Gymnobela chyta ( Watson, 1881 )

Figueira, Raquel Medeiros Andrade & Absalão, Ricardo Silva, 2012, Deep-water Raphitomidae (Mollusca, Gastropoda, Conoidea) from the Campos Basin, southeast Brazil, Zootaxa 3527, pp. 1-27 : 18-19

Gymnobela chyta ( Watson, 1881)

( Figs. 31–32 )

Pleurotoma (Defrancia) chyta Watson, 1881: 466 .

Clathurella chyta ( Watson, 1881) : Watson (1886: 358, pl. 18, fig. 4); Gymnobela chyta ( Watson, 1881) : Bouchet & Warén (1980: 58, fig. 110); Pleurotoma (Defrancia) peripla Dall, 1881: 68 ; Dall (1889: 115, pl. 11, fig. 17).

Type material: Holotype BMNH 1887.2.9.1108

Type locality: West of Azores, sta. 73 (38º30’N, 31º14’W), 1829 m.

Material examined: 16469 [1] OP I # 13; 16421 [4] OP I # 15; 16440 [3] OP I # 16; 16594 [2] OP II # 13-2; 16617 [3] OP II # 15; 16541 [16] OP II # 16-1; 17205 [1] OP I # 44; 14961 [1] OP I # 54; 19178 [2] OP I # 61.

Description: Shell moderately plump, spire moderately high, yellowish, up to 44.48 mm long. Protoconch with about five whorls. Protoconch 1 with spiral rows of tiny crosses. Protoconch 2 with diagonal cancellation on the lower 2/3 of the whorls and arched axial riblets on the upper third. Clear-cut proto-teleoconch boundary. Teleoconch whorls with a strong shoulder at the upper part, forming a concave region between the suture and the whorl shoulder. Axial sculpture consists of many short prosocline axial riblets below the suture but not reaching the whorl shoulder, and 12–14 opisthocline axial folds (on the sixth whorl). Axial folds strongly angled on the whorl shoulder, extending to the base and becoming weaker toward the aperture. Numerous feeble spiral threads evenly sculpture the entire surface of the whorls below the shoulder, including the base. Concave region between the suture and the whorl shoulder crowded with minute granules. Suture moderately shallow. Base medium-sized. Anal sinus hardly discernible. Inner lip thin and reflected over parietal wall. Outer lip thin. Anterior siphonal canal short and wide. Aperture elliptical.

Geographic distribution: Northeast Atlantic: Azores ( Watson, 1886); Spain ( Bouchet & Warén, 1980). Northwest Atlantic: Mexico ( Dall, 1881; Dall, 1889). Southwest Atlantic: Campos Basin, Rio de Janeiro (this paper). Bathymetry: 750 m (this paper)– 2320 m ( Bouchet & Warén, 1980).

Discussion: Our material matches perfectly with the original illustration of the type of G. chyta ( Watson, 1886: pl. XVIII, fig. 4). Bouchet & Warén (1980: 51, fig. 110) also illustrated the same species, but showed it as slightly more slender.

Gymnobela chyta is reported for the first time in South Atlantic waters (21–22ºS). It was previously known to occur in Spain, Azores and Mexico (21ºN). Its bathymetric range is also increased. The shallowest depth previously reported was 1170 m ( Dall, 1881) and it has now been found at 750 m.

Figures

FIGURES 27 – 37. 27, 28 — Gymnobela atypha (Bush, 1893); 27 — IBUFRJ 16571, 20.42 mm, whole shell; 28 — IBUFRJ 18924, protoconch. Figures 29, 30 — Gymnobela bairdii (Verrill & Smith, 1884); 29 — IBUFRJ 16437, 22.48 mm, whole shell; 30 — IBUFRJ 18950, protoconch. Figures 31, 32 — Gymnobela chyta (Watson, 1881); 31 — IBUFRJ 16421, 31.54 mm, whole shell; 32 — IBUFRJ 19178, protoconch. Figures 33, 34 — Gymnobela xaioca n. sp.; 33 — Holotype MNRJ 30287, 20.94 mm, whole shell; 34 — Paratype IBUFRJ 16460, 14.34 mm, whole shell. Figures 35, 36 — Gymnobela blakeana Dall, 1881; 35 — IBUFRJ 16574, 10.02 mm, whole shell; 36 — Syntype USNM 87427. Figure 37 — Gymnobela aquilarum Watson, 1881, Holotype BMNH 1887.2. 9.724. Scale bars: 27 and 29 = 3 mm; 28, 30 and 32 = 300 μm; 31 and 33 = 4 mm; 34, 35, 36 and 37 = 2 mm.