Magnella extensa ( Dall, 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 : 15-16

Magnella extensa ( Dall, 1881)

( Figs. 24–26 )

Pleurotoma (Bela) blakeana extensa Dall, 1881: 55 : Dall (1889: 126, pl. 10, fig. 2); Pleurotomella extensa ( Dall, 1881) : Abbott (1974: 290, ind. 3452);

Gymnobela extensa ( Dall, 1881) : Absalão et al. (2005: 33, fig. 92); Rios (2009: 350, species 908); Pleurotoma (Defrancia) streptophora Watson, 1881: 464 .

Clathurella streptophora ( Watson, 1881) : Watson (1886: 356, pl. 19, fig. 8).

Type material: Syntypes MCZ 7146, MCZ 7147, MCZ 7148. Type locality: Cape San Antonio, Cuba, 755–1170 m; Yucatan, Mexico, Blake sta. 35 (23º 52’N, 88º 58’W), 1470 m.

Material examined: Type material and 18474 [1] OP II # 60; 18475 [1] OP II # 75; 18476 [2] OP II # 84; 18477 [1] OP II # 86; 18478 [1] OP I # 50A; 18479 [4] OP I # 75.

Description: Shell oblong-biconical, white, up to 5.08 mm long. Protoconch with about 3.5 whorls. Protoconch 1 with spiral rows of tiny crosses. Protoconch 2 with diagonal cancellation on the lower 3/4 of the whorls, and axial riblets crossed by very fine and faint spiral threads on the upper fourth. Clear-cut prototeleoconch boundary. Teleoconch with a strong subsutural spiral cord and another strong spiral cord on the upper half of the whorls. Axial sculpture consists of 14–16 axial ribs (on the fourth whorl), forming pointed nodules where they cross the spiral cords. Axial ribs extend over base. Shell surface with granules aligned spirally. Suture well marked. Base short, with nine weak spiral cordlets. Anal sinus not discernible. Outer lip relatively thick. Anterior siphonal canal oblique, very short and wide. Aperture elliptical.

Geographic distribution: Northwest Atlantic: Cuba ( Dall, 1881; Dall, 1889). Southwest Atlantic: Bahia, Espírito Santo and Rio de Janeiro ( Absalão et al., 2005); Campos Basin, Rio de Janeiro (this paper). Bathymetry: 450–2076 m ( Absalão et al., 2005).

Discussion: Our material matches well with the original illustration of the species ( Dall, 1889: pl. 10, fig. 2). When compared directly with the syntype (fig. 24), our specimens show a more prominent subsutural row of nodules and a stronger spiral ornamentation on the base. We believe these differences to represent intraspecific variation.

This species was originally described as a subspecies of M. blakeana . It can be distinguished from M. blakeana by its much thinner profile, glossy surface, less numerous spiral ornamentation and strong subsutural row of nodules.

Figures

FIGURES 20 – 26. 20, 21 — Magnella malmii (Dall, 1889), IBUFRJ 15980; 20 — 3,00 mm, whole shell; 21 — protoconch. Figures 22, 23 — Magnella watsoni (Dautzenberg, 1889), IBUFRJ 14967; 22 — 4.94 mm, whole shell; 23 — protoconch. Figures 24, 25, 26 — Magnella extensa (Dall, 1881); 24 — IBUFRJ 18474, 3.30 mm, whole shell; 25 — IBUFRJ 18474, protoconch; 26 — Syntype MCZ 7147. Scale bars: 20 and 24 = 500 μm; 21, 23 and 25 = 250 μm; 22 and 26 = 1 mm.