Anctus prolatus, Simone, Luiz Ricardo L. & Casati, Rafael, 2013

Simone, Luiz Ricardo L. & Casati, Rafael, 2013, New land mollusk fauna from Serra da Capivara, Piauí, Brazil, with a new genus and five new species (Gastropoda: Orthalicoidea, Streptaxidae, Subulinidae), Zootaxa 3683 (2), pp. 145-158 : 151-153

Anctus prolatus new species

( Figs. 35–41 )

Types. Holotype MZSP 112450. Paratypes MZSP 111836, 3 shells (sta. P6), MZSP 112350, 1 young shell, 112362, 2 shells, 112372, 3 shells; all from type locality.

Type locality. BRAZIL. Piauí; Serra da Capivara ; Coronel José Dias municipality, close to Sítio do Mocó town, Cave Toca de Cima dos Pilão, 8°51’47.10”S 42°33’26.96”W (R. Casati col, 2012).

Diagnosis. Shell elongated, with width/length ratio of ~39%. Axial undulations relatively strong, almost forming sculpture. Peristome elongated, rectangular, lacking teeth. Umbilicus occluded by planar surface of inner lip.

Description. Shell of about 25 mm. Color cream, with sparse axial, pale brown bands. Periostracum not preserved. Outline bulimuloid; width ~39% of length. Protoconch of 2 whorls, opaque, conical, suture shallow; smooth, pigmented of dark brown ( Figs. 39–40 ); occupying ~3% of shell length and ~12% of shell width; border protoconch-teleoconch unclear, orthocline. Spire of ~7 flattened whorls, tall, being wider in last whorl ( Figs. 35, 40 ); angle ~40°; suture shallow, weakly marked. Sculpture uniform series of axial, narrow undulations, from suture to suture, ~ 40 in penultimate whorl; interspaces between undulations equivalent to their width. Peristome deflected outwards, expanding ~10% width of preceding whorl; aperture orthocline ( Figs. 36, 38, 41 ). Aperture narrow, rectangular, ~4 times longer than wide ( Figs. 35, 40, 41 ), occupying ~46% of shell length and ~35% of width; lacking teeth except for narrow thickness in inferior half of outer lip ( Figs. 40–41 ); outer lip mostly straight, with small rounded portions only in both ends; anterior region as narrow spatula; inner almost straight, weakly concave, superior third oblique and weakly convex, inferior 2/3 almost straight and narrow, as tube surrounding umbilicus. Callus thick, planar, simple ( Figs. 35, 38, 40 ). Umbilicus occluded by planar surface of inner lip, somewhat projected ventrally ( Figs. 35, 38, 41 ).

Measurements (in mm): Holotype ( Fig. 35–39 ): 25.2 by 10.1; paratype MZSP 111836: 20.1 by 9.3; MZSP 111836 ( Figs. 40–41 ): 24.1 by 10.8.

Distribution. Only known from type locality.

Habitat. Caatinga semi-dry environment; collected inside caves.

Material examined. Types. Non-type material from type locality MZSP: 112403, 10 shells, 112422, 1 shell, 112439, 1 shell.

Etymology. The specific epithet is derived from Latin prolatus , meaning extended, elongated, an allusion to the elongation of the shell of compared with other congener species.

Systematic remarks. The generic attribution to Anctus prolatus is based on the dark-brown protoconch, the axial sparse brown bands, the elliptical shape and the antero-posteriorly elongated peristome. The genus has only 3 species ( Breure, 1974; Simone, 2006). Anctus prolatus differs from A. angiostomus (Wagner, 1827) , from Bahia, in lacking a developed palatalis tooth in middle region of the outer lip, by the narrower umbilicus and by the slender outline (width/length ratio ~39%, against ~46% of A. angiostomus ). It differs from A. laminiferus (Ancey, 1888) , also from Bahia, in having a much narrower peristome, in having a wider umbilicus, and a narrower outline (width/ length ratio of A. laminiferus is ~47). It differs from A. surgillatus (Pfeiffer, 1857) , from Bolivia, in having more elongated aperture (46% of shell length, against ~37 of A. surgillatus ), and much narrower peristome (width/length ratio ~25% against 48% of A. surgillatus ). The elongation of the aperture of most Anctus species is for fixing and enchasing the shell to dry branches of plants ( Simone, 1998). This is a behavior that can be extrapolated to A. prolatus . Anctus prolatus , which expands the occurrence of the genus northwards in Brazilian territory, and is the first occurrence outside from Bahia state.

Figures

FIGURES 35 – 45. Type shells. Figs. 42 – 45, Anctus prolatus n. sp. holotype MZSP 112450 (L 25.2 mm); Fig. 35, frontal view; Fig. 36, same, right view; Fig. 37, same, dorsal view; Fig. 38, same, anterior view; Fig. 39, same, apical view; Fig. 40, paratype MZSP 111826 (L 24.1 mm), apertural view; Fig. 41, same, slightly left view; Figs. 42 – 45, Streptartemon molaris n. sp. shell of holotype MZSP 112451 (W 8.7 mm); Fig. 42, inferior view; Fig. 43, apical view; Fig. 44, apertural view; Fig. 45, same, detail of aperture.