Nerita squatina, DeVries, 2019

DeVries, Thomas J., 2019, Early Paleogene brackish-water molluscs from the Caballas Formation of the East Pisco Basin (Southern Peru), Journal of Natural History 53 (25), pp. 1533-1584 : 1552-1553

Nerita squatina sp. nov.

( Figure 4 (a – e))

Diagnosis

Spire flattened. Whorls with strong spiral cords. Columella with strong teeth, without papillae. Outer lip deeply fluted.

Description

(Based on fragments of multiple specimens): shell thick; length and width less than 20 mm. Spire flat to slightly sunken. Four whorls, angulate posteriorly and medially. Sculpture of about 15 steeply rounded primary spiral cords, subequal and evenly spaced anteriorly and posteriorly, alternatingly larger medially; rarely with secondary spiral cords. Interspaces flat. Axial sculpture absent except growth lines. Colour maculated black and cream. Apertural margin of columellar callus with strong anterior tooth, weaker medial tooth, and strong posterior bifid tooth; other teeth possibly present posteriorward. Abapertural portion of columellar callus with six well-spaced transversely elongate teeth, not aligned with apertural teeth; no papillae present. Outer lip with posterior inner edge bevelled and fluted; inflexions of bevel with small, spirally elongate spirally denticles along entire length. Base of columella separated from basal portion of bevelled outer lip by shallow sulcus.

Remarks

Nerita squatina does not resemble the smooth-shelled Nerita jayanca Olsson, 1944 from the upper Campanian Tortuga Formation in the Sechura Basin of northern Peru. Rather, the flattened shell form and arrangement of spiral cords of N. squatina resemble specimens of the late Eocene Nerita listrota Woodring, 1973 from Panama and the Paleocene to middle Eocene Nerita triangulata Gabb, 1869 from western North America, but some spiral cords on the latter two species are beaded and the columellar callus of those species is papillate ( Woodring 1973; Squires and Saul 2002).

The coarse adapertural and abapertural teeth on the columellar callus and the prominence of the spiral cords on N. squatina appear on modern species of the subgenera Nerita s. s., N. ( Ritena ) Gray, 1858, and N. ( Cymostyla ) Martens, 1887, closely related clades with a common ancestor inferred to have lived during the Oligocene or earlier ( Frey and Vermeij 2008; Frey 2010). Absent from the Caballas Formation species of Nerita , however, is the high spire characteristic of the Nerita s.s. - Ritena-Cymostyla clade ( Frey and Vermeij 2008).

Etymology

‘ Squatina ’, Latin noun meaning ‘ shark ’, referring to the row of adapertural teeth and row of parallel abapertural ridges on the columellar callus.

Material

All localities B8771 (type locality); all material fragmentary. UWBM 107577 , holotype, spire, W (5.7) ; UWBM 107646 , paratype, columellar callus teeth, W (6.2) ; UWBM 107647 , paratype, outer lip, W (7.8) ; UWBM 107648 , paratype, shoulder, W (8.5) ; UWBM 107649 , paratype, anterior of outer lip, W (10.1)

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Occurrence

Lower Paleogene, Cuenca Member, Caballas Formation, East Pisco Basin, southern Peru.

Figures

Figure 4. Gastropods from the Caballas Formation. (a–e) Nerita squatina sp. nov., B8771. (a) UWBM 107577, holotype, W 5.7 mm, spire. (b) UWBM 107648, paratype, W 8.5 mm, shoulder of last whorl. (c) UWBM 107649,paratype, W 10.1 mm, anterior of outer lip.(d) UWBM 107647,paratype,W 7.8 mm,inner surface of outer lip. (e) UWBM 107646, paratype, W 6.2 mm, columnar teeth. (f) Calyptraea cf. C. aperta Solander, 1766, UWBM 107578, B8772,W (diameter) 9.9 mm, external mould. (g) Ampullina ortoni Gabb, 1870, UWBM 107,627, B8772, L 36.8 mm, abapertural view, last whorl mostly missing; left margin annotated. (h–l) Melanella indicaformis sp. nov. (h) UWBM 107620, paratype, B8772, L 8.2 mm, apertural view. (i) UWBM 107619, paratype, B8769, L 9.4 mm, apertural/lateral view. (j) UWBM 107623, paratype, B8769,L 8.2 mm, apertural view. (k) UWBM 107618, paratype, B8772, L 10.6, abapertural view. (l) UWBM 107617, holotype, B8769, L 11.1 mm, abapertural view. (m–q) Potamides henryi sp. nov. (m) UWBM 107582, holotype, B8772, L 17.8 mm, lateral view. (n) UWBM 107582, W 6.9 mm, basal view. (o) UWBM 107586, paratype, B8771, L 11.2 mm, lateral view. (p) UWBM 107587, paratype, B8769, L 9.5 mm, abapertural view. (q) UWBM 107650, paratype, B8770, L 15.4 mm, lateral view, shell compressed. (r–t) Potamides janeae sp. nov., B8771.(r) UWBM 107579, holotype, L 9.0 mm, lateral view. (s) MUSM INV 249, L 8.8 mm, lateral and columellar view. (t) UWBM 107580, L 9.5 mm, layeral and columellar view. (u, v, x) Papposilenus utriculus gen.nov., sp. nov. (u) UWBM 107592,paratype, B8772, L 18.7 mm, oblique view of base. (v) UWBM 107589, holotype, B8772, L 25.5 mm, lateral view. (x) UWBM 107590, B8770, L 17.6 mm, lateral view.(w, y,z,jj) Rhinotamides everriculum sp.nov. (w) UWBM 107598,paratype, B8772,L 23.5 mm, abapertural view, juvenile. (y) UWBM 107593, holotype, B8769, L 21.1 mm, abapertural view. (z) UWBM 107594, paratype, B8772, L 19.4 mm, apertural view, posterior and anterior missing. (jj) UWBM 107593, apertural view.(aa,bb) Terebralia pauli gen. nov.sp.nov., UWBM 107599,holotype,B8771, L 9.2 mm.(aa) Abapertural view. (bb) Apertural view, outer lip missing. (cc) Terebralia marki gen. nov. sp. nov., UWBM 107600, holotype, B8771, L 9.8, lateral view. (dd–ii). Nodifaunus gainesi sp. nov. (dd) UWBM 107609, holotype, B8769, L 42.4 mm, apertural view. (ee) MUSM INV 264, paratype, B8772, L 31.0 mm, apertural view, anterior missing. (ff) UWBM 107609, abapertural view. (gg) UWBM 107612, paratype, B8770, L 14.2 mm, abapertural view, juvenile. (hh) UWBM 107612, apertural view. (ii) UWBM 107610, paratype, B8769, L 25.9 mm, apertural view, anterior missing.