Limea sarsi Loven 1846

Limea sarsi Lovén, 1846

(figures 38–41, 46d)

Type locality. ?Varanger Fjord, Norway.

Syntypes. Six v, SMNH No. 2003.

Material examined. Thalassa sta. Z397, 47 ‡ 33.8 ’ N, 07 ‡ 12.6 ’ W, 511 m, 9 spec.; sta. Z399, 47 ‡ 34.8 ’ N, 07 ‡ 18.1 ’ W, 825 m, 3 spec.; sta. Z402, 47 ‡ 39.5 ’ N, 07 ‡ 28.5 ’ W, 450 m, 2 spec.; sta. Z414, 48 ‡ 05.0 ’ N, 08 ‡ 29.8 ’ W, 650 m, 1 spec.; sta. Z420, 48 ‡ 19.8 ’ N, 09 ‡ 37.8 ’ W, 507 m, 1 spec.; sta. Z431, 48 ‡ 38.2 ’ N, 09 ‡ 47.3 ’ W, 800 m, 3 spec.

Distribution. Upper slope depths in the north-eastern Atlantic, from Veranger Fjord in northern Norway south to off south-west Ireland. It is supposedly reported further south from off St Helena and from the Mediterranean though these records are almost certainly of the closely related species Limea crassa (see Appendix). Depth range: ca 100– 825 m.

Redescription (figures 38, 39, 46d). Shell small (max. recorded height 5.5 mm), height/length ratio 1:0.72, ovate, moderately robust, moderately inflated, equivalve, subequilateral, white, ornamented with 24–27 broad radial ribs extending some distance ventral to umbo in contrast to regular concentric lamellate ridges which extend over entire shell, ventral concentric ridges wavy which crest on ribs producing crenulations, nine central ribs much stronger than those lateral to them, lateral radial ribs grade to being barely discernible; interdissoconch with dorsal-most concentric ridges; ears of shell small without ribs, subauricular sinuses not particularly obvious; umbos prominent; dorsal margin of hinge elongate, straight at oblique angle to central vertical axis of shell; hinge plate narrow with ca 10 short, weak, vertical, teeth, central region without teeth, resilifer elongate, lozenge-shaped with central triangular ligament. Prodissoconch I length~390 M m; interdissoconch ca 1.5 mm.

Anatomy (figures 40, 41). Mantle margins extremely broad, in preserved specimens extend over half mantle cavity space, composed largely of middle sensory layer, each bears numerous tentacles and papillae and one large anal tentacle close to postero-dorsal margin, fine connective attachments extend from base of anal tentacle to the dorsal mantle margin, seven large tentacles occur posteroventrally and ventrally in centre of sensory fold, ca 13 smaller tentacles lie closer to margin and interspace with latter along anterior margin, ca 12 small peripheral papillae further interspace with latter; gills very large, inner and outer demibranchs reflected with large numbers of homorhabdic filaments extending into space between extended mantle margin and the mantle epithelium lining of the shell, gills not modified to contain developing eggs; palps small, lips simple; posterior adductor muscle relatively large, oval in cross-section; foot in preserved specimens relatively small; dioecious, gonads when ripe extend over visceral mass, eggs ca 150 M m.

Remarks. Limea sarsi frequently has been synonymized with L. crassa (see Appendix). That they are very similar is without doubt. However, close inspection shows that L. sarsi has a much straighter and longer dorsal hinge margin, less marked posterior subauricular sinus, radial ribs less regular and less extensive than those of L. crassa and with a much larger interdissoconch with concentric ridges without radials superimposed. These differences can be clearly seen when figure 29 of Tebble (1966) (which although labelled L. sarsi is a Mediterranean specimen of L. crassa) is compared with figures 38 and 46 (d) of the present paper.