Archivesica, Dall, 1908

Kiel, Steffen, Fernando, Allan Gil S., Magtoto, Clarence Y. & Kase, Tomoki, 2022, Mollusks from Miocene hydrocarbon-seep deposits in the Ilocos-Central Luzon Basin, Luzon Island, Philippines, Acta Palaeontologica Polonica 67 (4), pp. 917-947 : 932

Archivesica ? sp. 2

Fig. 14 .

Material.— Four specimens from block I ( NRM Mo 192676– 192679). Upper Miocene of the “shale quarry” within the Northern Cement Corporation quarry in Pangasinan province, Luzon, Philippines .

Dimensions (in mm).—NRM Mo 192676: L = 51.8, H = 43.2, W = 23.0; NRM Mo 192677: L = 50.6, H = 41.0, W = 24.1; NRM Mo 192678: L = 38.2, H = 31.4, W = 13.7; NRM Mo 192679: L = 17.2, H = 12.3, W = 7.2.

Description.—Short, oval shell, umbones elevated, prosogyrate, positioned at anterior 27–31% of total shell length; anterior margin acutely rounded, posterior margin wide, broadly rounded. External surface with fine growth increments, internal surface with radial striation; no lunular incision; hinge plate narrow, RV with three thick, short cardinal teeth: cardinal 1 displaced anteriorly, 3a just anterior to beak, pointing anteriorly, 3b just posterior to beak, pointing posteriorly; no subumbonal pit.

Remarks.—These specimens show an unusual combination of shell characters. The overall shape (short, oval, little inflation) resembles that of species of Wareniconcha or Calyptogena (see Krylova and Sahling 2006; Cosel and Olu 2009). But the hinge with its strong, thick, radiating teeth is very similar to those of Archivesica nankaiensis (Okutani, Kojima, and Ashi, 1996) , A. soyoae ( Okutani, 1957) , A. solidissima ( Okutani, Hashimoto, and Fujikura, 1992a) and A. okutanii ( Kojima and Ohta, 1997) , all of which, however, are much more elongated and inflated ( Okutani 1957; Okutani et al. 1992a; Kojima and Ohta 1997; Okutani et al. 1997; Sasaki et al. 2005). Furthermore, species of Archivesica possess a subumbonal pit, lacking in the present specimens. Therefore, we only hesitantly assign this species to Archivesica .

Figures

Fig. 14. The vesicomyid bivalve Archivesica? sp. 2 from Upper Miocene seep deposits of the Amlang Formation in Pangasinan province, Luzon, Philippines. A. NRM Mo 192676, large articulated specimen, view on LV showing interior posterior ridge (A1), dorsal view showing moderate inflation and lunule (A2). B. NRM Mo 192678, articulated specimen,view on LV showing general outline. C. NRM Mo 192677, isolated RV, view on hinge.