Limea argentineae, 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 : 2626-2628

Limea argentineae sp. nov.

( figures 42 , 43 )

Type locality. Argentine Basin , 36 ‡ 32.6 ’ S, 10 ‡ 23.4 ’ W, 993 m.

Holotype. BMNH.

Material examined. Atlantis II sta. 237, 36 ‡ 32.6 ’ S, 53 ‡ 23.0 ’ W, 993 m, 2 spec.

Distribution. Taken at one station, at mid-slope depth, in the Argentine Basin.

Description ( figures 42 , 43a, b ). Shell moderately small (max. recorded height 6.5 mm), height/length ratio 1:0.78, relatively strong, not inflated, equivalve, asymmetrical, white, ca 22 broad, flattened radial ribs, central ribs strongest, anterior and posterior ribs grade until barely visible, fewer anteriorly than posteriorly, numerous concentric ridges with fine raised edges, most pronounced across radial ridges, concentric ridges extend over entire shell, two radial ribs extend from umbo to ventral-most point of shell margin, remainder do not extend to umbo, dorsally becoming more faint, interdissoconch ill-defined but with concentric ridges; ears of shell well-developed each with six or seven vertical ridges, subauricular sinuses shallow; umbos prominent; hinge margin sharply defined, at oblique angle to axis of main rib, anterior and posterior sections at slight angle to each other, hinge plate broad with 18–19 short, weak vertical teeth set in crescent-shaped anterior and posterior plates either side of central triangular ligament, plates supported by stout, broad shell margins. Prodissoconch I length~ ca 240 M m; interdissoconch ca 0.75 mm.

Anatomy ( figure 44a, b ). Mantle margins relatively narrow, each bears eight small marginal tentacles in juvenile specimen (height 2.5 mm) and one posterior anal tentacle no larger than other tentacles; posterior adductor slender, circular in cross-section; gills extensive with both demibranchs, filaments homorhabdic; lips simple but broad, with extremely short palps with one marginal ridge; foot slender and elongate.

Remarks. This is the first species of Limea recorded from the Argentine Basin and is named after that country. It is characterized by a small number of ribs restricted to the central region of the shell and by the numerous fine teeth within scimitar-shaped hinge plates. The latter are stouter than those of L. sarsi . The species is somewhat reminiscent of Limea clandestina Salas, 1994 from the Mediterranean and which also has a limited number of central ribs, however, the latter species has a narrower shell and a very short hinge. The mantle margin is not particularly wide and the number of mantle tentacles/papillae is few. However, the features of the mantle margin may relate to the small size of the two specimens. Both specimens are immature. Because of the limited number of specimens no SEM photographs were taken.

Figures

FIG. 42. Limea argentinea. Sta. 237, lateral view of the right valve of the type specimen. Scale bar: 1 mm.

FIG. 43. Limea argentinea. Sta. 237, (a) internal view of left hinge; (b) dorsal view of right hinge. Scale bars: 1 mm.

FIG. 44. Limea argentinea. Sta. 237, (a) semi-diagrammatic view of the anatomy from the right side of a juvenile specimen; (b) ventral view of the lips of the specimen in figure 42. Scale bars: 1 mm.