Ophioderma Müller & Troschel, 1840

Stöhr, Sabine, 2024, Taxonomic analysis of the genital plates and associated structures in Ophiuroidea (Echinodermata), European Journal of Taxonomy 933, pp. 1-98 : 31-33

Genus Ophioderma Müller & Troschel, 1840

Fig. 13

Type species

Asterias longicauda Bruzelius, 1805 .

Examined species

Ophioderma longicaudum , O. zibrowii Stöhr, Weber, Boissin & Chenuil, 2020 , O. africanum Stöhr, Weber, Boissin & Chenuil, 2020 ( Stöhr et al. 2020).

Oral GP

Comma-shaped, ventrally flat, dorsal keel on distal part, three times as long as greatest width, half as long as proximal genital slit, curved along slit, with rounded proximal end and pointed distal end, longitudinal row of about six small pores. Pair distally at a wide angle from each other, proximally close but separated. Proximal part covered by oral shield. (Only examined in O. longicaudum ).

Adradial GP

Rod with bulbous distal end, flatter proximal to bulbous part, tapering proximalwards, ventral edge convex, dorsal edge straight. Bulbous end composed of a domed condyle and a flat condylar process, adradial one surrounded by a circular groove. In situ, this groove and a corresponding groove and condyle on adradial inner surface of radial shield connected by muscle fibres. A large hole near base of adradial condyle.

Abradial GP

Trapezoid, with straight distal and dorsal edges, ventral and proximal edges angling upwards. Adradial surface with conspicuous pore in distal part, abradial surface with shallow longitudinal groove. Articulating with adradial GP on its abradial side, at proximal border of abradial condyle.

Oral shields

Rounded triangular, with groove in distal edge. Inner surface with scattered small pores, lateral edges in distal half depressed, distal part raised as a ridge with straight-edged wide median process. Madreporite inner surface with rough stereom on raised middle part, denser stereom on flat outer edge and with 2–3 low spurs, distally a thickened spur to either side of a large hole that opens to one side in a smaller hole (hydropore), bordered distally by rectangular process. Externally madreporite with deep, round depression in distal half, groove in distal process, hydropore in one side.

Radial shield

With two large, low condyles of denser stereom occupying most of inner distal surface of shield, proximal to and between them a large opening and proximal to that a round, slightly depressed patch of smaller pore stereom. Adradial condyle bordered by a groove.

Remarks

Matsumoto (1917) stated: “In Ophioderma , the genital plate and scales of the same side of a radius are soldered together at the middle, so that the genital slit is divided into two secondary pores, an inner and an outer.” ( Table 1 ). He probably referred to the disc scales, not the “genital scale” (= abradial GP), because there is only a single short “genital scale” at either side of an arm. It is unclear what he meant by “soldering”, but GPs and disc scales fall apart in bleach, suggesting no hard parts are fused, and in the 3D reconstructions, there is a gap between vertebrae and adGP. The body wall forms a wide bridge across the genital slit, dividing it into a proximal and a distal opening. The abradial GP is less than half as long as the adradial GP and supports only the distal genital opening; the proximal one is supported abradially by the oral GP. The three species closely related to O. longicaudum for which ossicle data are available are all highly similar in the examined structures.

Figures

Fig. 13. Ophiodermatidae, Ljungman, 1867, Ophioderma longicaudum (Bruzelius, 1805), SEM, unless otherwise noted. A–C. adGP and abGP in situ, in various orientations, micro-CT. D. adGP and abGP in situ. E. adGP, abradial aspect. F. abGP, arrow points to corresponding articular structure on adGP. G. adGP, adradial aspect. H. adGP, dorsal view. I–J. adGP, distal aspect. K. Radial shield, inner side. L. Oral shield, inner side. M. Jaw (arrowhead marks oGP), bleached, digital photo. N. Jaw with oral shield removed, oGP exposed (arrowheads), bleached, digital photo. O. Pair of oGP, ventral aspect. P. oGP, lateral aspect. Q. Madreporite, inner side. Scale bars: 0.5 mm.