Vesicomya Dall, 1886

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 : 117-119

publication ID	https://doi.org/ 10.4202/app.00631.2019
persistent identifier	https://treatment.plazi.org/id/F104879E-3B2A-AD26-F61D-71C5FB3EFA47
treatment provided by	Felipe
scientific name	Vesicomya Dall, 1886
status

Treatment

Genus Vesicomya Dall, 1886 View in CoL

Type species: Callocardia atlantica Smith, 1885 , by original designation; Recent , North Atlantic Ocean .

“ Vesicomya ” tschudi Olsson, 1931 View in CoL

Fig. 8 View Fig .

1931 Vesicomya tschudi View in CoL sp. nov.; Olsson 1931: 54, pl. 4: 6, 8.

Material.—One small, articulated specimen ( NRM Mo 187029) from Cerro La Salina block 1; one medium-sized, articulated specimen ( NRM Mo187030) from Cerro La Salina block 5; one large LV ( NRM Mo187031) from Cerro La Salina block 5. All upper Oligocene, Talara Basin, Peru.

Dimensions (in mm).— NRM Mo187029, L = 20, H = 14, W = 10.5; NRM Mo187030, L = 41.5, H = 27, W = 19.5; NRM Mo187031, L = 59, H = 37.5, W (single valve) = 14.

Description.—Well-inflated, oval shell with large, prosogyrate and strongly protruding umbones; post-umbonal side of shell gently tapering into a slightly truncate posterior margin; lunular incision present, no escutcheon, but posterodorsal area marked by distinct ridge; external sculpture of indistinct, irregular, commarginal growth lines; anterior adductor muscle scar bean-shaped, small, and moderately impressed; posterior adductor scar indistinct, round, of moderate size; pallial line close to ventral margin, no pallial sinus.

Remarks.—Along with Vesicomya tschudi, Olsson (1931) also introduced Vesicomya ramondi Olsson, 1931 , from the Heath shale around Belén and Pajarabobo, but he did not comment on the differences between the two species. Squires and Gring (1996) noted that V. ramondi has a more elongated shell, as can be seen when comparing the holotypes of the two species (see Fig. 8C, D View Fig ). Squires and Gring (1996) assigned Eocene specimens from seep deposits of the Wagonwheel Formation in California, USA, to V. tschudi , based on their overall shape, although the specimens showed no hinge dentition, the lunule was imperfectly preserved, and most specimens were smaller and had lower umbones than the Peruvian specimens.

Middle Eocene vesicomyid specimens from the Humptulips Formation in Washington state, USA, were identified as Archivesica cf. tschudi by Amano and Kiel (2007). Later, the same authors changed their assignment of these specimens from Archivesica to Pliocardia or a new genus ( Amano and Kiel 2012). The middle Miocene Pliocardia? tanakai Miyajima, Nobuhara, and Koike, 2017 , from central Japan ( Miyajima et al. 2017) is similar to “ V.” ramondi in terms of its outline, elongation, and absence of a pallial sinus, but is smaller, less inflated, and has smaller, more pointed, and less prosogyrate umbones than “ V.” ramondi . Pliocardia? tanakai is much smaller and also more elongated than “ Vesicomya ” tschudi .

“ Vesicomya ” tschudi View in CoL cannot be confidently placed in Pliocardia View in CoL because it lacks a pallial sinus, a feature that is present in the type species of Pliocardia View in CoL , P. bowdeniana Dall, 1903 View in CoL ( Krylova and Janssen 2006; personal observation SK). The presence or absence of a pallial sinus appears to be a character that distinguishes genera among the Vesicomyidae ( Johnson et al. 2017) View in CoL . Furthermore, the genus Pliocardia Woodring, 1925 View in CoL itself is in need of a taxonomic revision because the species presently assigned to it belong to at least two or three different clades ( Decker et al. 2012; Valdés et al. 2013; Johnson et al. 2017). Hence the generic position of “ Vesicomya ” tschudi View in CoL remains unresolved.