Amphiura gymnogastra Lütken & Mortensen, 1899

Granja-Fernández, Rebeca, Hendrickx, Michel E., Rangel-Solís, Pedro Diego & López-Pérez, Andrés, 2023, Deep-sea Ophiuroidea (Echinodermata) collected during the TALUD cruises in western Mexico, Zootaxa 5259 (1), pp. 1-71 : 50

Amphiura gymnogastra Lütken & Mortensen, 1899

Fig. 15A‒F

Amphiura gymnogastra Lütken & Mortensen, 1899: 145‒146 , pl. 9, figs. 6‒8.— H.L. Clark 1917: 437.

Hemilepis gymnogastra . Fell 1962: 10, 22.

Material examined. Four individuals at two stations. TALUD XII, Sta. 13, 3 ind. (ICML-EMU-11148-A); Sta. 26, 1 ind. (ICML-EMU-11148-B).

Comparative material. Syntypes, 5 ind.: MCZ OPH-1321 , USNM 19526 (Supplementary file 2) .

Description (ICML-EMU-11148-A). DD = 6.6 mm. Disc malformed. Dorsal disc covered by imbricated scales, those surrounding RS larger, integument distally. Primary plates not evident. RS triangular with rounded edges, prominent distal end, in contact only distally, the rest separated by scales ( Fig. 15A ). Ventral interradii covered by scale-less integument ( Fig. 15B ). OSh broader than long, spearhead-shaped with strongly convex proximal and lateral edges and distal lobe. Madreporite rounder and larger than OSh. AdSh scalene triangular, separated. Jaws bearing three oral papillae at each side; AdShSp scale-like round; BSc slender, pointed; IPa quadrangular with rounded edges. vT quadrangular ( Fig. 15C ). Arms slender. DAP broader than long, oval, contiguous ( Fig. 15D ). VAP longer than broad, pentagonal, contiguous. LAP with 5‒6 ArSp, small (approximately 1.2 arm segment in length), conical with blunt tip; ventralmost the longest, dorsalmost the thinnest and shortest. Tentacle pores with two oval TSc, adradial longer ( Fig. 15E ). Color pattern in dorsally and ventrally beige-whitish (ethanol preservation) ( Fig. 15A‒F ).

Habitat and distribution. Mexico, Panama, and the Galapagos Islands; 549‒ 2,323 m depth, hard and muddy substrates (Lütken & Mortensen 1899; H.L. Clark 1911; Maluf 1988; see Remarks). The material examined was collected off Colima and Guerrero; 1,199 ‒1,956 m depth.

Remarks. Specimens of Amphiura gymnogastra tend to lose their disc and oral papillae very easily, thus making correct identification very complicated. This species can have a dorsal disc covered with imbricated scales or with scales and small areas near the margin of the disc with only integument.Areas with integument in the dorsal disc can result from the pressure by the ventral disc on the dorsal side during the sampling process. Amphiura gymnogastra has been previously recorded off Panama and the Galapagos Islands (Lütken & Mortensen 1899; H.L. Clark 1911), and records off central and southern Mexico represent a significant extension of its northernmost distribution limit to 18º33′27″N, 104º28′21″W. Available material of A. gymnogastra is currently limited to 13 specimens: 1) the type material, which is not in good condition (MCZ OPH-1321, two specimens; USNM 19526, three specimens), 2) one lot from the Galapagos Islands (USNM E669, four specimens), and 3) two lots from the TALUD cruises (ICML -EMU-11148-A, three specimens; ICML-EMU-11148-B, one specimen).

Figures

FIGURE 15. Amphiura gymnogastra Lütken & Mortensen, 1899 (ICML-EMU-11148-A, DD = 6.6 mm). A, Dorsal disc; B, Ventral disc; C, Mouth; D, Dorsal arm; E, Ventral arm; F, Dorsal view. Amphiura (Amphiura) diomedeae Lütken & Mortensen, 1899 (ICML-EMU-11155, DD = 12 mm). G, Dorsal disc; H, Ventral disc; I, Mouth; J, Dorsal arm; K, Ventral arm; L, Dorsal view.