Cubatea, Kiel & Campbell & Gaillard, 2010

Kiel, Steffen, Campbell, Kathleen A. & Gaillard, Christian, 2010, New and little known mollusks from ancient chemosynthetic environments, Zootaxa 2390 (1), pp. 26-48 : 40-41

Genus Cubatea gen. nov.

( Fig 9 )

Type species: Myrtaea (?) asphaltica Cooke, 1919 ; Oligocene?, from the Almira asphalt mine near Bejucal, Cuba, 22°.55’N 82°22’W (USGS locs. 3652 and 5312).

Diagnosis: Shell large (up to 57 mm), oval, umbo central, beaks prosogyrate; posterior margin well-rounded, area obsolete, ventral margin evenly rounded, anterior margin truncate; dense commarginal growth lines of equal strength on entire shell. Lunule heart-shaped, slightly wider in right valve, occupying approximately one third of distance between umbo and anterior shell margin; escutcheon narrow, lanceolate, bordered by sharp ridge. Hinge plate broad, cardinal in right valve strong, bifid, with the individual ends approximately perpendicular to each other, 3b absent; anterior lateral tooth strong, possibly bifid, posterior lateral tooth also strong, with shallow pit above; left valve with two strong cardinal teeth, bifid anterior and posterior lateral teeth. Ligament external, very large, deep and broad, resting on narrow nymph. Anterior adductor scar elongate teardrop-shaped, starting just below lateral tooth; ventrally detached from pallial line for about 2/3 of its length, diverging from pallial line about half its own width. No radial striations on interior shell surface; ventral margin smooth.

Remarks: The anterior adductor scars of the right valve figured here differ markedly from those figured by Cooke (1919, pl. 14, figs. 7a, b): Cooke showed one scar that is elongate-triangular, with the narrow angle pointing towards the interior of the shell. Cooke (1919: 149) considered this species closely related to Myrtea Turton, 1822 , but “very much larger than any hitherto described American species of that genus, and has weaker sculpture than is customary”. We agree on these differences but need to add that it lacks anterior elevated ribs and vermiculate radial ribs, and that it also differs from Myrtea by having a bifid cardinal tooth in the right valve, which is unusual for Myrtea and Myrteinae in general ( Chavan 1969).

Epilucina Dall, 1901 , has a similar hinge dentition, but differs from Cubatea by having a posterior area and a more slender anterior muscle adductor scar. Epilucina was considered a subgenus of the lucinid genus Codakia Scopoli, 1777 , by Chavan (1969) and as a subgenus of Miltha by Bretsky (1976). It was not available for the molecular phylogenetic study of Williams et al. (2004), but they considered Epilucina unrelated to Miltha based on shell characters. Miltha and Codakia have large ligaments similar to that of Cubatea ; Codakia differs from Cubatea by its reticulate sculpture. In contrast to Cubatea , Miltha shells are higher than long and have massive, spathulate, anterior adductor scars, and a distinct posterior ridge. A very similar hinge dentition as in Cubatea can also be seen in Parvilucina Dall, 1901 species described by Hickman (1994), but these Parvilucina species differ from Cubatea by being much smaller (<15 mm), having radial ribs, and a ribbed inner shell margin. The subgenus Miltha (Recticardo) resembles Cubatea regarding its hinge dentition, shape and surface ornamentation, but in Miltha (Recticardo) the projecting edge of the lunule is prolonged by ridge-like anterior lateral teeth ( Chavan 1969), a feature not seen in Cubatea . A nearly identical hinge dentition as Cubatea has Dilora lorea Marwick, 1948 , from the Pliocene of New Zealand. But the type of this monotypic genus is much smaller (<10 mm) than Cubatea asphaltica , and has fine radial ribblets and a nearly circular outline, unlike C. asphaltica . An additional difference to C. asphaltica is the more elongate and little diverging anterior adductor scar.

A similarly sized and shaped extant species from a presumed seep in the southern Caribbean is Graecina colombiensis Taylor & Glover 2009 . Cubatea asphaltica differs from that species by having a short, heart- shaped lunule rather than an elongate lunule, and by its strong cardinal tooth that points in a posteroventral direction, rather than anteroventrally, as in Graecina colombiensis ( Taylor and Glover 2009) . From seeps in 550 to 850 m depth on the Louisiana Slope (northern Gulf of Mexico) Taylor and Glover (2009) described the new lucinid genus Jorgenia , which is apparently related to Graecina , based on a species previously identified as Lucinoma sp. or Pseudomiltha sp. ( Turner 1985; García 2002). The species of Jorgenia are similar in outline and sculpture to Cubatea asphaltica , but, like Graecina , have a very elongate lunule unlike C. asphaltica , and are much less inflated than C. asphaltica .

Etymology: Combination of Cuba, where the species was found, and the ending –tea, from Myrtea , a morphologically similar lucinid genus.

Figures

FIGURE 9. The lucinid Cubatea asphaltica (Cooke, 1919) from the Almira asphalt mine in Bejucal, Cuba; A, B. Right valve (USNM 533988) showing details of hinge (images from Kiel and Peckmann, 2007). C-F. Original images of Cooke (1919) providing dorsal (C) and exterior (D, E) views, and details of the hinge of the left valve.