Kalenteridae Marwick, 1953

Kiel, Steffen, Hybertsen, Frida, Hyžný, Matúš & Klompmaker, Adiël A., 2020, Mollusks and a crustacean from early Oligocene methane-seep deposits in the Talara Basin, northern Peru, Acta Palaeontologica Polonica 65 (1), pp. 109-138 : 112-114

Family Kalenteridae Marwick, 1953 Genus Pseudophopsis nov.

Zoobank LCID: urn:lsid:zoobank.org:act:9FF851DC-2A55-4CC0-888D-6E91D0042CB1

Type species: Pleurophopsis peruviana Olsson, 1931 ; Oligocene , Peru .

Species included: The type species and Unio bitumen Cooke, 1919 .

Etymology: For its superficial similarity to the vesicomyid genus Pleurophopsis .

Diagnosis.—Medium-sized, well-inflated, elongate-oval kalenterid with blunt, somewhat elevated umbo in anterior third of shell; external sculpture rough, irregular; hinge plate strong, moderately narrow, with indistinct growth lines, hinge teeth weak, sub-parallel to shell margin, often reduced in adults; anterior adductor muscle scar deep, roundish, with peg in upper half of posterior margin; anterior retractor muscle scar large, roundish, above ridge bordering adductor muscle scar; onset of pallial line at posteroventral side of anterior adductor muscle scar, no pallial sinus; ligament external, long, strong.

Remarks.— Van Winkle (1919) derived the generic name Pleurophopsis from the Paleozoic “modiomorphid” genus Pleurophorus King, 1848 (a synonym of the beetle genus Pleurophorus Mulsant, 1842 and hence replaced by Permophorus Chavan, 1954 ) because she considered Pleurophopsis to be a descendent of Pleurophorus based on the hinge structure and muscle scar pattern. Olsson (1931) adopted this classification when introducing Pleurophopsis peruviana , and placed Pleurophopsis in the Permophoridae . It is now firmly established that the type species of Pleurophopsis , P. unioides (see below), belongs to the Vesicomyidae (Kiel 2007; Krylova et al. 2010; Krylova and Sahling 2010). However, Olsson’s (1931) “ Pleurophopsis ” peruviana does indeed show “modiomorphid” hinge and muscle scar features and hence the new genus Pseudophopsis , with P. peruviana as the type species, is here placed among the Kalenteridae .

In contrast to vesicomyids, Pseudophopsis peruviana has a relatively large anterior pedal retractor scar that is clearly separated from the adductor muscle scar. The entire anterior adductor muscle scar is sunken, whereas in vesicomyids it is usually deepest on its posterior side and shallower impressed on the anterior side. Another distinguishing feature is the hinge plate, which is set distinctly inward from the umbones, whereas is situated directly underneath the umbones in vesicomyids (or in other words, the umbones are more loosely coiled than in vesicomyids). Such a distinctive hinge plate is for example seen in the kalenterid Myoconcha neuquena Leanza, 1940 from the Early Jurassic of Argentina ( Leanza 1940; Griffin and Pastorino 2006). Similar fine growth lines on the hinge plate of P. peruviana ( Fig. 3G 1 ) can be seen in Myoconcha neuquena showing posterior half of pallial line (B 1, B 3) and thick ligament (B 2). C, D. Inner sides of two fragmentary right valves preserving anterior margin (C, USNM PAL 728209; D, USNM PAL 530294), showing anterior adductor muscle scar and pedal retractor scar, and onset of pallial line. E. Fragment ( NRM Mo187027) preserving anterior half of shell and thick calcified ligament; outer side of right valve (E 1) and dorsal view (E 2). F. Fragment ( NRM Mo187028) preserving edentulous hinge area (F 1) and large anterior pedal retractor scar (F 2). G. Dorsal shell margin of large left valve ( USNM PAL 530295), showing edentulous hinge (G 1, close-up). D and G from Kiel and Peckmann (2007: fig. 6).

and also in the Miocene kalenterid Madrynomya bruneti Griffin and Pastorino, 2006 . Madrynomya is clearly distinct from Pseudophopsis by its more coiled and more pointed umbones, and the much broader but shorter hinge plate. Myoconcha Sowerby, 1824 , differs from Pseudophopsis by its bean-shaped posterior adductor muscle scar, and the anterior side of the pallial line, which is distinct from the anterior adductor muscle scar in Myoconcha , but starts at its posteroventral corner in Pseudophopsis (i.e., Leanza 1940; Newell 1957; Griffin and Pastorino 2006; Kaim and Schneider 2012). Lastly, Pseudophopsis peruviana has a coarser and much more irregular surface sculpture than any vesicomyid, and also its ligament is longer relative to shell length as in vesicomyids.

The late Mesozoic, seep-inhabiting kalenterid Caspiconcha Kelly in Kelly et al., 2000, typically has an elongated anterior adductor muscle scar with a posterodorsal projection, which is absent in Pseudophopsis , a more distinctive projection above the anterior adductor muscle scar (the socalled caspiconchid process) not seen in Pseudophopsis , and it lacks hinge dentition ( Kelly et al. 2000; Kiel et al. 2010; Jenkins et al. 2013, 2018b). Further, several but not all species of Caspiconcha have an internal ridge running from the umbo to the posterior adductor scar, which is not seen in P. peruviana , and the pallial line tends to be closer to the ventral shell margin in Pseudophopsis than in Caspiconcha see Jenkins et al. 2018b: fig. 2).

Another species included here in Pseudophopsis is the Eocene Unio bitumen Cooke, 1919 , from the Elmira asphalt mine seep deposit in Cuba ( Cooke 1919; Kiel and Peckmann 2007; Kiel and Hansen 2015). Pseudophopsis bitumen resembles P. peruviana by having a similar inward-set hinge plate with similarly reduced teeth, its thick ligament and very rough and irregular surface.

Stratigraphic and geographic range.—Early Oligocene of the Talara Basin, northern Peru and Eocene of Cuba.

Figures

Fig. 1. Locality map of the seep deposits in the Talara Basin in northern Peru, where the here described mollusk and crustacean taxa were found adopted from Kiel et al. 2019).