Astyris atacamensis, Araya, Juan Francisco, Catalán, Ricardo & Aliaga, Juan Antonio, 2016

Araya, Juan Francisco, Catalán, Ricardo & Aliaga, Juan Antonio, 2016, A new deep-water Astyris species (Buccinoidea: Columbellidae) from the southeastern Pacific, Zootaxa 4139 (1) : -

Astyris atacamensis new species

Fig. 1

Type material. Holotype: SBNHM 460092 (H: 10.6, D: 6.7 and LW: 8.3 mm); paratypes: SBNHM 460093 (1 specimen), MPCCL 0 1062016 (4 specimens), MZUC 37641 (4 specimens), MNHNCL 202493 (7 specimens); all from the type locality.

Type locality. 20 km NW off Huasco (28°14'93'' S; 71°17'50'' W, 404–409 m), Región de Atacama, northern Chile. Leg. Ricardo Catalán, February 3, 2000.

Etymology. The specific name of Astyris atacamensis refers to presence of this species on the continental shelf of the Región de Atacama, northern Chile.

Diagnosis. Shell small (up to 11.1 mm long), thick, stout, with 4 to 5 rounded and slightly angulated whorls, often decollate; with sculpture of fine growth lines; spiral sculpture of very fine spiral grooves most noticeable on base of shell. Aperture wide, oval; outer lip sharp, in mature specimens with minute internal lirae; siphonal canal broad and straight.

Description. Shell small (H 5.8 to 11.1 mm), thick, stout, with 4 to 5 weakly convex whorls; outline conic; sutures impressed. Measurements from fifty randomly chosen specimens: H 5.8–8.3– 11.1 mm, D 3.5–5.3– 7.1 mm, and height of last whorl 4.5–6.5– 8.7 mm (minimum–average–maximum). Taking into account that most of the shells had the first whorls eroded, we could observe at most 5 whorls in the better preserved shells, with a bit over 4 whorls remaining in most specimens. Colour pale tan; earlier whorls slightly paler, showing indistinct spiral bands. Spire short, decollate, about two-fifths of total height; spire angle a bit less than 45°. Protoconch and early whorls eroded. Teleoconch smooth and slightly glossy, except for fine, irregular axial growth lines crossed by spiral sculpture of very fine, barely visible grooves; grooves cover almost entire exterior surface, coarsest and most noticeable on base. Last whorl large, about three-fourths of shell height, slightly convex, angulated near the base, concave below; maximum width at about one third from anterior end. Aperture prosocline, oval, slightly rectangular, posteriorly acuminate; aperture height slightly more than half of shell height. Parietal callus slightly thickened, concave. Outer lip sharp, simple, outline weakly convex, weakly concave over upper third, then swinging forwards weakly to suture; about 8 to 12 lirae inside outer lip; columella without denticles, callous. Siphonal canal short, very wide, anteriorly with rounded siphonal aperture.

Distribution and habitat. Shells of this species (no live specimens) were found in greenish mud, from soft bottoms off Puerto Flamenco (28°14'93'' S; 71°17'50'' W), Región de Atacama to off Tongoy (30°11'36''S; 71°33'25''W), Región de Coquimbo, Chile, from depths of 180 to 470 m. A single specimen, recently collected from sediments of the Bahía Inglesa Formation (Miocene to Pliocene) at Quebrada Blanca (27°03’55” S; 70°47’30” W), near Caldera, Chile may represent the oldest record for this species (Nielsen et al., unpublished).

Remarks. All of the specimens examined have the apex eroded to varying degrees, all of them lacking the protoconch and part of the earlier whorls. The definite generic assignment is thus still preliminary, but they agree partially with the description given by Garcia (2009) for Astyris . The distinctive broad shell shape, with a wide siphonal canal, is quite distinctive and different from all the other known columbellid species from the southeastern Pacific. Astyris atacamensis sp. n. is similar in shell characters only to Astyris permodesta ( Dall, 1890) , a species described from deep water in the northeastern Pacific ( Dall, 1890, Thorsson 2002). The new species differs from A. permodesta ( Fig. 2 ) in shell shape (slightly angulated versus convex whorls), with a last whorl slightly concave in A. atacamensis and compressed below in A. permodesta (producing a differentiated/protruding siphonal canal in this species); in the thickness of shell and lip (thin in A. permodesta and thick in A. atacamensis ; most visible at the upper end of outer lip), a slightly different aperture outline (product of the more convex last whorl in A. permodesta , slightly angulated in the new species), a thick columella (not callous in A. permodesta ), in the presence of lirae in the interior border of the outer lip in the new species (absent in A. permodesta ) and, particularly, in having a broader and less constricted siphonal canal, with a more pronounced columellar fold in the new species (absent in A. permodesta ). Furthermore, the habitat of the new species also seems to differ from that of Astyris permodesta , which is unusual in that it has been described from reducing environments, recorded along with species of large vesicomyid bivalves of the genus Calyptogena Dall, 1891 ( McLean, 1996) .

This new species thus represents the first record in Chile of the genus Astyris , previously unknown from the southeastern Pacific. Further sediment sampling in the area will probably reveal more molluscan species to be discovered and described, particularly micromollusks, as described by Araya & Geiger (2013).

Figures

FIGURE 1. Astyris atacamensis n. sp., off Huasco, Chile, 404 – 409 m depth. A – E. Holotype SBMNH 456358. F – I. Paratype SBMNH 452239.

FIGURE 2. Astyris permodesta (Dall, 1890). A – E. Holotype, USNM 96526, north of Santa Rosa Isl., Channel Islands, California, USA, 276 fms [504.7 m], mud. F – G. SBMNH 356555, Santa Monica Basin, off California.