Sabatia nivea (Watson, 1883)

Valdés, Ángel, 2008, Deep-sea “ cephalaspidean ” heterobranchs (Gastropoda) from the tropical southwest Pacific, Mémoires du Muséum national d'Histoire naturelle 196, pp. 587-792 : 682-685

Sabatia nivea (Watson, 1883)

Figs 46, 47, 49A, B

Scaphander niveus Watson, 1883: 343-345 .

TYPE MATERIAL. — Holotype BMNH 1887.2 .9.2182.

TYPE LOCALITY. — Southeast of the Philippines, 4°33’N, 127°6’E, 914 m [Challenger: stn 214] .

MATERIAL EXAMINED. — Philippines. The type material. Vanuatu. MUSORSTOM 8: stn DW 987 , 19°23’S, 169°35’E, Norfolk Ridge. BIOCAL: stn DW 70 , 23°25’S, 167°53’E, 965 m, 1040-1050 m, 5 dd (Fig. 46D); stn CP 1111 , 14°51’S, 167°14’E, 7 dd (Figs 46 C, E, F). 1210-1250 m, 3 dd, Figs 46 A, B ( LACM 153246 ) .

DISTRIBUTION. — Originally described from the Philippines, in 914 m (Watson 1883). New material herein collected in Vanuatu and New Caledonia (Fig. 47), in 914-1210 m.

DESCRIPTION. — Shell morphology. Length 29 mm, width 19 mm (largest specimen examined). Shell solid, oval to elongate, with convex sides (Figs 46A, D, E). Only 1 whorl visible in large and medium-sized shells (c. 10 mm or longer), forming the entire shell in adult shells (Fig. 46B). In smaller shells (less than 10 mm long) the protoconch

FIG. 46. Shell morphology of Sabatia nivea (Watson, 1883) . A, (29 mm), ventral view, Vanuatu, MUSORSTOM 8 stn CP 1111; B, same shell, posterior view; C, sculpture, New Caledonia, BIOCAL stn DW 70, scale bar = 100 Μm; D, (13 mm), ventral view, Vanuatu, MUSORSTOM 8 stn DW 987; E, juvenile shell, (5.5 mm), ventral view, New Caledonia, BIOCAL stn DW 70; F, protoconch, New Caledonia, BIOCAL stn DW 70, scale bar = 300 Μm.

is visible as well as up to 2 whorls of the spire (Fig. 46F). The protoconch is globose, about 0.6 whorl and 400 Μm in diameter. Apex rounded or slightly pointed, not umbilicate, with the aperture lip rising from the left side in larger specimens (10 mm or longer), forming a short wing (Figs 46A, D). In smaller specimens the outer lip ends at the same level (Figs 46E). Anterior end of the shell rounded. Aperture as long as the shell, wider anteriorly and narrower posteriorly. Columellar margin conspicuously thickened, with a large callus composed of numerous tubercles. The callus is only present on the anterior half of the aperture and is not present in small specimens (15 mm long or less), but some scattered tubercles may be present on the posterior half of the largest specimens. Sculpture of a number of spiral lines composed of overlapping punctuations (Fig. 46C). These lines are densely arranged and well marked near the apex, becoming more separate and undifferentiated towards the central part of the shell and disappearing from large areas of the anterior half. The lines reappear next to the posterior end where they are again well differentiated and densely arranged. Colour uniform dirty white.

Anatomy. The digestive system contains 3 smooth gizzard plates, 2 of which are large and oval, whereas the third is elongate (Fig. 49B). The radular formula is 14 x 1.0. 1 in a specimen from Vanuatu (MUSORSTOM 8 stn CP 1111). The lateral teeth are hook-shaped with a number of small denticles (Fig. 49A). They have a large base and a short and curved cusp.

REMARKS. — Watson (1883) described Scaphander niveus based on a single shell collected in the Philippines. The shell was described as oval with a wide aperture and sculpture of spiral grooves separated by large gaps. An examination of the holotype shows that the inner edge of the aperture has an eroded callus not illustrated in the figure published subsequently (Watson 1886: pl. 48, fig. 3). The holotype of S. niveus is very close to the material here examined from Vanuatu and New Caledonia and assigned to this species, the only difference being that the holotype is more eroded. This species is transferred to the genus Sabatia because of the presence of a callus on the internal edge of the aperture.

Sabatia nivea differs from Sabatia pustulosa Dall, 1895 (see below) in its shell morphology and anatomy. The shell of S. nivea has the callus on the anterior half of the aperture and it is absent in small specimens, whereas in S. pustulosa the callus is approximately in the middle region of the aperture and is visible in all specimens. Also, the shell of S. nivea is more elongate than that of S. pustulosa .