Scaphander sibogae Schepman, 1913

Siegwald, Justine & Malaquias, Manuel António E., 2025, Bringing light into deep-sea biodiversity: a systematic revision and molecular phylogeny of the genus Scaphander Montfort, 1810 (Gastropoda: Cephalaspidea), with a focus on the Indo-Pacific, Zoological Journal of the Linnean Society 203, pp. 1-60 : 27-30

Scaphander sibogae Schepman, 1913

( Figs 10 , 16 , 17 ; Table 2)

Scaphander sibogae Schepman, 1913: 465 , pl. 31, fig. 10; Valdés 2008: 677 , figs 43, 44A, B, 45A–C.

Scaphander attenuatus — Valdés 2008: 677; Chaban et al. 2019a: 397.

Taxonomic history: Based on empty shells collected in Indonesia during the Siboga expedition , Schepman (1913) described the species S. attenuatus , S. sibogae , S. subglobosus , and a fourth species from a complete specimen, which he also named ‘ sibogae ’ but ascribed to the new genus Meloscaphander Schepman, 1913 as Meloscaphander sibogae Schepman, 1913 . Valdés (2008) considered S. attenuatus a synonym of S. sibogae because of similarities in their original descriptions and type material, but as discussed earlier (see S. cancellatus section) we provide evidence that S. attenuatus is, in fact, a synonym of S. cancellatus . Chaban et al. (2019a) suggested Meloscaphander to be a junior synonym of Scaphander , which was confirmed by Siegwald et al. (2022). This led Chaban et al. (2019a) to consider M. sibogae Schepman, 1913 a secondary homonym of S. sibogae Schepman, 1913 and to suggest the name S. attenuatus as the valid replacement name for S. sibogae Schepman, 1913 . However, in our opinion this was a misinterpretation of art. 23.3.5 of the Code ( ICZN 1999a,b), because the unavailable name would have been S. sibogae ( Schepman, 1913) , i.e. the name resulting from the synonymizing of Meloscaphander and Scaphander . Therefore, in accordance with ICZN (1999a: art. 23.3.5.) we consider the species name S. sibogae Schepman, 1913 available and the name S. sibogae ( Schepman, 1913) [= Meloscaphander sibogae Schepman, 1913 ], unavailable. Given that no synonym names are available for the homonym name S. sibogae ( Schepman, 1913) , we introduce the replacement name Scaphander tortuosus nom. nov. ( ICZN 1999a,b: arts 23.3.5. and 60.3.; see S. tortuosus nom. nov. section for further details).

Type material:Scaphander sibogae Schepman,1913 — Indonesia: Bali, Siboga expedition,station18, 7°25'12"S, 115°24'36"E, 1018m, 15 syntypes, ZMA.MOLL.138503 , H = 25 mm, images seen ( Fig.16A ) .

Other material examined: Indonesia: Tanimbar Islands, one spc., dissected, MNHN-IM-2019-7926, H = 30 mm; Sulawesi, Makassar Strait, one sh., MNHN-IM-2010-2080, H = 24 mm. Papua New Guinea: New Ireland, one spc., sequenced, MNHN-IM-2013-58331, H = 34 mm; east of Kotakot, one spc., dissected and sequenced MNHN-IM-2013-18549, H = 31 mm. Solomon Islands: northwest of Isabel Island, one spc., MNHN-IM-2019-7921, H = 27 mm; one spc., MNHN-IM-2019-11713, H = 21 mm; one spc., MNHN-IM-2019-11714, H = 25 mm; one spc., MNHN-IM-2019-11715, H = 19 mm; one spc., MNHN-IM-2019-11716, H = 24 mm; one spc., MNHN-IM-2019-11717,H = 23 mm;onespc.,MNHN-IM-2019-11718, H = 24.5 mm; one spc., sequenced, MNHN-IM-2013-52471, H = 25 mm; New Georgia, one spc., dissected and sequenced, MNHN-IM-2013-52477, H = 20 mm; one spc., sequenced, MNHN-IM-2019-7922, H = 17 mm. Vanuatu: Santo, Big Bay, one spc., sequenced, MNHN-IM-2019-7918, H = 34 mm; one spc., MNHN-IM-2019-11719, H = 32 mm.

Diagnosis: Shell rounded ovate, orange brown to dirty white. Spiral sculpture composed of darker brown ovoid punctations, often slightly interconnected. Apex rounded, with posterior edge of outer lip rising above it in a sharp wing. Rachidian teeth tetragonal. Prostate cylindrical, separated from penial chamber by thin prostatic duct. Thin penial papilla covered in soft warts and wrinkles.

Shell ( Fig. 16 ): Maximum H observed = 38 mm. Shell ovoid to rounded, only one whorl visible. Aperture wide, as long as shell, narrowing posteriorly. Apex rounded; spire concealed. Posterior edge of outer lip rising in a sharp wing protruding beyond apex. Parietal wall covered with thick, smooth white callus; thinner, white to semi-translucent in posterior half. Spiral sculpture composed of punctuated striations. Punctations ovoid, close together, often slightly interconnected. Thin, pale to warm orange brown periostracum, can be darker inside spiral punctation pits. Shell dirty white.

Radula ( Fig. 17A–C ): Radular formula 20 × 1.1.1 (H = 30 mm). Lateral teeth curved, with weak denticulation on inner edge. Rachidian teeth tetragonal, with developed upper cusps, slightly curved inwards.

Digestive tract ( Fig. 17D, E ): Salivary glands short to medium long; surface uneven. Paired gizzard plates sub-triangular, with rounded corners.

