Sisonia frijellanae, Kiel & Fernando & Magtoto & Kase, 2022

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 : 934

Sisonia frijellanae sp. nov.

Fig. 17 .

Zoobank LCID: urn:lsid:zoobank.org:act:08086988-4440-4724-B293-0C12A48F2B82

Etymology: For Myra Vanessa A. Frijellana, Environmental Health and Safety Staff of the Northern Cement Corporation, who aided collecting at the quarry.

Type material: Holotype NIGSPAL-030, articulated specimen with exposed RV hinge . Paratypes: NRM Mo 192594–192596, 192598 (block B) , NRM Mo 192707 (block G), NRM Mo 192673, 192674 (block), articulated specimen with partially preserved shell, from the type locality and horizon.

Type locality: The “shale quarry” within the Northern Cement Corporation quarry in Pangasinan province, Luzon, Philippines .

Type horizon: Seep carbonate blocks enclosed in the Amlang Formation (Upper Miocene) .

Material.— 25 specimens from block B (NIGSPAL-031 [for a lot of 8 specimens]; NRM Mo 192594–192599, 192601– 192611) , 14 specimens from block G ( NRM Mo 192703– 192714) , 3 specimens from block I ( NRM Mo 192673– 192675) , one specimen from block J ( NRM Mo 192536). Upper Miocene of the “shale quarry” within the Northern Cement Corporation quarry in Pangasinan province, Luzon, Philippines .

Dimensions (in mm).—NIGSPAL-030: L = 39.6, H = 25.6, W = 20.7; NRM Mo 192595: L = 37.4, H = 24.7, W = 19.0; NRM Mo 192707: L = 32.4, H = 22.4, W = 13.5; NRM Mo 192674: L = 68.7, H = 40.0, W = 31.8; NRM Mo 192673: L = 48.5, H = 31.3, W (single) = 10.5.

Diagnosis.—Shell trapezoid to short modioliform in outline, strongly inflated, umbones in anterior third of shell, slightly elevated above hinge line, nearly orthogyrate; blunt ridges running from umbo to antero- and posterodorsal margins, area in between depressed; no lunule or escutcheon, ligament external; sculpture of fine growth increments only, internally with radiating striations; adductor muscle scars indistinct, pallial line entire, apparently no sinus; hinge with two strong, radiating cardinals in each valve.

Description.—Shell reaching 68.7 mm in length, strongly inflated, widest in posterior third of shell, outline short modioliform, dorsal and ventral margins subparallel, posterior margin truncate, anterior margin rounded to acutely rounded; ventral margin concave. Umbones broad, slightly elevated above hinge line, in anterior third of shell; ridge from umbo to posteroventral corner broad but distinct, ridge from umbo to anteroventral corner broad, indistinct; area between ridges deeply depressed, causing concavity of ventral margin; no sculpture except fine growth increments. Ligament short, resting on deeply incised nymphs; no lunule and escutcheon. Anterior adductor muscle scar indistinct, elongated pear-shaped, broadening ventrally, situated about midline of shell; pallial line starting just posterior of its ventral base; pallial line faintly impressed, moderately distant from shell margin, undulating, entire, apparently no sinus; anterior pedal retractor scar elongate, connected to adductor scar; posterior adductor muscle scar indistinct, shaped like an inverted comma, situated dorsally to groove running from umbo to posterior side of shell. Hinge plate narrow, subumbonal pit and two strong, short, radiating cardinals in each valve, RV with cardinal 1 and 3b, 3a apparently reduced, LV with cardinal 2a and 2b, cardinal 4 may be reduced.

Stratigraphic and geographic range. —Upper Miocene of Luzon, Philippines.

Class Gastropoda Cuvier, 1795

Unidentified limpet gastropod

Fig. 18A, B .

Material.— One poorly preserved specimen from block B ( NRM Mo 192585), 1 specimen from block F ( NRM Mo 192421), 1 specimen from block G ( NRM Mo 192715), 1 large specimen from block I ( NRM Mo 192656). Upper Miocene of the “shale quarry” within the Northern Cement Corporation quarry in Pangasinan province, Luzon, Philippines .

Dimensions (in mm).—NRM Mo 192421: L = 9.0, W = 7.5, H = 4.6; NRM Mo 192715: L = 6.2, W = 4.5, H = 2.5; NRM Mo 192656: L = 15.2, W = 11.8, H = 7.5.

Remarks.—Shape and the cancellate ornament of these specimens are very similar to species typically assigned to Bathyacmaea ( Okutani et al. 1992b; Jenkins et al. 2007a; Chen et al. 2019).

Figures

Fig. 17. The bivalve Sisonia frijellanae gen. et sp. nov. from Upper Miocene seep deposits of the Amlang Formation in Pangasinan province, Luzon, Philippines. A. NIGSPAL-030, holotype, articulated specimen with exposed RV hinge; view on exterior of RV (A1), close-up on hinge of RV (A2). B. NRM Mo 192594, hinge of isolated right valve. C. NRM Mo 192707, articulated specimen with ventral side missing, view on left valve (C1) and dorsal view showing inflation and short ligament (C2). D. NRM Mo 192595, paratype, articulated specimen, view on left valve (D1) and dorsal view (D2). E. NRM Mo 192596, paratype, close-up on anterior side of left valve of an articulated specimen, showing aams and aprs. F. NRM Mo 192598, paratype, hinge of isolated left valve. G. NRM Mo 192673, close-up on anterior side of isolated internal mold of left valve, showing aams and pallial line. H. NRM Mo 192596, paratype, close-up on anterior side of isolated internal mold of left valve, showing aams and internal, radial striation. I. NRM Mo 192674, paratype, very large specimen with mostly intact shell, views on right valve (I1), left valve (I2) and on dorsal side showing median sulcus and posterior ridge (I3). J. NRM Mo 192703, close-up on posterior side of RV showing pams and pallial line. K. NRM Mo 192704, close-up on posterior side of RV showing pams. Abbreviations: aams, anterior adductor muscle scar; aprs, anterior pedal retractor scar; pams, posterior adductor muscle scar; sub.pit, subumbonal pit; cardinal teeth numbers indicated in images A2, B and F.

Fig. 18. Limpets, neomphalids, and vetigastropods from Upper Miocene seep deposits of the Amlang Formation in Pangasinan province, Luzon, Philippines. A, B. Unidentified limpet gastropod. A. NRM Mo 192715, small specimen, mostly an internal mold. B. NRM Mo 192656, large specimen with sculpture. C. The neomphalin Retiskenea sp., NRM Mo 192540, apical view on specimen embedded in rock matrix. D, E. The seguenzoid Cataegis sp. D. NRM Mo 192666; note sculpture on D2. E. NRM Mo 192665, specimen showing the strong spiral ribs, in apical (E1) and abapertual (E2) views. F. The colloniid Homalopoma sp., NRM Mo 192583, views on entire shell (F1–F3) and close-up on spiral sculpture (F4).