Limatula sp.

Oliveira, Cléo Dilnei De Castro & Absalão, Ricardo Silva, 2008, The genera Limatula and Limea (Mollusca, Pelecypoda, Limidae) from deep waters off Brazil, Zootaxa 1940, pp. 48-58 : 53-54

Limatula sp.

Figures 13–15

Description: Shell very fragile, white, small (height mean = 1.10mm ± 0.14 s.d.; range 1.00– 1.20mm; n=2), height/length ratio 1.47, slightly inequilateral, little inflated, outline suboval, dorso-central region smooth or with irregularly spaced concentric cordlets, region near the edge of the shell ornamented with strong axial ribs and concentric striae that cross the axial ribs, generating rounded nodules. The axial ribs are relatively equidistant and more visible on the ventral portion of the shell. Internally there are two slender axial ridges at the middle of the shell. Auricles small, symmetrical and slightly inclined in relation to the antero-posterior axis, forming an angle with the anterior and posterior margins. Subauricular sinus absent, anterior and posterior margins approximately symmetrical. Ventral margin somewhat rounded. Prodissoconch smooth, with conspicuous edge (mean 122.50µm ± 7.50 s.d.; range 115–130 µm; n=2). Interdissoconch not distinguishable. Umbones moderately prominent. Hinge plate large, without teeth. Ligamental pit broad, triangular.

Geographic range: Restricted to Campos Basin, Rio de Janeiro state, Brazil.

Material examined: IBUFRJ 17800, off Bacia de Campos (22°41'32" S, 40°00'47" W, 1906 m), 12. VI.03, [2 valves] .

Remarks: The main diagnostic characters are: (a) the axial ribs, which are evenly spaced but restricted to the mid-ventral edge of the valve (a view from inside is instructive, because the edge of the valve is crenulated only in this region and smooth in the remaining part); (b) there is an internal axial fold at the middle of the shell, barely visible externally; (c) the presence of a very large and smooth larval shell, not observed in any other species; and (d) there are very fine concentric striae that form small nodules (never spines nor scales) where they cross the axial ribs. We strongly suspect that this may be an unnamed species, but decided to wait for additional material to describe it.