Gastropteron sibogae Bergh, 1905

Valdés, Ángel, 2008, Deep-sea “ cephalaspidean ” heterobranchs (Gastropoda) from the tropical southwest Pacific, Mémoires du Muséum national d'Histoire naturelle 196, pp. 587-792 : 774-776

Gastropteron sibogae Bergh, 1905

Figs 95A, B, 96, 99

Gastropteron sibogae Bergh, 1905: 34-35 , pl. 9, figs 18-20.

TYPE MATERIAL. — Probably lost (not found at Zoologisk Museum, KØbenhavns Universitet, Copenhagen).

TYPE LOCALITY. — Paternoster Islands , Indonesia .

MATERIAL EXAMINED. — New Caledonia proper. BATHUS 1 : stn CP 661, 21°05’S, 165°50’E, 960-1100 m, 1 lv (Figs 95B, 96). Fiji. BORDAU 1 : stn CP 1490, 18°51’S, 178°32’W, 785-820 m, 1 lv (Fig. 95A) .

DISTRIBUTION. — Originally described from Paternoster Islands (= Kepulauan Tengah), Indonesia (Bergh 1905). Material herein collected in New Caledonia and Fiji (Fig. 99), in 820-960 m.

DESCRIPTION. — External morphology. Length 22 mm (largest specimen examined). Animal oval, with 2 large and thick ventro-lateral expansions (Figs 95A, 96A) that are probably used for swimming, as in other species of the genus.

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FIG. 95. External morphology and radular morphology of Gastropteron Kosse, 1813 . A, Gastropteron sibogae Bergh, 1905 , (22 mm), dorsal view, Fiji, BORDAU 1 stn CP 1490. B, Gastropteron sibogae Bergh, 1905 , specimen from New Caledonia, BATHUS 1 stn CP 661, scale bar = 300 Μm. C, Gastropteron bicornutum Baba & Tokioka, 1965 , specimen from Vanuatu, MUSORSTOM 8 stn CP 963, scale bar = 100 Μm.

FIG. 96. External morphology and anatomy of Gastropteron sibogae Bergh,1905 ,specimen from New Caledonia, BATHUS 1 stn CP 661. A, dorsal view of the preserved animal, scale bar = 3 mm. B, reproductive system,scale bar = 1 mm. Abbreviations: ag, albumen gland; am, ampulla; ap, anal papillae; bc, bursa

copulatrix; cs, cephalic shield; esg, external seminal groove; f, flagellum; gl, gill; mg, mucous gland; pa, parapodium; pn, penial sac; pr, prostate; sr, seminal receptacle; v, vagina.

The cephalic shield is oval with a small posterior protuberance. The dorsum is smooth. The viscera are visible through the tegument. On the posterior end of the body there is a single, conical process or flagellum. On the right side of the body there is a small, tripinnate gill, with 15 main pinnae. The gill is surrounded by the genital aperture anteriorly and the anal papillae posteriorly.

The colour of the living animal is unknown. Preserved specimens are uniformly orange to pale red with no traces of other pigments.

Anatomy. The radular formula is 18 x 5.0. 5 in a 22 mm long specimen (BATHUS 1 CP 661). The innermost lateral teeth are hamate, with a long, curved cusp, and smooth, with no denticles (Fig. 95B). The rest of the lateral teeth are also hamate and smooth, but considerably smaller in size.

The reproductive system is monaulic (Fig. 96B). The ampulla is very long and convoluted. It connects to the narrow, short post-ampullary duct. The post-ampullary duct continues distally to the common general atrium. Also entering the common atrium are the female glands and the bursa copulatrix. From the gonopore an open seminal groove runs anteriorly to the protrusible cephalic penis and the prostate. The prostate is very elongate and convoluted.

REMARKS. — The two specimens here examined match the characteristics of Gastropteron sibogae Bergh, 1905 , from Indonesia. The original description of G. sibogae (Bergh 1905) mentioned the presence of two large “foot wings” and a gill with 22 lamellae in a 50 mm long specimen. No drawings of the external morphology of the animal were included. The radular teeth of G. sibogae described by Bergh (1905) are hook-shaped and smooth, with no denticles, very similar to those of the specimens here examined. According to Gosliner (1989), the genus Gastropteron contains 11 valid species, all except G. sibogae having denticles on the radular teeth.

Gastropteron pacificum Bergh, 1894 is the only other deep-water species of the genus, found in the northeastern Pacific from the intertidal to about 500 m. Examination of specimens of G. pacificum (LACM 10343) revealed several differences between this species and G. sibogae , which include the absence of the posterior process and the presence of a much more complex gill with several branches in G. pacificum .