Male reproductive system ( Fig. 17F, G ): Penial chamber cylindrical, lined internally with longitudinal ridges between genital opening and prostatic duct. Eversible penial papilla located at prostatic duct entrance. Thin penial papilla with apical tip rounded, covered in soft warts and wrinkles. Penial chamber separated from prostate by thin prostatic duct, widening towards prostate. Prostate cylindrical, filled with spongy tissue, rounded at end.

Ecology: Found between 650 and 977 m depth. Feeds on foraminifera, tubicolous polychaetes, and smaller molluscs (gastropods, bivalves, and scaphopods) (present study).

Distribution ( Fig. 10 ): Western Pacific Ocean, from Indonesia ( Schepman 1913; present study), the Philippines ( Valdés 2008), Papua New Guinea, Solomon Islands, and Vanuatu (present study).

Remarks: The taxonomic history of Scaphander sibogae is complicated, owing to the fact that it was described by Schepman (1913) together with shells similar in both shape ( S. attenuatus and S. subglobosus ) and name ( M. sibogae , now S. tortuosus nom. nov.), which led to subsequent confusion (see S. cancellatus and S. tortuosus nom. nov. sections). The shell of S. sibogae is more ovoid, rather than sub-rectangular as in S. cancellatus , and can present dark brown punctations, whereas the punctations in S. cancellatus are of the same colour as the shell (see S. cancellatus section). The rachidian teeth in S. sibogae are more quadrate, with curved upper cusps, but in S. cancellatus these teeth are more elongated, H-shaped, with all cusps curved. Differences in the male reproductive system can also be found: S. sibogae has a simple cylindrical penial chamber and a muscular penial papilla, whereas S. cancellatus has a bulged penial chamber lined with soft warts around the prostatic duct, which is shorter in this species ( Figs 12F , 17F ).

The shell of S. sibogae is very similar to S. andamanicus . Their shells are similarly rounded, and the outer lip is raised in a wing-like structure above the apex, although the latter is sharper in S. sibogae , more rounded in S. andamanicus . However, owing to the lack of records for S. sibogae in the Andaman Sea or the Bay of Bengal, together with the scarceness of material for study and the absence of soft body parts for S. andamanicus to be compared molecularly and anatomically with S. sibogae , the species are both kept as valid for now. Nonetheless, further sampling in the Andaman Sea and Bay of Bengal might require this hypothesis to be revised.

Figures

Figure 10. Geographical distribution of Scaphander andamanicos, Scaphander cancellatos, Scaphander illecebrosos, and Scaphander sibogae. Geographical records are based on studied material and reliable literature records.

Figure 12. Anatomical details of Scaphander cancellatos. A, radula, Solomon Islands, west of Vella Lavella (MNHN-IM-2013-52474, H = 32 mm). B, rachidian teeth, Solomon Islands, east of San Cristobal (MNHN-IM-2009-6678, H = 18 mm). C, detail of lateral teeth, Indonesia, Tanimbar Islands (MNHN-IM-2019-7931, H = 28 mm). D, anterior part of digestive tract, Indonesia, Tanimbar Islands (MNHN-IM-2019-7925, H = 27 mm).E, gizzard plates (MNHN-IM-2019-7925, H = 27 mm). F, male reproductive system (MNHN-IM-2019-7925, H = 27 mm). G, lining of penial chamber, Japan, Tosa Bay (NSMT Mo-90588, H = 31 mm). Scale bars: A = 200 µm; B, C = 20 µm; D = 1 mm; E, F = 2 mm; G = 400 µm.

Figure 16. Shells and SEM image of the shell sculpture of Scaphander sibogae. A, Indonesia, Bali (syntype, ZMA.MOLL.138503, H = 25 mm; images taken by K.Hasegawa and courtesy of Naturalis Biodiversity Center). B, Indonesia, Sulawesi, Makassar Strait (MNHN-IM-2010-2080, H = 24 mm). C, Solomon Islands, northwest of Isabel (MNHN-IM-2013-52471, H = 25 mm). D, Vanuatu, Santo, Big Bay (MNHN-IM-2019-7918, H = 34 mm). E, Indonesia, Tanimbar Islands (MNHN-IM-2019-7926, H = 30 mm). F, Papua New Guinea, east of Kotakot (MNHN-IM-2013-18549, H = 31 mm). G, Indonesia, Sulawesi, Makassar Strait (MNHN-IM-2010-2080, H = 24 mm). H, Papua New Guinea, east of Kotakot (MNHN-IM-2013-18549, H = 31 mm). I, Solomon Islands, northwest of Isabel (MNHN-IM-2013-52471, H = 25 mm). J, Vanuatu, Santo, Big Bay (MNHN-IM-2019-11719, H = 32 mm). Scale bar: J = 200 µm.

Figure 17. Anatomical details of Scaphander sibogae. A, radula, Solomon Islands, New Georgia (MNHN-IM-2013-52477, H = 20 mm). B, rachidian teeth (MNHN-IM-2013-52477, H = 20 mm).C, detail of lateral teeth, Solomon Islands, northwest of Isabel (MNHN-IM-2013-52471, H = 25 mm). D, anterior part of digestive tract (MNHN-IM-2013-52477, H = 20 mm). E, gizzard plates, Papua New Guinea, east of Kotakot (MNHN-IM-2013-18549, H = 31 mm). F, male reproductive system (MNHN-IM-2013-52471, H = 25 mm).G, penial papilla (MNHN-IM-2013-18549, H = 31 mm). Scale bars: A, G = 200 µm; B = 20 µm; C = 10 µm; D, F = 1 mm; E = 2 mm.