Amphiura Forbes, 1843

Stöhr, Sabine, 2024, Taxonomic analysis of the genital plates and associated structures in Ophiuroidea (Echinodermata), European Journal of Taxonomy 933, pp. 1-98 : 54-56

Genus Amphiura Forbes, 1843

Fig. 25A–R

Type species

Amphiura chiajei Forbes, 1843 .

Examined species

Amphiura chiajei , A. filiformis (O.F. Müller, 1776) .

Oral GP

Amphiura chiajei : comma-shaped, flat, with oval proximal end, thin, needle-like appendix on inner distal end curved towards proximal end. Amphiura filiformis : elongated, curved or straight (in same individual), proximal end thickened, without distal needle-like appendix. Paired plates meet under the oral shield with convex edges towards each other ( A. chiajei ).

Adradial GP

Distal end widened with lateral lobes, long bar-like proximal shank, laterally curved with distal end above arm vertebrae, left and right plate almost meeting. Abradial distal lobe with dense, smooth, flat articular structure meeting abGP, distal end with protruding edge and curved depression with single round condyle meeting condyle on radial shield.

Abradial GP

Sabre-shaped, flat, thin, narrow blade, curved with dorsal edge concave, ventral edge convex, with longitudinal dorsal rim, at dorsal distal end a denser, smooth and slightly concave articular structure matching lobe on adGP, straight distalmost edge also joining distal end of adGP. Proximal end crosses proximal end of adGP. As long as adGP.

Oral shields

Inner side proximal part thickened, distal part thin, flat. Madreporite all over thicker, only margins thin, large opening in distal half, narrow slit in one proximolateral part.

Radial shield

Inner side distal end with large domed condyle, bordered by long narrow dorsal groove, proximal to condyle a large oval patch with finer stereom.

Remarks

Oral GP are visible externally in situ as large scale-like ossicles in Amphipholis squamata (Delle Chiaje, 1828) , Amphioplus congensis (Studer, 1882) , Acrocnida brachiata (Montagu, 1804) and in Silax cf. abditus Clark, 1970 ( Stöhr & O’Hara 2021: fig. 2e–f). In A. squamata , the adradial GP has a single distal lobe that articulates with the abradial GP, a single prominent condyle and a groove ( Fig. 25S ), similar to Amphiura . The abradial GP in A. squamata is sabre-like flat with longitudinal rim, not as strongly curved as in Amphiura . The oral GP of the two examined species of Amphiura differ greatly in shape and more data are needed to understand the variability of these ossicles. Perhaps, the soft, often scale-less ventral disc of A. filiformis has led to the evolution of the elongated oral GP for support of the genital slit.

Figures

Fig. 25. Amphiuridae Ljungman, 1867, SEM, unless otherwise noted. A–N. Amphiura chiajei Forbes, 1843. A–C. adGP and abGP in situ, micro-CT. D. adGP, dorsal aspect. E. adGP, ventral aspect. F. abGP, lateral aspect. G. Radial shield, inner aspect. H. Oral section, oGP. I. Oral GP. J–K. Digital images. J. Oral shield section, ventral disc scales removed, oGP. K. Oral GP in situ after removal of oral shield. L. Oral GP in situ (arrows), inside disc, micro-CT. M. Oral shield, inner aspect. N. Madreporite, inner aspect. O–R. Amphiura filiformis (O.F. Müller, 1776). O. adGP, dorsal aspect. P. adGP, ventral aspect. Q. abGP, lateral aspect. R. Oral GP. S–U. Amphipholis squamata (Delle Chiaje, 1828). S. adGP, lateral aspect. T. abGP lateral aspect. U. Radial shield, inner aspect. Arrowheads (H, J–K) mark oGP. Scale bars: A–H, J–L, O–Q=0.5 mm; I, M–N, R–U=0.1 mm.