Limatula domaneschii, Oliveira & Absalão, 2008

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 : 52-53

Limatula domaneschii n.sp.

Figures 10–12

Description: Shell fragile, white, small (height mean = 1.07mm ± 0.15 s.d.; range 0.90–1.20mm; n=3), height/length ratio 1.43, slightly inequilateral, moderately inflated, outline suboval, ornamented with rela- tively equidistant thin concentric ridges that become more apparent toward the ventral margin. Dorso-central region without ornamentation. Secondary faint ridges may be present between the primary ridges. The concentric ridges extend toward the auricles, which become furrowed. With no external or internal axial ornamentation. Auricles small, symmetrical, and slightly inclined in relation to the antero-posterior axis, dorsal edge raising upwards slightly, subauricular sinus absent, posterior margin slightly more curved than the anterior margin. Ventral margin evenly curved. Prodissoconch smooth and rounded in shape, with conspicuous edge (mean 170.00µm ± 5.00 s.d.; range 165–175 µm; n=3). Interdissoconch not distinguishable. Umbones prominent. Hinge plate large, without teeth. Ligamental pit rounded.

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

Material examined: Holotype: IBUFRJ 17806, off Bacia de Campos (22°24'30" S, 39°57'29" W, 1044 m), 20. VI.03, [2 valves]; paratype 1-IBUFRJ 17801, off Bacia de Campos (22°24'30" S, 39°57'29" W, 1044 m), 20. VI.03, [2 valves].

Etymology: This species is named in honor of Dr. Osmar Domaneschi, a Brazilian malacologist, for his contribution to the knowledge of functional anatomy of the pelecypods and his contribution to the SBMa (Sociedade Brasileira de Malacologia, Brazilian Malacological Society) for which he served more than 10 years as vice president.

Remarks: Because of the similarities among the genera of Limidae , we chose to compare our proposed new taxon with all the species that are characterized mainly by the presence of concentric ornamentation, regardless of their present generic allocation.

Limea lirata Allen, 2004 is more oblique and somewhat more rounded than L. domaneschii n.sp. Moreover, L. lirata is ornamented with numerous concentric lines, which are closer to each other and cover the entire shell; the umbones are more slender and comparatively more projected beyond the hinge than the umbones of L. domaneschii n.sp. The main difference is the very fine axial ridges in L. lirata , which are absent in L. domaneschii n.sp.

Limatula domaneschii n.sp. can be distinguished from L. laminifera ( Smith, 1885) by the presence, in the latter, of an elongated, triangular ligamental pit, ornamentation over the entire shell, the presence of an auricular sinus, a slender umbo, and a short hinge plate; whereas L. domaneschii n.sp. has a rounded ligamental pit, the dorso-central region without ornamentation, no auricular sinus, and a comparatively large umbo and hinge plate. Also, L. laminifera bears, internally, two thickened axial ridges at the middle of the shell, and axially oriented slender striae, but both characters are absent in L. domaneschii n.sp. Additionally, L. domaneschii n.sp. has the dorsal edge raising upwards slightly, which does not occur in any other species known from the Brazilian coast and the surrounding area.

Limatula louiseae and L. domaneschii n.sp. share the concentric ornamentation, but the former species shows the diagnostic microscopic diagonal striae that are absent in L. domaneschii n.sp.. Besides that, L. louiseae is slender (height/length ratio 1.53), its prodissoconch is small (109µm) and the ligamental pit is triangular, whereas L. domaneschii n.sp, has a height/length ratio of 1.43, a prodissoconch of 170 µm and a rounded ligamental pit.

A comparison with the 87 Limatula presumed species in Stuardo (1968) showed no close similarity with L. domaneschii n.sp.; most of them have dominant axial ornamentation while L. domaneschii n.sp has exclusively concentric ornamentation.