our specimen, as these differences may suggest an undescribed species or fall within the insufficiently known variability of O. clothilde . This question may be answered, when more specimens have been collected, and molecular data are needed for O. clothilde .
Ophioplinthaca globata is similar to Ophioplinthaca sp. by having a similar number of arm spines (up to six), number of lateral oral papillae, and separated ventral and dorsal arm plate and shape, but differs by thorny disc spine and spine shape, separated radial shields and their shape, and tentacle scale longer than ventral arm plate. Ophioplinthaca laudator Koehler, 1930 shares with Ophioplinthaca sp. almost the same number of arm spines (up to seven), by size of radial shields, number and shape of lateral oral papillae, and separated dorsal and ventral arm plates, but differs in thorny disc spines, with two to three thorns or sub-thorns on their lateral surface, separated radial shields, and smooth arm spines. Ophioplinthaca grandisquama is similar to Ophioplinthaca sp. by having contiguous radial shields, closer number of arm spines (up to seven), and by the shape of arm and disc spines, but differs by tall (0.8 mm in high) long, thorny disc spines with two or three thorny sub-crowns, blunt tentacle scale, and contiguous ventral and dorsal arm plates. Ophioplinthaca manillae Guille, 1981 is similar to Ophioplinthaca sp. by having similar number and shape of arm spines, contiguous radial shields, shape of lateral oral papillae, and separated dorsal and ventral arm plates, but differs in an oval tentacle scale, and in height and shape of disc spines.
No known copyright restrictions apply. See Agosti, D., Egloff, W., 2009. Taxonomic information exchange and copyright: the Plazi approach. BMC Research Notes 2009, 2:53 for further explanation.
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