Microvoluta corona, Simone & Cunha, 2012

Simone, Luiz Ricardo L. & Cunha, Carlo M., 2012, Taxonomic study on the molluscs collected in Marion-Dufresne expedition (MD 55) to SE Brazil: Xenophoridae, Cypraeoidea, mitriforms and Terebridae (Caenogastropoda), Zoosystema 34 (4), pp. 745-781 : 768-770

Microvoluta corona n. sp.

( Fig. 7 E-G)

TYPE MATERIAL. — Holotype: Brazil, Espírito Santo, off Itaúnas, continental slope of Abrolhos , 19°01’S, 37°47’W, 1500-1575 m depth, MNHN 25243 ( Fig. 7 E-G) ( MD55 , stn DC79 , Bouchet, Leal & Métivier coll., 28.V.1987).

TYPE LOCALITY. — Brazil, Espírito Santo, off Itaúnas, continental slope of Abrolhos, 19°01’S, 37°47’W, 1500- 1575 m depth ( MD 55, stn DC 79).

DISTRIBUTION. — Known only from type locality.

ETYMOLOGY. — The specific epithet is derived from the Latin word “corona”, meaning crown, an allusion to the subsutural ornamentation of the shell.

DIAGNOSIS. — Shell up to 5.5 mm, elliptical (width c. 2 times length). Sculpture mainly axial, subsutural, uniform nodes, located on shoulder. Protoconch blunt, mammillary, with one whorl. Aperture wide, c. ½ shell length.

DESCRIPTION

Shell: size 5.5 mm, outline elliptical; width c. 54% of length. Colour pure white ( Fig. 7E, F ); surface smooth, glossy. Protoconch blunt, mammillate, comprising c. 6% of shell length and c. 20% of shell width; about two rounded, smooth, glossy whorls; suture unclear ( Fig.7E, F ); transition with teleoconch indistinct. Spire c. 44% of shell length; spire angle c. 55°. Teleoconch up to four whorls; each whorl strongly shouldered; area between shoulder and upper suture horizontal, comprising c. ¼ of whorl length; remaining area weakly concave, with almost straight and vertical profile.Sculpture uniform, large nodes on shoulder, producing weak axial threads, below nodes, gradually disappearing before inferior suture; c. 10 in penultimate whorl; interspaces of axial threads roundly concave, as wide as threads. Ventral region of body-whorl with anterior ⅔ smooth. Aperture elliptic, oblique c. 30° in relation to shell longitudinal axis; comprising c. 53% of shell length and c. 40% of shell width. Outer lip simple, rounded, thick; with small upper notch corresponding to shoulder ( Fig. 7E, G ). Inner lip weakly concave, callus inconspicuous; four oblique folds uniformly distributed and similar-sized in middle and inferior thirds, comprising c. 80% of inner lip area; upper folds more horizontal, becoming oblique towards canal ( Fig. 7G ). Canal wide and short; almost as wide as aperture width. No umbilicus.

MEASUREMENTS (in mm). — Holotype: 5.5 × 3.0.

HABITAT. — Sandy bottoms, 1500-1575 m depth.

REMARKS

Microvoluta corona n. sp. is somewhat similar to M. blakeana (Dall, 1889) from the Gulf of Mexico (146-1170 m depth), differing in having strong subsutural nodes, taller spire and wider aperture. Differs from M. intermedia Dall, 1890 , from the Caribbean, in being shorter, fewer whorls, by subsutural nodes proportionally larger and fewer, lacking subsutural spiral thread. Microvoluta corona n. sp. still differs from Peculator verconis Iredale, 1924 by its subsutural nodes, and by whorls forming shoulder.

The generic attribution is not absolutely secure, because only the type species of Microvoluta , M. australis Angas, 1877 , lacks subsutural nodes ( Pechar et al. 1980). However, most of the species attributed to this genus have subsutural nodes ( Bouchet & Kantor 2003). Microvoluta corona n. sp. has some similarities with above mentioned species, allowing the generic attribution, rather than other volutomitrid and even marginellid genera, such as protoconch mammillate of two whorls, and inner lip smooth inside.

DISCUSSION ON MITRIFORMS

The mitriform gastropods are not the most diverse group amongst the MD55 collected samples, and each species is represented by few and sometimes incomplete specimens.This is indicative that possibly they can be transported from shallower levels. The single exception is Nodicostellaria crassa , which was collected abundantly and alive. This species appears to be the dominant mitriform species in continental slope along the entire southeastern Brazilian coast, and one of the main gastropod predators.

As the above descriptions and taxonomic discussions demonstrate, the closest relatives to most species occur in northern Atlantic, mainly in Caribbean Sea. Despite the similarities, most species demonstrate to be different, which can indicate a relationship, but under different conditions in the western Atlantic deep-water environment, possibly because of the influence of large rivers like the Amazon River, oceanic currents, or some other environmental factor of isolation.

Superfamily CONOIDEA Fleming, 1822

Family MITROMORPHIDAE Casey, 1904

Figures

FIG. 7. — Costellariid and volutomitrid: A, Austromitra decresca n. sp., holotype MNHN 25239, apertural view (L 5.6 mm); B, same, dorsal view; C, same, detail of inner lip, apertural-slightly right view; D, paratype MZSP 102687, apertural view (L 5.8 mm); E, Microvoluta corona n. sp., holotype, MNHN 25243, apertural view (L 5.5 mm); F, same, dorsal view; G, same, details of aperture, apertural-slightly right view.