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Pisinna tumida (Tension-Woods, 1876)

Description: Shell small, solid, spire moderately rounded. Protoconch of 1½ - 2 whorls, sculptured with spiral rows of minute pits, with distinct junction with teleoconch. Teleoconch up to 4½ whorls, varying from weakly concave to weakly convex. Whorls sculptured with strong, oblique axial ribs, about 18 on last whorl, fading out on last ¼ of whorl, persisting onto base; spiral row of nodules below suture, sometimes with weak groove below. Aperture almost circular, outer lip with broad, low varix externally. Colour fawn or pink with three pale brown bands, one on nodules below suture, other 2 on base (barely visible in faded specimen figured here).

Size: Up to 3.0 mm in length.

Distribution: Endemic to Australia: Southern Queensland southwards and around southern Australia to south-western WA, including Tasmania.

Habitat: "Rarely found in the intertidal living on sublittoral algae, and dredged as dead shells on the continental shelf" (Ponder & Yoo, 1976). Generally uncommon, rare in NSW.

Comparison: This is similar to P. olivacea but has stronger axial ribs; there are three colour bands, not present on P. olivacea. It is subtidal and rare in NSW, while P. olivacea is intertidal and common. Also see Comparison of Pisinna species.

Synonymy: None.

Remarks: Ponder & Yoo (1976) have divided this species into three subspecies with isolated distributions. P. tumida tumida occurs from west of Wilsons Promontory to the eastern side of the Great Australian Bight, and Tasmania. P. tumida wilsoni (Ponder & Yoo, 1976) occurs in south-western WA. P. tumida simplicosta (Ponder & Yoo, 1976) occurs in southern Queensland and northern NSW, being known from only 3 lots.

Fig.1: 5007-1 Green Cape, Maria Island, Tasmania, 5.5 m (C.unreg)