Gymnobela blakeana Dall 1881

Gymnobela blakeana Dall, 1881

(Figs. 35–36)

Pleurotoma (Bela) blakeana Dall, 1881: 54.

Mangilia (Pleurotomella) {Gymnobela} blakeana Dall, 1881: Dall (1889: 126, pl. 10, fig. 1). Gymnobela aquilarum auct. non Watson, 1882: Bouchet & Warén (1980: 56, fig. 121).

Type material: Syntypes USNM 87427, MCZ 7151.

Type locality: Cape San Antonio, Cuba, 1170. Yucatan, Mexico. 1170 m.

Material examined: Type material and 16574 [1] OP II # 13-2; 16664 [1] OP II # 15; 16682 [1] OP II # 16-1.

Description: Shell plump, cream-colored, up to 10.02 mm long. Protoconch broken in our specimens, with only one whorl remaining, showing however diagonal cancellation on the lower portion of this whorl. Clear-cut proto-teleoconch boundary. Teleoconch whorls strongly angled on the upper third, forming a shoulder. Axial ribs more abundant on the first whorls, about 26–28 on the third whorl, and become less numerous as the shell grows, about 16–18 on the fifth whorl, forming blunt nodules where they cross the whorl shoulder. Axial ribs continue, reaching the aperture but weakening towards it. Numerous weak and somewhat flattened spiral cords sculpture the entire surface of the whorls evenly, including the base. Suture well marked. Base short. Anal sinus hardly discernible. Inner lip reflected over parietal wall. Outer lip thin. Anterior siphonal canal short, wide and slightly inflected. Aperture elliptical.

Geographic distribution: Northwest Atlantic: Cuba and Mexico (Dall, 1881; Dall, 1889); Saint Croix and Tortuga, Caribbean (Dall, 1889). Southwest Atlantic: Campos Basin, Rio de Janeiro (this paper). Bathymetry: 619 m (Dall, 1889)– 1170 m (Dall, 1881)

Discussion: This species is characterized by the short anterior siphonal canal, the plump profile and the strong shoulder on the teleoconch whorls. Our material matches well with the syntype of G. blakeana (fig. 36) and Dall’s original illustration (Dall, 1889, pl. X, fig. 1). The only discrepancies we observed are the presence of a very slight subsutural spiral cord and a sharper axial ornamentation on the syntype when compared to our individuals. We believe these differences to be intraspecific. The material illustrated by Bouchet & Warén (1980: 54, fig. 121) and identified as G. aquilarum (Watson, 1882) is very likely a young individual of this species. It appears to us that this was a misidentification, according to the type (fig. 37) and the original illustration of G. aquilarum (Watson, 1886, pl. XIII, fig. 4). Gymnobela aquilarum does not have a shoulder on the teleoconch whorls, and the axial sculpture is extremely faint, without forming the blunt nodules observed in G. blakeana.

Gymnobela blakeana is reported for the first time in South Atlantic waters (21–22ºS). It was previously known to occur in the Caribbean (17–21ºN). Its bathymetric range is also increased. The deepest depth previously reported was 1170 m (Dall, 1881) and it has now been found at 1664 m.