Ophiura cf. trimeni Bell, 1905

O’Hara, Timothy D. & Thuy, Ben, 2022, Biogeography and taxonomy of Ophiuroidea (Echinodermata) from the Îles Saint- Paul and Amsterdam in the southern Indian Ocean, Zootaxa 5124 (1), pp. 1-49 : 8-10

Ophiura cf. trimeni Bell, 1905

Fig. 3C–E

Material examined. MD 50 DC6, MNHN IE.2009.1610 (2). MD 50 DC64, MNHN IE.2009.1612 (1). MD 50 DC91, MNHN IE.2009.1613 (6); MNHN IE.2009.1620 (2). MD 50 DC137, MNHN IE.2009.1621 (3); MNHN IE.2009.1611 (1). MD 50 DC144, MNHN IE.2009.1622 (1). MD 50 DC167, MNHN IE.2009.1614 (3).

Distribution. SPA (720–1675m).

Remarks. These specimens belong to the Ophiura ooplax / trimeni group of species characterised by ovoid DAPs that rapidly become separate, three arm spines, the uppermost lengthened and thickened basally, the elongated ‘eland-horn’ shaped radial shields ( Fig. 3D ), wide oral shields with a notch at the distal end of each side, and the kite-shaped basal VAPs becoming wide and rhomboid by the 4–6th plate with a rounded distal lobe ( Fig. 3E ). There are some ontogenetic changes. Younger specimens have been reported to have small spines on the disc (or at least they survive collection better) ( Fell 1952; Mortensen 1933a), the radial shields are more rounded and distally contiguous, and the arm comb is more visible from the dorsal side.

This cryptic complex has been principally recorded from around Japan ( O. ooplax H.L. Clark, 1911 ), southern Australia / New Zealand ( O. ooplax chathamensis Fell, 1952 ) and South Africa ( O. trimeni ). O’Hara et al. (2013, 2017) also reported specimens from tropical NW Australia that formed a distinct mitochondrial DNA clade compared to O. ooplax chathamensis . The only other tropical record is from off southern coast of Mindanao ( Koehler 1930). Currently, there are no known morphological characters that can reliably distinguish any of these populations.

For the present, the MD 50 specimens are identified as Ophiura cf. trimeni . They differ from typical trimeni , O. ooplax and O. ooplax chathamensis in having shorter, wider radial shields that have a rounded rather than acute proximal angle. The MD 50 specimens were collected somewhat deeper (720–1685 m) than is typical for either O. trimeni or O. ooplax , which are rarely found below 1000 m (although see Clark 1923; McKnight 1967 for deep records).

O. ooplax was originally described as an Ophiocten and many characters in the new material are reminiscent of that genus, including the elongated upper arm spine and the rounded distal lobe on the VAPs. However, it differs in having ovoid DAPs that are separated soon after the disc (trapezoid and contiguous in Ophiocten ), and numerous tentacle scales around the second oral and basal arm tentacle pores.

Figures

FIGURE 3. (A–B) Ophiura ljungmani, MNHN IE.2009.1623,A:dorsal and B: ventral views.(C–E) Ophiura cf. trimeni, MNHN IE.2009.1620, C: dorsal outline, D: dorsal and E: ventral views. (F–H) Ophioplinthus sp., juvenile, MNHN IE.2009.1619, F: dorsal outline, G: dorsal and H: ventral views.