Aksumya, Kiel, 2018

Kiel, Steffen, 2018, Three new bivalve genera from Triassic hydrocarbon seep deposits in southern Turkey, Acta Palaeontologica Polonica 63 (2), pp. 221-234 : 226-229

Genus Aksumya nov.

Etymology: Combined from the town Aksu near the type locality, and the bivalve genus Mya .

Type species: Aksumya krystyni sp. nov; see below.

Species included: The type species and possibly also the “nuculanid”

from a Norian, Late Triassic seep deposit in Oregon ( Peckmann et al. 2011).

Diagnosis.—Shell nuculaniform with elongated, tapering posterior side, broad umbonal sulcus and sinuous ventral margin, surface sculpture of commarginal growth lines and fine pustules; hinge plate with two blunt teeth in each valve and a short and strong ligament nymph holding an calcified external ligament; shell interior with radial striation; anterior adductor muscle scar roundish to quadrate, fused dorsally with anterior pedal retractor scar; pallial line entire and close to ventral margin, no pallial sinus.

Remarks.—Regarding its overall shell shape, muscle scar and hinge characters, and the fine pustules on the shell surface, Aksumya can safely be placed among the Pholadomyoidea . But assigning it to any of the currently recognized families is rather difficult. With some Paleozoic Grammysiidae = Sanguinulitidae) it shares the broad umbonal sulcus and sinuous ventral margin, and possibly its hinge dentition (i.e., Tellinomorpha , cf. Morris and Dickins 1991). However, similar shell shapes are also found among the Mesozoic–Recent

Pholadomyidae ( Pachymya , Machomya ), and the hinge features shown here on polished surfaces and interpreted as teeth also resemble the pits for internal ligaments documented for Pholadomya ( Newell 1969) .

from the posterior margin than Aksumya . Machomya de Loriol in de Loriol and Cotteau, 1868 has an anterior internal rib, whereas Aksumya has such a rib on the posterior side. Externally, shells of Homomya Agassiz, 1843 and of Pleuromya Agassiz, 1842 are quite similar, but both genera have a deep pallial sinus, which Aksumya lacks.