Tehamatea Kiel, 2013

Hryniewicz, Krzysztof, Little, Crispin T. S. & Nakrem, Hans Arne, 2014, Bivalves from the latest Jurassic-earliest Cretaceous hydrocarbon seep carbonates from central Spitsbergen, Svalbard, Zootaxa 3859 (1), pp. 1-66 : 30-31

Genus Tehamatea Kiel, 2013

Type species. Lucina ovalis Stanton, 1895

Remarks. We assign our lucinid specimens to the genus Tehamatea Kiel, 2013 , based on their external ornament composed of commarginal growth lines only, oval external shape of the shell, reduced 3a cardinal, and the length and divergence angle of the anterior adductor muscle scar (Kiel 2013). Tehamatea is a Late Jurassic–Early Cretaceous seep-restricted genus known from California ( Stanton 1895), the Basque-Cantabrian Basin ( Agirrezabala et al. 2013), the Vocontian Basin and Planerskoje in Crimea ( Kiel & Peckmann 2008; Kiel 2013). The similar lucinid genus Beauvoisina Kiel, Campbell & Gaillard, 2010 , has much weaker muscle scars than the Svalbard specimens, and has a ridge developed within the lunule, a feature not seen in our material ( Kiel et al. 2010; Kiel 2013). Beauvoisina also has beaks located further towards the posterior than the Svalbard specimens. Another seep-restricted lucinid genus, Cubatea Kiel, Campbell & Gaillard, 2010 , differs from our specimens by having a much stronger anterior lateral teeth and lacking a 3b cardinal. The Late Cretaceous–Paleocene seep lucinid genus Nymphalucina Speden, 1970 , has an external ornament composed of sparse commarginal ridges, stronger sulcation, and strong cardinal and lateral dentition ( Speden 1970; Kiel 2013), all features lacking in our material. Comparable Mesozoic non-seep lucinid genera include Jagonoma Chavan, 1946 , from the Jurassic of France ( Chavan 1946; 1947; 1952), but our specimens do not belong to this genus because it has stout cardinal dentition, with thick and well-formed 3a and 3b, and an anterior adductor muscle scar that only weakly diverges from the pallial line. Another European Jurassic genus, Discomiltha Chavan, 1952 , is on average less inflated than the Svalbard specimens, has an external ornament composed of regularly spaced, commarginal ridges and cardinal dentition of two weak denticles (e.g. Duff 1978). The Jurassic genus Mesomiltha Chavan, 1938 , differs from our specimens with its regular commarginal ornament and more angular shape (e.g. Kelly 1992). Discoloripes Wellnhofer, 1964 , has a similar shape to the Svalbard material, but has a much longer and club-shaped anterior adductor muscle scar (e.g. Wellnhofer 1964; Kelly 1992).

The taxonomy of Mesozoic lucinids is currently problematic, and in need of revision, because many Mesozoic and Recent species are homeomorphic and difficult to distinguish without in-depth study (e.g. Gerasimov 1955; Wellnhofer 1964; Kelly 1992). Further, many Mesozoic lucinids have been classified tentatively as “ Lucina ” (e.g. Woods 1907, p. 152–153, fig. 2–6, 10–19; Lewinski 1922, p. 78, pl. 4, fig. 4). Recent molecular phylogenetic studies show that most of the modern lucinid lineages can be traced back through the Cenozoic, but are much more difficult to recognize in the Mesozoic ( Williams et al. 2004; Taylor et al. 2011).