Ophiocymbium ninae, Martynov, 2010

Martynov, Alexander, 2010, Reassessment of the classification of the Ophiuroidea (Echinodermata), based on morphological characters. I. General character evaluation and delineation of the families Ophiomyxidae and Ophiacanthidae 2697, Zootaxa 2697, pp. 1-154 : 58-60

Ophiocymbium ninae sp. nov.

Figures 4L,T; 12F–G, K–L; 17E, H–J; 41; 55I–N

Material. Holotype, ZMMU D-802, R / V “Vityaz”, cruise 45, sta. 6109, 15 May 1969, 56°14,1' N 139° 44,0' W – 56°12,7' N 139° 43,4' W, depth 3450–3460 m, grab dredge "Ocean". 13 dried paratypes, ZMMU D-803, same sta. as the holotype. 9 dried paratypes, ZMMU D-804, R / V “Vityaz, cruise 29, sta. 4213, 34° 54' N 123° 55' W, depth 4231– 4200 m, Sigsbee trawl. 3 ethanol paratypes, ZMMU D-805, R / V “Vityaz, cruise 29, sta. 4213, 34° 54' N 123° 55' W, depth 4231– 4200 m, Sigsbee trawl.

Etymology. This species is named in honour of ophiuroid taxonomist Nina Litvinova (Moscow, P.P. Shirshov Institute of Oceanology), whose efforts in describing the deep-water Ophiuroidea has elucidated their importance for taxonomy and phylogeny.

Description of the holotype. The disk, 6.8 mm dd, is pentagonal. The disk plates are numerous, somewhat obscured by thin wrinkled skin, when dried. Radial shields are very small irregular plates, similar in size to disk scales, placed at the edge of the disk and scarcely visible (see a detailed radial shield description under paratype variations). The whole dorsal side of the disk is covered with short cylindrical or subconical, sparsely placed spinelets. The interradii are slightly swollen, ventrally covered with few spinelets. Each jaw bears apically a cluster of 3–4 spiniform teeth or apical papillae. The 3–6 lateral papillae together with the adoral shield papillae are placed along both edges of each jaw in a characteristic, slightly curved row around the second tentacle pore. The adoral shield papillae are long, flattened, similar in size and shape to the arm spines, 2–3 in number in most interradii, five in one interradius. The paired proximalmost oral papillae are placed laterally. Between lateral oral papillae and second tentacle pore the jaws form a rectangular border, which is superficially similar to the block-shaped oral papillae. Numerous spiniform teeth are distributed in a cone-shape, tapering dorsalwards. There are approximately 10 teeth (including apical papillae) on each dental plate. The oral shield is wide, triangular with straight or slightly convex, rather long distal edge, as long as wide, completely separated from the first lateral arm plate by the adoral shields. Distally the oral shield adjoins a supplementary narrow elongated plate or just an elevation formed by adjacent interradial scales. The madreporite has a conspicuous swollen round area occupying a considerable part of its surface. The adoral shield is wing-shaped laterally, widely adjoining the arm, rapidly tapering towards to the midline of the jaws, retaining thus only a narrow bar between jaws and oral shield. True genital slits are barely conspicuous, small openings under the adoral shields, but a long furrow between the most proximal arm segments and the ventral interradius forms a false slit.

Arm length is about 1.7 times the disk diameter. On all arms the most proximal dorsal plates are absent for two-three segments, replaced by a covering of small disc scales. The dorsal arm plates are well developed but rather small, triangular, tapered and increasingly pentagonal towards the middle of the arm, well separated on all segments (for about half of the length of the dorsal arm plate proximally and length of the dorsal plate distally). All dorsal arm plates have pointed proximal and convex distal edges. Arms have weakly developed nodes, but arm spine articulations are placed on lateral plates without forming an elevation. Laterally between two adjacent lateral plates there is a narrow space of uncovered soft tissue. There are two spines on the first arm segment, three on proximal segments under the disk, afterwards four to five and then three distally. The first dorsal spine is slightly longer than the other ones proximally and medially. Spines are flattened, pointed apically. There are no hook-shaped spines. The first ventral arm plate is broadly triangular, the second has straight distal and proximal edges; further ventral arm plates have a characteristic pole-axe shape throughout most of the arm length, with a triangular proximal edge, whereas distally they vary from straight to slightly concave or convex with a small elevation. Ventral plates throughout the length of the arm are contiguous, except for the first two segments. The tentacle pores are large throughout the entire arm length. Basally on the parts of the lateral plate encircling the tentacle pores there are one, or rarely two larger, long, flattened, pointed tentacle scales. On most arm segments there is one tentacle scale. Distally the tentacle scale becomes small and spiniform. The tentacle scales are shorter than arm spines, but conspicuous and capable of covering the whole tentacle pore. Many of the tentacle scales are broken or have fallen off. There are no tentacle scales on the ventral arm plates.

