Limatula confusa ( Smith, 1885 )

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 : 52

Limatula confusa ( Smith, 1885)

Figures 6–9

Lima confusa Smith, 1885: p. 292 , pl. XXIV, fig. 6, 6a.

Limatula confusa: Stuardo, 1968 : pl. 16, fig. 88; Abbott, 1974: p. 454.

Description: Shell fragile, white, small (height mean = 3.28mm ± 2.06 s.d.; range 1.10–6.30mm; n=14), height/length ratio 1.41, equivalve, slightly unequilateral, very inflated, outline suboval, thin axial ribs cover entire shell, but axial ribs not evenly spaced. The axials are closer to each other on the dorsal side, and slowly increase in the distance between them towards the ventral side, very fine concentric striae present, forming small nodules where they cross the axial ribs. Internal axial ridge absent. Auricles small, with few ornaments, subauricular sinus present, ventral region rounded or angled. Prodissoconch smooth (mean 177.50µm ± 16.69 s.d.; range 160–200 µm; n=14), interdissoconch hardly distinguishable in some specimens (mean 805.00µm ± 33.38 s.d.; range 760–860 µm; n=14). Umbones prominent, hinge plate large, ligamental pit broad, triangular.

Geographic range: North Carolina to the West Indies, off Azores, Northeast Brasil, off Pernambuco State. Depths ranging between 60 to 2650 meters. Adapted from Abbott (1974), Rios (1994) and Allen (2004). Campos Basin (this study), is the southernmost record in the Atlantic Ocean.

Material examined: IBUFRJ 17802, off Bacia de Campos (21°57'27" S, 39°40'34" W, 1942 m), 27. VI.03, [1 valve]; IBUFRJ 17803, off Bacia de Campos (21°52'41" S, 39°46'17" W, 1688 m), 26. VI.03, [1 valve]; IBUFRJ 17804, off Bacia de Campos (22°11'17" S, 39°43'45" W, 1950 m), 25.XI.02, [1 valve]; IBU- FRJ 17807, off Bacia de Campos (21°58'36" S, 39°46'30" W, 1700 m), 10. VIII.01, [1 valve]; IBUFRJ 17812, off Bacia de Campos (22°31'37" S, 39°55'14" W, 1630 m), 16. VI.03, [1 valve]; IBUFRJ 17813, off Bacia de Campos (22° 24'32" S, 39°57'28" W, 1050 m), 20.XI.02, [1 valve]; IBUFRJ 17814, off Bacia de Campos (22°36'12" S, 39°58'23" W, 1670 m), 13. VI.03, [1 valve]; IBUFRJ 17815, off Bacia de Campos (22°31'28" S, 40°03'50" W, 1043 m), 18. VI.03, [1 valve]; IBUFRJ 17816, off Bacia de Campos (21°57'27" S, 39°40'34" W, 1942 m), 27. VI.03, [1 valve]; IBUFRJ 17817, off Bacia de Campos (22°04'45" S, 39°46'32" W, 1643 m), 27. VI.03, [1 valve]; IBUFRJ 17818, off Bacia de Campos (22°11'04" S, 39°47'05" W, 1650 m), 25.XI.02, [1 valve]; IBUFRJ 17819, off Bacia de Campos (22°10'54" S, 39°52'19" W, 1050 m), 10. XII.02, [1 valve]; IBU- FRJ 17820, off Bacia de Campos (22°05'45" S, 39°45'55" W, 1730 m), 09. V.02, [1 valve]; IBUFRJ 17821, off Bacia de Campos (22°05'04" S, 39°50'02" W, 1230 m), 09. V.02, [1 valve]; IBUFRJ 17822, off Bacia de Campos (22°39'34" S, 40°08'22" W, 1200 m), 15. V.02, [1 valve] .

Remarks: Apparently this species has not been collected since its description (from the Challenger Expedition material), and a part of the type series was destroyed ( Allen 2004, p. 2644). However, the description and especially the type illustration in plate 24, figs. 6-6a ( Smith 1885 p. 292), are good enough to allow us to identify it. In our description we include details that were not mentioned in the original description because of the limitations in optics of the period.

Limatula margaretae Allen, 2004 is the most similar taxon to L. confusa in the Atlantic basin: both species share the same outline and type of ornamentation, but can be distinguished by the presence of axial ribs over all the shell including the auricles in L. confusa (fig. 6–7), while the auricles are devoid of axial ribs and the central and postero-central axial ribs are barely visible in L. margaretae . Besides that, the umbones at L. margaretae are more prominent than in L. confusa .