Limatula bisecta, Allen, 2010

Allen, J. A., 2010, The Recent species of the genera Limatula and Limea (Bivalvia, Limacea) present in the Atlantic, with particular reference to those in deep water, Journal of Natural History 38 (20), pp. 2591-2653 : 2621-2622

Limatula bisecta n. sp.

( figure 35 )

Type locality. Chain sta. 309, 52 ‡ 21.1 ’ N, 12 ‡ 07.4 ’ W, 479 m.

Holotype. BMNH.

Material examined. Chain sta. 309, 52 ‡ 21.1 ’ N, 12 ‡ 07.4 ’ W, 479 m, 3 spec.

Distribution. Known only from one upper slope station, off south-west Ireland.

Description ( figure 35 ). Shell very small (max. recorded height 2 mm), height/ length ratio 1:0.70, very fragile, moderately inflated, equivalve, almost equilateral, transparent, ornamented with one close-set pair of axial ribs either side of a fine axial channel, faint suggestion of six or seven ventral marginal ribs, few very fine concentric growth lines and hardly visible fine marginal striae where marginal ribs occur, ventrally broadly rounded, ears not extended and without ornament, no anterior subauricular sinus, very shallow suggestion of posterior auricular sinus; umbo moderately prominent; hinge line approximately straight; ligament short and lozenge-shaped. Prodissoconch I length~130 M m; interdissoconch ca 0.25 mm.

Anatomy. The mantle margin is relatively broad and each middle sensory fold bears 12–13 very small papillate tentacles, including a small anal tentacle. The posterior adductor is small and circular in cross-section. As far as can be seen through the shell, the gill is reduced to one demibranch but in other respects the anatomy is similar to that of other species described above.

Remarks. Although it is possible that this may turn out to be the juvenile of a larger species, no other described species is characterized by a fragile transparent shell with a single central medial channel. It is named after this latter feature.

Figures

FIG. 35. Limatula bisecta. Sta. 300 lateral view from the right side with some detail of the mantle tentacles as seen through the transparent shell. Scale bar: 1 mm.