Gymnobela atypha ( Bush, 1893 )

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 : 16-17

Gymnobela atypha ( Bush, 1893)

( Figs. 27–28 )

Pleurotomella atypha Bush, 1893: 205 , pl. 1, fig. 3.

Type material: Syntypes MCZ 6892, MCZ 187276

Type locality: Off Cape Fear, North Carolina, USA. Sta. 325 (33º35’20”N, 76º00’W, 1183 m); Sta. 326 (33º42’15”N, 76º00’50”W, 848 m).

Material examined: 18923 [3] OP II # 75; 18924 [2] OP I # 60; 18925 [4] OP II # 45; 18926 [3] OP II # 45; 18928 [1] OP II # 52; 18929 [3] OP I # 62; 18930 [2] OP I # 45; 18931 [2] OP II # 61; 18932 [2] OP I # 61; 18933 [2] OP I # 50; 18934 [3] OP I # 75; 16386 [6] OP II # 13-1; 16571 [3] OP II # 13-2; 16711 [1] OP II # 3-1; 16394 [2] OP I # 13.

Description: Shell slender, spire tall, white, up to 20.42 mm long. Protoconch with about four whorls. Protoconch 1 with spiral rows of tiny crosses. Protoconch 2 with diagonal cancellation on the lower 3/4 of the whorls and arched axial riblets. Clear-cut proto-teleoconch boundary. Teleoconch whorl middle angled. Region below the suture with a slight collar bulge showing several short arched axial riblets. Below the shoulder, about 12–14 strong widely spaced axial folds (on the seventh whorl) that enter a bit onto the base. Numerous low spiral cordlets cover the entire surface of the whorls below the shoulder, including the base. Shell surface with spiral rows of minute granules. Suture shallow. Base medium-sized. Anal sinus indiscernible. Inner lip thin, reflected over parietal wall. Outer lip thin. Anterior siphonal canal medium-sized and wide. Aperture elliptical.

Geographic distribution: Northwest Atlantic: North Carolina, USA ( Bush, 1893). Southwest Atlantic: Campos Basin, Rio de Janeiro (this paper). Bathymetry: 848 m ( Bush, 1893)– 1650 m (this paper).

Discussion: This species is characterized by a slender profile, weakly shouldered whorls, faint spiral sculpture and strong axial folds. Our material matches perfectly with the original illustration of the type of G. atypha ( Bush, 1893: pl II, fig. 3) and its description ( Bush, 1893: 205).

Gymnobela atypha is reported for the first time in South Atlantic waters (21–22ºS). It was previously known to occur only in the United States (33ºN). Its bathymetric range is also increased. The deepest depth previously reported was 1183 m ( Bush, 1893) and it has now been found at 1650 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.