Amphilimna Verrill, 1899

Stöhr, Sabine, 2024, Taxonomic analysis of the genital plates and associated structures in Ophiuroidea (Echinodermata), European Journal of Taxonomy 933, pp. 1-98 : 48

Genus Amphilimna Verrill, 1899

Fig. 22

Type species

Ophiocnida olivacea Lyman, 1869 .

Examined species

Amphilimna olivacea .

Oral GP

Large, rectangular, flat, thin, with round, elongated proximal lobe. Almost vertical along proximal abradial bursa edge.

Adradial GP

Bar-like with widened distal end. Articular structures a low condyle, bordered by shallow groove and low edge. Proximal to condyle a rounded abradial process to which the abGP articulates ventrally, a round depression of coarse stereom and a small pore. Proximal part twisted.

Abradial GP

Twisted s-shape, thin, with distal adradial appendix, one third as long as plate, folded proximalwards and fold articulates with adGP, folding around flat extensions of lateral arm plates. Distal edge straight. Large adradial plates (flat and interlocked arm spines) bordering genital slit fold over abGP and under appendix, similar enlarged disc scales fold over the slit edge abradially, on their inner side supported by the abGP.

Oral shields

Flat, on distal part a spur on each side, offsetting distal lobe from proximal part. Madreporite slightly inflated in centre, with large opening between distal lateral spurs, proximal to large hole stereom wider meshed with pores. Externally a single hydropore at distal edge, offset from centre.

Radial shield

Inner side with distal flat condyle, bordered by curved groove. Distal to RS midline a rough round patch.

Remarks

The shape of the abradial GP sets Amphilimna olivacea apart from all other here examined species. The peculiar shape matches the specialized lateral arm plates, which are blade-like flat and form the adradial border of the s-shaped genital slit. The genital plates of A. multispina Koehler, 1922 are similar to those of A. olivacea ( Martynov 2010) , but their shape is unknown for other species in the genus. Contrary to the original description of A. olivacea , no genital plate is exposed to the outside ( Lyman 1869), as is evident from the micro-CT reconstruction.

Figures

Fig. 22. Amphilimnidae O’Hara, Stöhr, Hugall, Thuy & Martynov, 2018, Amphilimna olivacea (Lyman, 1869). A–C =micro-CT; D–H, J–N =SEM; I=digital image. A. adGP, abGP, wing-like LAPs in situ. B. Detail of A, different angle. C. adGP in situ, dorsal aspect. D. adGP, adradial aspect. E. Radial shield, inner aspect. F. RS articular structures. G. abGP, abradial aspect. H. abGP, adradial aspect. I. Jaw in situ, bleached. J. Oral shield, inner aspect. K–L. oGP inner/outer aspects (unclear which is which). M. Madreporite, inner aspect. Scale bars: A–C, F, J–M =0.2 mm; D–E, G–I =0.5 mm.