Melanella indicaformis, 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 : 1555-1556

Melanella indicaformis sp. nov.

( Figure 4 (h – l))

Diagnosis

Shell small, elongate. Whorls smooth, flat-sided. Aperture oval, elongate, without anterior or posterior canals. Columella smooth, umbilicus absent.

Description

Shell length less than 15 mm, elongate, spire angle about 15°. Protoconch conical, about two smooth whorls. Teleoconch with about five whorls; whorls smooth, glossy, flat-sided to slightly convex, sometimes weakly turreted, thick; spire sometimes bent. Sutures adpressed; short crimped sutural collar sometimes overlaps preceding whorl. No spiral or axial sculpture. Base smooth, evenly rounded, set apart from rest of whorl by weak or moderately strong angulation. Aperture oval, twice as long as wide. Parietal callus strong; columellar callus thin; basal lip thickened, continuous with base of columella. Outer lip moderately thick, without teeth. Umbilicus absent.

Remarks

Species of Melanella have been reported from Paleocene rocks in New Zealand ( Finlay and Marwick 1937) and Antarctica ( Stillwell et al. 2004) and Eocene and Oligocene strata from North America ( MacNeil and Dockery 1984; Garvie 1996) and New Zealand ( Maxwell 1992).

A species similar to Melanella indicaformis was provisionally assigned to Pseudomelania by Olsson (1944): P. simplex Olsson, 1944 , found in upper Campanian beds of the Tortuga Formation in the Sechura Basin of northern Peru. The Tortuga Formation species is longer than the Caballas Formation species (length 18 mm vs 12 mm) and has nearly microscopic spiral threads, but the convexity of the spire, the glossy surface, and thickened inner lip are shared characters. A late Eocene species with a similar form, Bayania epelys Woodring, 1973 from the Canal Zone of Panama, differs from the Caballas Formation Melanella indicaformis by having faint spiral sculpture on the last whorl and a very shallow recurved siphonal notch. An early Oligocene species from the Talara Basin of northern Peru, Pachychilus canoaensis Olsson, 1931 , from the estuarine and freshwater Bravo Grits of the Mancora Formation, also resembles M. indicaformis and may be referable to Melanella .

Modern species of Eulimidae, including Melanella , are noted for their parasitism of echinoderms ( Warén 1983). Echinoderms are noted for their intolerance of brackish conditions, although some extant brackish-water echinoderms do exist ( Turner and Meyer 1980). No echinoderms have been encountered in beds of the Cuenca Member, despite an abundance of Melanella shells.

Etymology

‘ Indica ’, referencing the long-grained variety of rice that this species resembles.

Material

UWBM 107617 , holotype, B8769 (type locality), L 11.1, W 4.1 ; remainder are paratypes: UWBM 107618 , B8772, L 10.6, W 4.1 ; UWBM 107619 , B8769, L 9.4, W 3.6 ; UWBM 107620 , B8772, L 8.2, W 3.1 ; UWBM 107621 , B8772, L 8.7, W 3.2 ; UWBM 107622 , B8769, L (8.4), W (4.7) ; UWBM 107623 , B8769, L 8.2, W 3.3 ; UWBM 107624 , B8772, L 6.0, W 2.8 ; UWBM 107625 , B8772, L 5.0, W 2.6 ; UWBM 107626 , B8770, L 4.5, W 2.4 ; MUSM INV 266 , B8772, L 8.4, W 3.3 ; MUSM INV 267 , B8769, L (9.0), W 3.4 ; MUSM INV 268 , B8772, L 6.1, W 2.6

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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.