Squiresica Hybertsen, Goedert, and Kiel, 2022

Kiel, Steffen, Amano, Kazutaka & Goedert, James L., 2023, New taxa, records, and data for vesicomyid bivalves from Cenozoic strata of the North Pacific region, Acta Palaeontologica Polonica 68 (2), pp. 297-320 : 307

Genus Squiresica Hybertsen, Goedert, and Kiel, 2022

Type species: Archivesica knapptonensis Amano and Kiel, 2007 , by original designation; Oligocene, western Washington State, USA ( Hybertsen et al. 2022).

Remarks.—Some species of Squiresica show a dimorphism in shell shape. The posterior part of the shell either has an evenly rounded posterior margin (i.e., S. yooni sp. nov., Fig. 9C 2 ) or a sloping posterodorsal margin (i.e., S. yooni sp. nov., Fig. 9A 3 , B 2 ). This dimorphism has been reported from extant vesicomyid taxa such as Calyptogena ( Krylova and Sahling 2006) . Although it occurs in fossil vesicomyids too (SK personal observation), it is rarely explicitly described.

Figures

Fig. 9. The vesicomyid bivalve Squiresica yooni sp. nov., from the Middle Miocene Duho Formation, loc. 18 of Yoon (1976b), South Korea. A. Holotype, NRM Mo 204829, an articulated specimen with preserved cast of RV hinge area; close-up on hinge area (A1), view on right valve and exposed hinge of left valve (A2), and view on left valve (A3). B. Paratype, NRM Mo 204832, articulated specimen, mostly an internal mold; dorsal view showing inflation (B1); view on exterior of RV (B2); close-up on anterior part of LV showing the lack of a lunular incision (B3). C. Paratype, NRM Mo 204831, articulated specimen with some shell preserved; dorsal view showing inflation (C1); lateral view on RV showing fine growth increments (C2).

Fig. 2. The small vesicomyid bivalves Vesicomya? sp. 1 and sp. 2, from Oligocene seep deposits in the Lincoln Creek Formation, western Washington State, USA. A. Vesicomya? sp. 1 from the early Oligocene SR2 site, Satsop River. NRM Mo 204811, left side view (A1) and dorsal view on LV and dorsal side of actual specimen (A2); A3, A4, X-ray section through the hinge area, with our interpretations; A5–A7, 3D renderings of the specimen. B, C. Vesicomya? sp. 2 from the late Oligocene SR4 site, Satsop River. B. NRM Mo 204701, disarticulated specimen, view on RV with naticid drill hole on the umbo (B1) and on the LV showing the truncate posterior margin (B2). C. NRM Mo 204702, RV in anterior view, showing inflation and lunular incision (C1) and dorsal view, showing lunular incision (C2).

Fig. 3. The vesicomyid bivalve Isorropodon humptulipsense sp. nov., from middle to upper Eocene strata in western Washington State, USA. A. Rubber cast of the paratype, NRM Mo 204722, Humptulips Formation, CSUN loc. 1583, hinge area, RV (A1), LV (A2). B. Holotype, NRM Mo 204723, Humptulips Formation, CSUN loc. 1583, internal mold, view on LV.C. NRM Mo 204724, Humptulips Formation, LACMIP loc. 12385, articulated specimen, view on anterodorsal margin showing lunular incision. D. Paratype, NRM Mo 204733, Humptulips Formation, near East Fork Bridge site, view on anterodorsal margin and anterior adductor muscle scars. E. Paratype, NRM Mo 204744, Siltstone Unit B along Grays River, specimen with partially preserved shell. F. Paratype, NRM Mo 204743, Siltstone Unit B along Grays River, internal mold showing pallial line with slight indentation on RV. G. Internal mold, USNM 534952, Humptulips Formation, CSUN loc. 1583, view on RV with pallial line curving evenly into posterior adductor muscle scar (re-illustrated from Amano and Kiel 2007).