Ophiactis Lütken, 1856

Stöhr, Sabine, 2024, Taxonomic analysis of the genital plates and associated structures in Ophiuroidea (Echinodermata), European Journal of Taxonomy 933, pp. 1-98 : 56-58

Genus Ophiactis Lütken, 1856

Fig. 27

Type species

Ophiactis krebsii Lütken, 1856

= Ophilepis savignyi Müller & Troschel, 1842 .

Examined species

Ophiactis abyssicola (M. Sars, 1861) , O. savignyi .

Oral GP

Drop-shaped, round with small lobe at one end (unknown if proximal or distal). (Only examined in O. abyssicola .)

Adradial GP

Bar-like, with longitudinal dorsal furrow, distally widened, somewhat thicker than proximal shank, single condyle bordered by deep groove, proximal to condyle a protruding patch of finer stereom articulating with abGP, separated from condyle by deep groove, forming wrench-shaped adradial distal end.

Abradial GP

Two thirds as long as adGP, thin, broadly sickle-shaped, strongly convex ventral edge, distally twice as wide as proximally, distal edge straight and articulating with adGP.

Oral shields

Distal half of inner side thickened, proximal half flat and thin. Madreporite thick, lateral margins flat, two large openings, one in centre, one offset from centre in proximal half.

Radial shield

Inner side with distal condyle, bordered by curved groove, proximal to condyle a round, rough patch.

Remarks

The presence of oral GPs was also observed externally in O. macrolepidota Marktanner-Turneretscher, 1887 and O. savignyi . These fissiparous species are not well suited for the examination of dissociated ossicles, because most individuals are a composite of parts in different stages of regeneration, and therefore the ossicles vary considerably in size and shape within an individual.

Figures

Fig. 27. Ophiactidae Matsumoto, 1915, SEM, unless otherwise noted. A. Ophiactis savignyi (Müller & Troschel, 1842), genital plates in situ, micro-CT. B–L. Ophiactis abyssicola (M. Sars, 1861). B. adGP and adGP articulated. C. Radial shield, internal aspect. D–E. adGP, dorsal aspect. F. adGP, ventral aspect. G. abGP, abradial aspect. H. adGP, ventrolateral view (from other, smaller specimen). I. oGP in situ (arrowheads, digital image), oral shield removed. J. Oral shield, internal aspect. K. Madreporite, internal aspect. L. oGP. Scale bars: A, J–L= 0.1 mm; B–I= 0.5 mm.