Terzileria, 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 : 222-224

Genus Terzileria nov.

Etymology: For the village of Terziler, near the type locality.

Type species: Terzileria gregaria sp. nov.; see below.

Species included: The type species and possibly also the “permophorid” reported from a Norian , Late Triassic seep deposit in eastern Oregon, USA ( Peckmann et al. 2011) .

Diagnosis.—Modioliform shell, subterminal umbones, elongate-lenticular escutcheon, shell surface with growth lines and faint posterodorsal groove; hinge plate edentulous, ligament nymph short and close to shell margin, elongate posterior lateral tooth quite distinct in left valve but less so in right valve; anterior adductor muscle scar deep, oval to almost round, positioned at anterior end of shell; anterior pedal retractor scar not fused with adductor muscle scar; pallial line entire and running close to ventral shell margin, no sinus; posterior adductor muscle scar round with projection (probably fused posterior pedal retractor scar) on anteroventral side.

Remarks.—Most similar to Terzileria is the Permian Netschajewia Likharev, 1925 , with its modioliform outline, edentulous hinge plate, and the elongate posterior lateral tooth being stronger in the left valve. Terzileria differs from Netschajewia by having an elongate-lenticular escutcheon (lacking in Netschajewia ) and a more-or-less evenly convex globosity of the shell, whereas Netschajewia has a distinct broad ridge running from the umbo to the posteroventral margin ( Murchison et al. 1845). The available descriptions and illustrations of the type species of Netschajewia (i.e., Pleurophorus modioliformis King in de Verneuil and Murchison, 1844 = Mytilus pallasi de Verneuil in Murchison et al., 1845) did not discuss or show the anterior pedal retractor muscle scar, the posterior adductor muscle scar and the possible presence of a pallial sinus ( Murchison et al. 1845; King 1850; Newell 1957; Chavan 1969).

Also very similar to Terzileria is the Jurassic–Cretaceous seep-restricted genus Caspiconcha Kelly in Kelly et al. 2000. They differ by the following features: (i) in Caspiconcha the anterior adductor muscle scar is in a more dorsal position than in Terzileria ; (ii) in Caspiconcha the anterior adductor muscle scar and the pedal retractor scar are fused, whereas in Terzileria they are separated; (iii) in Terzileria the pallial line is closer to the shell margin than in Caspiconcha ;

Fig. 2. The kalenterid bivalve Terzileria gregaria gen. et sp. nov. from the late Carnian, Late Triassic Terziler III seep deposit in southern Turkey. → A. Mo184051, holotype, internal mold, left valve (A 1), dorsal (A 2) and anterior (A 3) views. B. Mo 184052, paratype, specimen with shell partially preserved, left valve (B 1), dorsal (B 2) and anterior (B 3) views. C. Mo 184053, paratype, small specimen with shell preserved on most of posterior side, left valve (C 1), the same at slightly different angle (C 2), dorsal view (C 3). D. Mo 184054, fragmentary but articulated specimen, interior of the dorsal side, showing the edentulous hinge. E. Mo 184055, paratype, large specimen showing outer shell surface of the anterior half of the shell; left valve (E 1) and dorsal view (E 2) .

iv) secondary pallial attachment scars tend to be found in the anterior half of the shell in Caspiconcha , whereas in Terzileria they tend to occur more posteriorly ( Kelly et al. 2000; Kiel et al. 2010; Jenkins et al. 2013, 2018).

The type species of Kalentera Marwick, 1953 is similar in shell outline, the lateral tooth in the left valve and the shape of the anterior adductor muscle scar ( Marwick 1953; Chavan 1969) but is clearly distinct from Terzileria by having cardinal teeth. Other species of Kalentera are more trapezoidal in outline and have a distinctive angular ridge running from umbo to the posteroventral corner (GrantMackie 1979; Covacevich et al. 1991; Damborenea 2004).

The genus Healeya Hautmann, 2001 has a similarly shaped pallial line, anterior adductor muscle scars and a separated pedal retractor scars, but clearly differs from Terzileria by its strong and sharp diagonal keel running from the umbo to the posteroventral margin, and by its thicker hinge plate ( Hautmann 2001). Similar to Terzileria regarding modioliform shell and subterminal umbo is the Late Triassic Myoconcha ( Pseudomyoconcha ?) auriculata Broili, 1903 as figured in Hautmann (2001), but it differs from Terzileria by having fine radial ribs on the shell surface. Myoconcha Sowerby, 1824 has a narrower and more pointed anterior margin than Terzileria , and possesses cardinal teeth, whereas Terzileria is edentulous ( Chavan 1969). The Late Triassic Ouamouia grantmackie Campbell, 1984 from New Caledonia and New Zealand is more bean-shaped than Terzileria (by having a broader anterior margin and a less wide posterior margin), has a much stronger hinge plate that features cardinal teeth, a smaller anterior adductor muscle scar, and fine radial striation on the anteroventral shell surface ( Campbell 1984). The type species of Triaphorus Marwick, 1953 , Triaphorus zealandicus ( Trechmann, 1917) , also has a broader anterior margin and a narrower posterior margin compared to Terzileria , and possesses cardinal teeth ( Chavan 1969; Damborenea 2004). Most other kalenterid genera differ from Terzileria by possessing cardinal teeth (i.e., Permophorus , Celtoides , Pseudopermophorus , Curionia , Myoconcha , and Pseudomyoconcha ; see Chavan 1969).

The new genus Kazimlara described below from the same seep deposits differs by being much more inflated, having a much smaller anterior adductor muscle scar, and by showing a lateral curvature of the shell that is not seen in Terzileria .