Calliotropis arenosa
Creators: name: Helwerda, Renate Ariane
name: Wesselingh, Frank Pieter
name: Williams, Suzanne T.
Publisher: name: Zenodo
Year: 2014
Subjects: Biodiversity
Taxonomy
Animalia
Mollusca
Gastropoda
Calliotropidae
Calliotropis
Calliotropis arenosa

description: Calliotropis arenosa nov. spec.
(Figures 26–29)
Type material. holotype RGM 608.272. Paratype RGM 608.273 and RGM 608.275 (type locality); paratype RGM 608.274 (Anda 3).
Type locality. AndaDeVos, Bolinao province, Philippines, Santa Cruz Formation, Pliocene or Early Pleistocene.
Derivatio nominis. Named after the sediment covering adult shells.
Other material. Anda 2 (1); Anda 5 (1); Anda 6 (49); AndaDeVos (102); AndaClif3 (18).
Diagnosis. Shell conical, covered in sediment, H 3.4 mm, W 2.7 mm; P large, DN 0.19 mm); T sculpture of multiple axial ribs and two spiral ribs, with granules at intersections; suture canaliculate; aperture with three lamellae and a columellar denticle; umbilicus narrow.
Description. This species has a conical-shaped shell that is covered with a thin, even layer of fine sand from the early teleoconch onwards. This sand is most likely agglutinated by the live animal. The protoconch has a large, globose nucleus (DN 185–192 µm) and it is finely granular and consists of 1.0 whorls. The P/T boundary is marked by a thin varix. The teleoconch bears microscopic pustules. The first teleoconch whorl is sculpted with 15 axial ribs. Their interspaces are about three times as wide as their width. Sediment cover develops within the first 0.5 teleoconch whorl. Two spiral ribs appear on the second teleoconch whorl. The axial ribs develop granules at intersections with these spiral ribs. The whorl profile changes from round to angular as the spiral ribs become more pronounced. The area between the spiral ribs becomes slightly concave. The suture is canaliculate. The body whorl bears four additional spiral ribs. The area between the middle rib and basal rib is also slightly concave. The three basal ribs are slightly weaker than the three ribs on the preceding whorls. The base is slightly convex. The aperture is weakly nacreous and subcircular to subquadrate. The parietal margin is slightly convex and contains a thin callus and a weak knob on its upper part. The general shape of the outer lip is rounded, but the spiral ribs produce local angulations. The inner side of the outer lip contains two weak lamellae and a stronger basal lamella. The columellar lip is also rounded but the columella is nearly straight. A weak denticle is present at midpoint of columella in holotype, but absent in most other specimens. The umbilicus is narrow.
Differentiation. Calliotropis arenosa is most similar to the slightly taller C. acherontis Marshall, 1979 (Recent, southwest-Pacific), but the latter species does not agglutinate sand to the shell. Furthermore, the specimens figured by Marshall (1979) and Vilvens (2007) do not appear to have lamellae or a denticle in the aperture, while the larger specimens in the studied material, in which the aperture is not filled with sediment, always have lamellae and sometimes also have a denticle.
Remarks. The layer of sediment on the adults of this species is considered here as a characteristic of the species, because it is present in all adult material and its appearance, thickness and evenness is constant and similar in all adults. Furthermore, such a characteristic layer is not present in any other species of shells in the studied material. The origin of this layer of sediment remains speculative, but is perhaps facilitated by periostracal fluids, as it is in the Caenogastropod genus Scaliola Adams, 1860 (Healy & Wells 1998). One specimen in the studied material has grown wider whorls after a break in the shell, so injuries to snails of this species may sometimes alter shell development.
description: Published as part of Helwerda, Renate Ariane, Wesselingh, Frank Pieter & Williams, Suzanne T., 2014, On some Vetigastropoda (Mollusca, Gastropoda) from the Plio-Pleistocene of the Philippines with descriptions of three new species, pp. 101-135 in Zootaxa 3755 (2) on page 115, DOI: 10.11646/zootaxa.3755.2.1, http://zenodo.org/record/250959