Ophiolimna bairdi, (LYMAN, 1883)

Stöhr, Sabine, 2005, Who’s who among baby brittle stars (Echinodermata: Ophiuroidea): postmetamorphic development of some North Atlantic forms, Zoological Journal of the Linnean Society 143 (4), pp. 543-576 : 552

OPHIOLIMNA BAIRDI (LYMAN, 1883)

( FIG. 5A–H )

The smallest individuals found measure about 1.0 mm dd, with ten arm segments. The dorsal disc is formed by numerous imbricating plates with almost imperforate stereom, among which no primary rosette can be distinguished ( Fig. 5A ). Short conical, rugose spinelets are scattered across the disc surface, each standing on an opening surrounded by a circle of smaller holes. The distal portion of the RSs is just visible above the arm, the proximal part covered by disc scales. The LAPs are strongly striated with transverse ridges and rows of fenestrations, each bearing three spines, the dorsalmost of which is longer than an arm segment, the ventralmost about half as long ( Fig. 5B ). The rounded triangular DAP with obtuse proximal angle and convex distal edge shows weak striations; plates of the following segments are separated by the LAPs. The VAPs are striated, with proximal angle, convex distal edge and strongly concave lateral edges; plates on following segments are separated by the LAPs ( Fig. 5C ). The first VAP is similar to the others, but with convex proximal edge. The TS is long, pointed and spine-like. The DP bears a spiniform pointed tooth and a similar MP to each side ( Fig. 5D ). The oral plate bears a wide low BS; adjacent oral plates are only parallel at their proximal ends, forming a wide angle distally, resulting in a jaw that is wider than long. ASs are longer than OS, separating it from the arm. The ASS is as long as a middle arm spine, pairs pointing towards each other, and not visible from above.

At 1.6 mm dd, the dorsal disc is formed by numerous overlappingscales, bearingadensecoveringofshortand sparsely distributed longer spines ( Fig. 5E ). The angle formed by adjacent oral plates has narrowed, forming a jaw that is longer than wide ( Fig. 5F ). The DP bears two spiniform MP1;there is a single conical MP2 on each edge of the oral plate replacing the BS, and proximal to the ASS a similar MP3 has formed on the AS ( Fig. 5G ). The ASS has shortened, but it is still longer than the MP, with which it forms a single row as the second TPo has moved close to the oral slit.The OS is triangular with convex distal edge, separated from the first VAP by the long ASs ( Fig. 5F, G ). The ventral disc is formed by small round overlapping plates with evenly distributed round perforations.

At 2.0 mm dd, dense granules and long spines completely obscure the disc scales. Granules have formed on the ventral disc scales and on the proximal end of the ASs ( Fig. 5H ). The row of MP consists of a small slightly pointed papilla on the DP, another similar papilla on the oral plate, a third on the distal AS and a larger, flat ASS. Each TPo bears a flat, pointed oval scale. Thus, all skeletal elements found in the adult are present and will only slightly change in shape or number during further growth.

Remarks: Ophiolimna bairdi can be identified by the striated arm plates, which are visible in all stages studied here.

SUBFAMILY OPHIOPLINTHACINAE PATERSON, 1985

Figures

Figure 5. Ophiolimna bairdi postlarval development. A–D, 1 mm dd postlarvae; A, dorsal; B, arm dorsal; C, arm ventral; D, ventral; E, 1.6 mm dd postlarva dorsal; F, 1.6 mm dd ventral; G, same, jaw; H, 2 mm dd postlarva. Abbreviations: BS, buccal scale; MP, mouth papilla; OP, oral plate; others as in Figs 1, 2. Scale bars in millimetres.