Scaphander sibogae Schepman, 1913

Valdés, Ángel, 2008, Deep-sea “ cephalaspidean ” heterobranchs (Gastropoda) from the tropical southwest Pacific, Mémoires du Muséum national d'Histoire naturelle 196, pp. 587-792 : 677-678

Scaphander sibogae Schepman, 1913

Figs 43, 44A-B, 45A-C

Scaphander sibogae Schepman, 1913: 465 , pl. 31, fig. 10.

Synonym:

Scaphander attenuatus Schepman, 1913: 465-466 , pl. 31, fig. 11.

TYPE MATERIAL. — S. sibogae : 3 syntypes ZMA 3 . 13 112 . — S. attenuatus : 1 syntype ZMA 3.13 .115 .

TYPE LOCALITY. — S. sibogae : Indonesia, 07°28.2’S, 115°24.6’E, 1018 m [ Siboga : stn 018]. — S. attenuatus : Indonesia, 09°03.4’S, 119°56.7’E, 959 m [ Siboga : stn 052].

MATERIAL EXAMINED. — Philippines. MUSORSTOM 2: stn CP C); stn CH 281, 01°57’S, 119°00’E, 1120-1150 m, 1 dd — KAR- 55, 13°54’N, 119°58’E, 865 m, 1 dd. UBAR: stn CP 73, Tanimbar Islands , 08°29’S, 131°33’E, 855- Indonesia. The type material . — CORINDON: stn CH 280, 840 m, 1 dd (Fig. 45A); stn CP 87, 08°47’S, 130°49’E, 1017- Makassar , 01°59’S, 119°10’E, 715-800 m, 1 lv (Figs 44A, B, 45B, 1024 m, 1 dd.

DISTRIBUTION. — Originally described from Indonesia, in 959-1018 m. Material herein collected from Indonesia and the Philippines (Fig. 43), in 800-1120 m, live in 715-800 m.

DESCRIPTION. — Shell morphology. Length 30 mm, width 22 mm (largest specimen examined). Shell solid, oval to elongate, with convex sides (Fig. 44A). The widest region of the shell is near the middle area. Only 1 whorl visible, forming nearly the entire shell. Apex rounded, not umbilicate (Fig. 44B), with the aperture lip rising slightly from the left side, forming a short wing. Anterior end of the shell rounded. Aperture as long as the shell, wider anteriorly and narrowing abruptly at about 1/2-2/3 of the shell length. Columellar margin thickened, with no callus. Sculpture of a number of punctuated spiral grooves (Fig. 45A). The punctuations are small, oval, almost rectangular, and situated next to each other within each groove. The grooves are separated by gaps much wider than the grooves themselves, and occasionally narrower grooves are intercalated. Colour uniform brownish except for the shells that have lost the periostracum and are dirty white.

Anatomy. The digestive system contains 3 smooth gizzard plates, of which 2 are large and oval, whereas the third is elongate (Fig. 45C). The radular formula is 16 x 1.0. 1 in a specimen from Indonesia (CORINDON stn CH 280). The lateral teeth are elongate and hook-shaped, with a wide base bearing a blunt prolongation and a strong, long, curved cusp (Fig. 45B).

REMARKS. — Scaphander sibogae and Scaphander attenuatus were described based on empty shells collected in Indonesia. According to the original descriptions (Schepman 1913) these species have a similar sculpture but a different shell morphology. The shell of S. sibogae is comparatively shorter and wider and has a longer wing. However, examination of the type material revealed no consistent differences. The syntype of S. attenuatus is a better-preserved shell, with an intact periostracum, and the punctuations of the spiral grooves are larger and more clearly visible. On the other hand, the syntypes of S. sibogae are worn shells with smaller punctuations in the spiral grooves. Similar

differences have been observed in the material here examined, in which shells, or parts of shells, that are better preserved have larger punctuations. Differences in the general shape of the shell between S. sibogae and S. attenuatus probably represent intraspecific variation, and again similar variability has been observed in the newly collected material. It is clear that S. sibogae and S. attenuatus and the additional material here examined belong to this species. Following the Principle of the First Reviser (ICZN 1999: Article 24), the name S. sibogae is here selected as having precedence over S. attenuatus .

Scaphander sibogae differs from other Indo-Pacific species of the genus in shell morphology. The shell of S. sibogae is shorter, wider and more oval than that of S. japonicus . Also, the sculpture of S. sibogae is composed of spiral grooves with discrete punctuations, whereas in S. japonicus the punctuations are fused together within each groove. The radular teeth are similar to those of S. japonicus but their base is larger and bears a small prolongation absent in S. japonicus . Scaphander sibogae differs from S. mundus Watson, 1883 in having a more rounded shell and smaller punctuations. Anatomical differences include the much thinner and more elongate central gizzard plate in S. sibogae and the shape of the radular teeth, with a more elongate and curved cusp.