Paratype variations. A paratype, from the same station as the holotype, 7.0 mm dd, is similar with the holotype, but has a markedly pentagonal disk and some other minor differences. Numerous disk scales are clearly embedded within a thin skin. Apical papillae (teeth) are less numerous and thinner, up to 7 in number. A single spiniform tooth in the dorsal part of the dental plate is markedly longer than (up to twice) the apical papillae. The distalmost oral papillae are block-shaped, but short. The following two oral papillae are short and spiniform. The first 1–2 proximal segments near the disk have no dorsal plates and are covered with small scales and skin. The madreporic oral shield is similar in shape to the others but with a swollen area in the middle. Genital slits are very short, placed just below adoral shields, a narrow adradial genital plate is evident in the distal part of the ventral side of the disk, but does not support the walls of the genital slits. The abradial genital plate is absent. Radial shields are very small and inconspicuous. On the 1–2 proximal lateral arm plates under the disk there are two flattened, apically pointed spines, on the proximal and middle lateral plates there are 4–5 spines. Although many tentacle scales are missing, three are present on the most proximal arm segments and some second and third segments. The ventralmost of these three scales is placed at the border of lateral and ventral arm plates, but still on the lateral plate.

A small paratype, from the same station as the holotype, 4.0 mm dd, is similar to the holotype, except for the pentagonal disk and some other differences. There are obvious primary plates joined in a flower-shaped structure. Few disk spines are visible. The radial shields are more evident than in the holotype and other paratypes. Dorsal arm plates proximally are almost rhomboid with rounded angles. Medially and distally dorsal arm plates become almost ovoid. The distance between two adjacent dorsal arm plates proximally is about equal to the dorsal plate length, whereas distally it is up to twice the length of the dorsal plate. Apical papillae (teeth) are considerably fewer than in the holotype and there is an obvious larger middle apical papilla and 1–3 smaller and thinner lateral apical papillae. A single spiniform tooth in the dorsal part of the dental plate is present only in some interradii and is similar in size to the middle apical papilla. The distalmost oral papillae are block-shaped relatively long elevations. The single pair of oral papillae are rectangular and pointed, somewhat similar in shape to the buccal scales of Amphiuridae and Ophiactidae . The first 1–2 proximal segments near the disk lack dorsal plates and are covered with small scales or almost naked skin exposing the vertebrae. The madreporic oral shield does not differ from the remaining oral shields. Genital slits in most interradii are longer than in the holotype, whereas in one interradius they are small. A narrow adradial genital plate is obvious in the distal part of the ventral side of the disk, but does not support the walls of the genital slits. The abradial genital plate is absent. On the 1–2 proximal lateral arm plates under the disk there are 2–3 flattened, apically pointed spines, on proximal and middle lateral plates four, and distally three spines. Proximally there are 1–2 large, flattened tentacle scales, which become smaller medially and disappear entirely distally. There are no hook-shaped spines.

Internal and microstructural characters. The radial shield is a very small irregular plate, with slightly elevated articulation surface ( Fig. 4T). The articulation surface of the abradial genital plate does not have any distinct condyles ( Fig. 4L). The abradial genital plate is absent. Jaws are slightly elongated ( Figs 12K, L). Adradial sides of the jaws distally bear few indistinct straight folds and irregularly-shaped tubercles ( Fig. 12L). The dental plate is devoid of folds, with few small rounded sockets ( Figs 12F, G). Arm spine articulations are well defined and belong to the double-opening type ( Figs 55M, N). The muscle opening is placed on a distinct round or elongated elevation, some articulations are slightly ribbed distally. Nerve opening placed laterally below the level of the muscle opening. Vertebrae rather short, not keeled and with well developed zygospondylous articulation ( Figs 41G, 17E, J). Vertebral dorsal median groove is distinct ( Figs 41G, 17E). Podial basins are large ( Figs 41F, 17H).

Remarks. Ophiocymbium ninae sp. nov. is clearly distinguished from both Ophiocymbium cavernosum and Ophiocymbium tanyae sp. nov. by the presence of conspicuous short disk spinelets, less evident distal block-shaped oral papillae, and the shape of the arm spine articulations and vertebrae. Ophiocymbium tanyae sp. nov. also differs from Ophiocymbium ninae sp. nov. by the absence of the adradial genital plate.