Amphiophiura Matsumoto, 1915

Stöhr, Sabine, 2024, Taxonomic analysis of the genital plates and associated structures in Ophiuroidea (Echinodermata), European Journal of Taxonomy 933, pp. 1-98 : 17-19

Genus Amphiophiura Matsumoto, 1915

Fig. 4

Type species

Ophioglypha bullata Thomson, 1877 .

Examined species

Amphiophiura latro (Koehler, 1904) , A. insolita (Koehler, 1904) .

Oral GP

Absent.

Adradial GP

Amphiophiura latro : spatulate, stout, half as wide as long, proximally tapered, articular structures flat patches of finer meshed stereom. Abradial side with longitudinal groove and large hole in distal part. Twice as long as abGP. Amphiophiura insolita : stout, wedge-shaped, half as wide as long, dorsally concave, ventrally convex, proximally tapered, distal end widened, articular surface to RS flat, extending to middle of plate, protruding laterally. Abradial ventrodistal part with articular structure with abGP of coarse stereom.

Abradial GP

Amphiophiura latro : shorter than adGP, twice as high as long. Exposed distal end inflated, slightly curved, with tuberculous stereom, small round articular holes without lobes for genital papillae, inner part with simple stereom, as high and long as outer part, but much thinner. Amphiophiura insolita : shorter than adGP, broad diamond-shaped. Exposed distal end slightly curved, with weakly tuberculous stereom, small round articular holes without lobes for genital papillae; inner part with simple stereom, proximal end tapered, proximal third flat, thinner than inflated distal two thirds. Adradial edge slanting, a round depression with coarse stereom close to edge with articular structure to adGP.

Oral shields

Amphiophiura latro : covering large part of ventral disc, inner side with one round spur on either side of proximal part. Madreporite with large hole in proximal part between spurs, opening to one side. Amphiophiura insolita : covering all of ventral disc. Madreporite with large hole near proximal edge, no side opening.

Radial shield

Amphiophiura latro : articular structures a shallow depression and a small round, finer meshed patch at the distal internal edge. A round, finer meshed patch in the centre of the inner surface. Amphiophiura insolita : articular structure a wide flat surface extending from distal edge to middle of plate, thicker than proximal part. Lateral in distal edge a short slit.

Remarks

The genus Amphiophiura Matsumoto, 1915 is regarded as paedomorphic ( Stöhr & Martynov 2016), but contrary to expectations, the genital plates are large and well differentiated. There is a stout conical adGP with a flat articular structure, and, in contrast to most other species, a much larger abGP, partially exposed at the disc edge, bearing an arm comb of genital papillae. Although the arm comb is similar to that of Ophiura , species in that genus have an exposed cup-shaped abGP that does not extend far into the disc. In several species of Amphiophiura the genital slit borders the large oral shield laterally.

Figures

Fig. 4. Ophiopyrgidae Perrier, 1893, Amphiophiura Matsumoto, 1915, SEM images, unless otherwise noted. A–G. A. latro (Koehler, 1904). A. Arm base, lateral aspect. B. abGP, radial aspect. C. abGP, abradial aspect. D. adGP, abradial aspect. E. adGP, adradial aspect. F. Radial shield, inner (ventral) aspect. G. Madreporite, inner (dorsal) aspect. H–P. A. insolita (Koehler, 1904). H. Radial shield, inner aspect. I. adGP, abradial aspect. J. adGP, dorsal view. K. adGP in situ, micro-CT. L. abGP in situ, micro- CT. M. abGP, abradial aspect (distal part with larger pores is exposed at disc edge). N. abGP, adradial aspect. O. abGP, distal end, arrowheads mark articular structures for genital papillae. P. Madreporite, inner aspect. Scale bars: A–O=0.5 mm; P=1 mm.