Magnella watsoni ( Dautzenberg, 1889 )

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

Magnella watsoni ( Dautzenberg, 1889)

( Figs. 22–23 )

Clathurella watsoni Dautzenberg, 1889: 29 , pl. 2, fig. 10.

Pleurotoma watsoni Dautzenberg, 1889 : Dautzenberg & Fischer (1896: 430); Dautzenberg & Fischer (1897b: 149); Dautzenberg (1927: 59).

Gymnobela watsoni Dautzenberg, 1889 : Bouchet & Warén (1980: 56, figs. 125, 245).

Type material: In Museé Océanographique de Monaco.

Type locality: Pico, Azores, Hirondelle (1887) sta. 112 (38°34’30”N, 30°26’30”W), 1287 m.

Material examined: 17183 [17] OP I # 44; 18480 [3] OP I # 45; 18481 [1] OP I # 50; 18482 [4] OP I # 50A; 14967 [2] OP I # 54; 18483 [4] OP I # 60; 18484 [7] OP I # 61; 18485 [1] OP I # 62; 18486 [1] OP I # 73; 15419 [1] OP I # 74; 18487 [3] OP I # 84; 18488 [2] OP II # 45; 18489 [4] OP II # 50A; 15578 [1] OP II # 54; 18490 [1] OP II # 60; 18491 [2] OP II # 61; 15548 [1] OP II # 69; 18492 [1] OP II # 73; 18493 [2] OP II # 75; 16794 [1] OP II # 79; 18494 [1] OP II # 80.

Description: Shell plump, biconical, white, up to 6.82 mm long. Protoconch with about 3.5 whorls. Protoconch 1 with spiral rows of tiny crosses. Protoconch 2 with diagonal cancellation on the lower 2/3 of the whorls and axial riblets crossed by very fine spiral threads on the upper third. Clear-cut proto-teleoconch boundary. Teleoconch with a nodulose subsutural spiral cord and a stronger one marking a slight shoulder on the upper half of the whorls. A slightly depressed area separates the subsutural spiral cord from the second one. Below the shoulder, about 20 weaker and flattened spiral cords cover the lower portion of the whorls and the base. As the ribs approach the fasciolar region they assume a more rounded conformation. Axial sculpture consists of 16–18 ribs (on the second whorl), forming small nodules where they cross the two stronger spiral cords. Secondary axial lines between the ribs, some also forming nodules where they cross the subsutural spiral cord. Suture well marked. Base short. Anal sinus not discernible. Inner lip reflected over parietal wall. Outer lip thick. Anterior siphonal canal slightly oblique, short and wide. Aperture elliptical.

Geographic distribution: Northeast Atlantic: Azores ( Dautzenberg, 1889; Dautzenberg & Fischer, 1896; Dautzenberg & Fischer, 1897b; Dautzenberg, 1927); Azores and France ( Bouchet & Warén, 1980). Southwest Atlantic: Campos Basin, Rio de Janeiro (this paper). Bathymetry: 698 m (this paper)– 2246 m ( Bouchet & Warén, 1980).

Discussion: Our specimens show a good fit to the type material ( Dautzenberg, 1889: pl.2, fig. 10). The only divergence observed would be the subsutural cord, which is stronger in our material. We have found some intraspecific variation on the axial sculpture in our material. In some specimens, the secondary axial lines were more pronounced giving the sculpture a more crowded appearance.

The closest species is M. malmii , from which it can be distinguished by a subsutural cord closer to the whorl shoulder and with fewer and more acute nodules. In addition, the spiral sculpture is fainter and the axial ribs are smooth, without nodules below the shoulder. In contrast, M. malmii has small nodules on the intersections of the spiral and axial sculpture, the subsutural cord has blunter and more numerous nodules and it is farther apart from the shoulder.

Magnella watsoni is reported for the first time in South Atlantic waters. It was previously known to occur only in Azores and France. Its bathymetric range is also increased. The shallowest depth previously reported was 1165 m ( Bouchet & Warén, 1980) and it has now been found at 698 m.

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.