Thalassonerita hagai, 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 : 937

Thalassonerita hagai sp. nov.

Fig. 19 .

Zoobank LCID: urn:lsid:zoobank.org:act:5A82FE2C-D3D5-41FD-B011-9AD5924DE4B9

Etymology: For Takuma Haga (Tsukuba, Japan), who collected the specimens.

Type material: Holotype: NIGSPAL-032, specimen with some shell, aperture obscured by rock matrix. Paratypes: NRM Mo 192657, 192658, partially preserved specimens 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.— Type material only.

Dimensions (in mm).—NIGSPAL-032: W = 25.0, H = 17.3.

Diagnosis.—Shell large for genus, two whorls, sculpture of 13 widely spaced axial ribs on last whorl.

Description.—Large neritiform shell, up to 25.0 mm wide, at least two whorls, spire apparently flat; sculpture of 13 oblique axial ribs, interspaces between ribs 2–3 times the width of ribs, both ribs and interspaces covered by fine axial lirae.

Remarks.—The specimens have a thin outer layer that appears to differ in mineralogy from the remaining shell material, and such a layer has not been observed in other gastropods from the Northern Cement Corporation quarry. It is here interpreted as the calcitic outer layer typical of neritimorph gastropods. This is the first fossil record of Thalassonerita from the central Indo-West Pacific and with a width of 25.0 mm it is by far the largest Thalassonerita reported to date. Both the middle Eocene Thalassonerita eocenica Squires and Goedert, 1996 , from the Humptulips Formation in western Washington state, USA ( Squires and Goedert 1996; Hybertsen and Kiel 2018), and the type species Thalassonerita megastoma Moroni, 1966 , from the Upper Miocene of Italy, also reported from the Miocene of Barbados, reach only 10.0 mm in width ( Moroni 1966; Gill et al. 2005). An early Oligocene neritid reported from seep deposits in Peru reaches 8.5 mm in width ( Kiel et al. 2020b), and the extant Thalassonerita naticoides ( Clarke, 1989) has a maximum width of 12.5 mm ( Clarke 1989). Furthermore, all above mentioned species have less distinctive axial ornament than Thalassonerita hagai ; the extant T. naticoides is nearly smooth. An Early Cretaceous neritid reported from a seep deposit on the Crimean Peninsula reaches just over 20.0 mm in width, but is nearly smooth and might not have any direct phylogenetic relationships to Thalassonerita ( Kiel and Peckmann 2008) .

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

Figures

Fig.19. The phenacolepadid gastropod Thalassonerita hagai sp. nov., from Upper Miocene seep deposits of the Amlang Formation in Pangasinan province, Luzon, Philippines. NIGSPAL-032, holotype, in abapertural view (A1) and apical view (A2).