Mohicanus, Simone, Luiz Ricardo L., 2012

Simone, Luiz Ricardo L., 2012, Two new species of Tornidae (Caenogastropoda, Rissooidea) from Espirito Santo, Brazil, ZooKeys 238, pp. 77-85 : 78-80

Cyclostremiscus mohicanus sp. n. Figs 1-15

Types.

Holotype MZSP 106551 (Figs 1-5). Paratypes: 106552, 16 shells from type locality.

Type locality.

BRAZIL. Espírito Santo; São Mateus, Guriri, 18°47'S, 32°39'W, 3 m depth.

Diagnosis.

Shell of about 2.5 mm; almost planispiral. Three carina-like spiral threads somewhat equidistant; superior surface smooth or with scanty spiral cords. Periphery smooth except threads. Peri-umbilical area with string spiral cords. Periostracum with aligned series of tall rods on spiral threads.

Description.

Shell. Up to ~2.5 mm, discoid; height ~52% of maximum width (Figs 3, 10, 12). Color pure white, weakly translucent (Figs 1, 2, 5, 6). Protoconch of 2 whorls, weakly-turbiform (Figs 4, 10, 11, 15); whorls of rounded profile, suture shallow; surface glossy, smooth; occupying ~10% of shell size; located almost central, weakly dislocated towards right. Transition protoconch-teleoconch unclear (Fig. 15). Spire weakly elevated, with ~45% of shell width; ~15% of shell height. Teleoconch up to 2.5 whorls, uniformly growing weakly planispiral, bearing three somewhat equidistant carinas (Figs 9, 10, 11, 12); peripheral carina as tallest, profile blunt, ~100°, located in middle level of last whorl, inflating ~15% shell width; inferior carina similar to peripheral carina, located midway between this and peri-umbilical slope (Figs 10, 12, 13); superior carina with ~half size as peripheral carina, located midway between this and adjacent suture (Figs 6, 8, 9, 11); between carinas somewhat planar surface, being weakly elevated in carina’s base. Sculpture superior to peripheral carina absent (Figs 11, 14) to series of narrow, low, obsolete spiral cords (Figs 6, 8), varying from zero (surface smooth, Fig. 14) to ~10 (Fig. 8); interspaces between spiral cords ~1/4 their width; sculpture inferior to peripheral carina absent (smooth). Umbilicum widely opened; maximum diameter ~30% shell width; flanking by strong, somewhat planar slope; sculptured from 1 to 5 spiral cords, with interspaces ~3 times their width (Figs 5, 7, 12, 13). Aperture weakly prosocline (Figs 4, 9, 11, 13); rounded, weakly pentangular, i.e., bearing somewhat equidistant blunt angles produced by three carinas and umbilical slope (Figs 10, 12); with ~35% shell width, ~70% of shell height. Callus practically absent, weakly covering adjacent whorl in apertural implantation.

Periostracum (Figs 1-5). Opaque, transparent, color pale beige. Series of tall rods aligned on three carinas; rods of peripheral carina augmenting ~10% shell width (Figs 1, 2), about twice taller than wide, tip rounded, slightly broader than base; rods of superior carina similar to those of peripheral carina, with ~80% of their size (Figs 3, 4); rods of inferior carina also similar to those of peripheral carina, with ~30% their height and ~60% their width (Figs 3, 5). Each rod blade-like, flexible, located close to each other from same carina, forming tall flexible ridge on each carina. Periostracum ridge on three carinas suddenly finishing at apertural level. On aperture, region between ridge of superior carina and insertion of outer lip in adjacent preceding whorl a small region with ridge of peripheral ridge reabsorbed, forming anal notch with ~1/5 of aperture size (Figs 1, 2, 5).

Measurements (in mm). Holotype: 2.8 by 0.9; paratype 106552 (Fig. 10): 1.7 by 0.8.

Distribution.

Only known from type locality.

Habitat

. Sandy bottoms, 3 m depth (no living specimens).

Material examined.

Types.

Discussion.

Cyclostremiscus mohicanus is similar to Cyclostremiscus beauii (Fischer, 1857) ( Rosenberg et al. 2009; Rubio et al. 2011) from Florida and Caribbean. It differs by the smoother superior surface, lacking so developed spiral cords, the contrary happens in the umbilicum, in such that of Cyclostremiscus mohicanus has a series of spiral cords, while Cyclostremiscus beauii has only growth lines; the size is also different, as Cyclostremiscus mohicanus has about 3 mm, while Cyclostremiscus beauii reaches 9-10 mm. Cyclostremiscus mohicanus also resembles Cyclostremiscus pentagonus (Gabb, 1873), also from Caribbean, it differs by the more developed spiral sculpture in the superior shell surface, by the peri-umbilical spiral sculpture, in being slightly taller (height/width tax= ~52% against ~48% of Cyclostremiscus pentagonus ), and in having the peripheral carina slightly more elevated. Cyclostremiscus pentagonus has been referred as occurring in south Brazil ( Rios 2009: 59, in Porto Belo, Santa Catarina; Rubio et al. 2011: 91); as that material was not found, this record is here considered doubtful, but possibly they are of Cyclostremiscus mohicanus . Another important difference between Cyclostremiscus mohicanus and Cyclostremiscus pentagonus is the protoconch, it has ~2 whorls (Fig. 15), while that of Cyclostremiscus pentagonus is ~0.5 whorl longer ( Rubio et al. 2011, fig. 46F). Cyclostremiscus mohicanus is also somewhat similar to Cyclostremiscus trilix (Bursh, 1885), sharing the size and the carinas shape; however, it differs from that species in lacking the microtubercles on the protoconch, in having spiral sculpture in surface between suture and superior carina, and in being taller (height/width tax= ~52% against ~42% of Cyclostremiscus trilix ).

The periostracum bearing expansions are relatively common in living and fresh-died specimens of tornids. However, a periostracum with the Cyclostremiscus mohicanus arrangement appears to be novelty. Nothing like that has been found in other congeneric species. Cyclostremiscus mohicanus clearly belongs to the "group 1" as defined by Rubio et al. (2011: 84), which encompasses carinate species of the genus, with 2 or 3 peripheral carinas. Possibly all carinas of those species are base of periostracal expansions like those of Cyclostremiscus mohicanus .