Pleurophopsis lithophagoides Olsson, 1931

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 : 116

publication ID	https://doi.org/ 10.4202/app.00631.2019
persistent identifier	https://treatment.plazi.org/id/F104879E-3B25-AD2B-F521-70CEFB64F92E
treatment provided by	Felipe
scientific name	Pleurophopsis lithophagoides Olsson, 1931
status

Treatment

Pleurophopsis lithophagoides Olsson, 1931 View in CoL

Fig. 6 View Fig .

1931 Pleurophopsis lithophagoides View in CoL sp. nov.; Olsson 1931: 44, pl. 4: 2, 5, 7, 9.

Material.— Five specimens ( NRM Mo187014–187018) and 63 unnumbered, often fragmentary specimens from the Belén seep site, upper Oligocene, Talara Basin, Peru .

Description.—Shell narrow (W/H ratio 0.58–0.66 of the six measured shells), elongate-oval shell (H/L ratio 0.52–0.45 of the five smallest [L = 22–27 mm] specimens, 0.33–0.40 of the five largest [L = 32–40 mm] specimens), umbones slightly elevated, prosogyrate, pointed, positioned anterior at c. 20% total shell length; anterior margin short, convex; posterodorsal margin gently sloping to acutely rounded posterior margin; ventral margin straight or slightly convex; sculpture of irregular growth increments only. Anterior adductor muscle scar kidney-shaped, somewhat impressed; anterior pedal retractor scars small, roundish and connected to adductor scar by fine groove. Narrow sinuous hinge plate; RV with two cardinals, 1 pointing anterior, 3b pointing slightly posterior; LV with three cardinals, 2a pointing antero-ventral, 2b pointing slightly posterior, 4b seen as elongated socket pointing posterior.

Remarks.—All specimens are fragmentary, and the full extent of the hinge plate is unknown. The details on the dentition given here are derived from silicon rubber casts of parts of the hinge and observations on internal molds ( Fig. 6E View Fig ). Pleurophopsis lithophagoides differs from the type species P. unioides by reaching a smaller maximum size (up to 40 mm in length compared to 77 mm for P. unioides ) and by being more elongated. The Peruvian Pleurophopsis talarensis sp. nov. described below differs from P. unioides mainly by being much more elongated (H/L ratio 0.26 compared to 0.33–0.4 in large P. lithophagoides ). Differences to other species of Pleurophopsis are summarized in Table 1.

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