Ophiacantha Müller & Troschel, 1842

Stöhr, Sabine, 2024, Taxonomic analysis of the genital plates and associated structures in Ophiuroidea (Echinodermata), European Journal of Taxonomy 933, pp. 1-98 : 37-39

Genus Ophiacantha Müller & Troschel, 1842

Fig. 16

Type species

Asterias bidentata Bruzelius, 1805 .

Examined species

Ophiacantha bidentata , O. abyssicola G.O. Sars, 1872 .

Oral GP

Pair close together, overlapping ventral disc scales. Rounded triangular or rectangular with median fold. Attached to distal point of oral shield with thickened edge. Large pore in inner side.

Adradial GP

Bar-like, with slightly widened distal end, articular structures as single dorso-distal condyle, bordered by curved groove with low protruding ventral stereom edge. Abradially a process and patches of denser stereom, where abGP attaches. Dorsal part of condyle meets flat surface of underside of RS.

Abradial GP

Thin, flat, curved scale, abradial edge strongly convex, adradial edge concave, with tapered, rounded proximal end, wider, slanting straight distal edge with flat or slightly domed articular surface. Adradial surface in distal part with conspicuous pore.

Oral shields

Hexagonal, wing-like, twice as wide as long, inner surface domed in centre, distal third of inner side thickened. Madreporite larger, wing-like with rounded lateral edges, strongly convex distal lobe, inner side flat on ‘wings’, thickened in centre and on lobe, which has a large hole, opening into a smaller hole (hydropore) in one latero-distal edge.

Radial shield

Narrow bar-like, distal end fan-shaped widened, small pore in distal part, straight distal edge, no specific articular structure.

Remarks

Two specimens of O. bidentata from Svalbard were analysed; the smaller one (11.5 mm dd) was dissected for this project and had narrower abGPs, a shorter but wider madreporite and slightly different adGPs ( Fig. 16A–L ) than the larger one (13 mm dd, Fig. 16M–O ), of which images existed prior to this project. It is unclear whether these differences are due to the small size difference or whether this is variation between individuals in this morphologically variable species (evidenced by the fact that it has been synonymized with five other nominal species ( Stöhr et al. 2022)). Since there is no geographic difference between these two specimens, it seems unlikely that these differences indicate different species. There is also some variation within the genus Ophiacantha . A specimen of O. abyssicola of similar size (13 mm dd) had narrower adGPs, smaller, less curved, more tapered abGPs, RSs with a triangular distal end with embossed part, and a madreporite with a large central hole.

Figures

Fig. 16. Ophiacanthidae Ljungman, 1867. SEM, unless otherwise noted. A–L. Ophiacantha bidentata (Bruzelius, 1805) (11.5 mm dd). A–B. Genital plates and radial shield in situ, micro-CT. C. adGP, abradial aspect. D. adGP, adradial aspect. E. abGP. F. Oral shield and oGP, in situ, bleached specimen, digital photo. G. Madreporite and oGP in situ, external aspect, micro-CT. H. Madreporite and oGP in situ, internal aspect, micro-CT. I. Radial shield, internal aspect. J. Madreporite, internal disto-lateral aspect. K. Oral shield and oGP (arrowheads), internal aspect.L. oGP, various aspects.M–O. O. bidentata (13 mm dd). M. adGP, adradial aspect. N. adGP, abradial aspect. O. abGP. P–T. O. abyssicola G.O. Sars, 1872. P. adGP, adradial aspect. Q. adGP, abradial aspect. R. abGP. S. Madreporite. T. Radial shield, internal aspect. Scale bars: 0.5 mm.