Atys semistriatus Pease, 1860

Atys semistriata Pease, 1860: 20 . Sowerby 1870: pl. 5, sp. 27. Smith 1872: 345. Pilsbry 1917: 217, fig. 5. Kay 1979: 426, figs 134A, B, 136A, 137A.

Atys (Alicula) semistriata — Pilsbry 1895: 267, pl. 28, fig. 30. Kobelt 1896: 20, pl. 6, fig. 11.

Atys semistriatus — Gosliner et al. 2008: 23.

Type locality. Hawaii .

Material examined. Hawaii, 1 shell examined, ZMB Moll 112.677 (paratype; see Fig. 12), H = 9.45 mm; Maui, Hawaii, live image taken, ZMBN 81656, H = 6 mm ; Tahiti, 1 shell examined, ZMBN 87082, H = 4.1 mm ; Tahiti, 1 spc. dissected, ZMBN 87082, H = 4.9 mm; the Philippines, 2 spcs dissected, MNHN, Paris (B31/ OT1042), H = 4.5 mm, 6.4 mm.

Animal (Fig. 1F): Body whitish-opaque, dark dots scattered over the body, abundant red blotches on the mantle; eyes visible.

Shell (Figs 2G, 11A): Maximum height 14 mm; whitish; thick, translucent, barrel-shape, oval, inflated, conspicuously wider at the centre, narrower posteriorly; anterior end protruded, posterior end truncated, apex perforate; spire sunken, umbilicated, aperture narrow posteriorly and broader anteriorly; spiral grooves at both ends only (anterior = 11–20, posterior = 11–16), which become closer towards the ends, spiral grooves deeper towards both ends forming step-like grooves, faint axial lines present.

Jaws: Present, crescent shape.

Radula (Figs 11B, C): Radular formula at mid-point 25–28 x 7–6.1.6–7; median tooth with broad base, triangular central cusp with membrane-like structure on both sides, shorter triangular lateral cusps present; outer lateral teeth hook-shaped, base with rectangular projection outwardly, grooves along both outer and inner margins, size decreases outwardly. There is no differentiation between inner and outer lateral teeth.

Gizzard plates (Figs 11D, E): Three gizzard plates; long and narrow; 21–31 ridges on each side of pseudorachis, V-shaped, ridges covered by single rows of tiny rods with pointed tips along top edge of ridge, both anterior and posterior sides of ridges smooth.

Male reproductive system (Fig. 11F): Total length 1.5 mm (H = 6.4 mm). Formed by three parts: prostate, seminal duct and penial region; prostate elongated-ovoid, bilobed, proximal lobe larger and opaque-yellowish, striations on proximal lobe sometimes present, distal lobe semi-translucent, creamy-white; prostate inserts laterally at the beginning of posterior part of seminal duct, seminal duct broad, anterior part semi-translucent, posterior part opaque-yellowish; penial region elongated, translucent, about same length as seminal duct, slightly narrower than seminal duct.

Ecology. Sandy bottom or on Halimeda beds between depth of 3–15 m (Gosliner et al. 2008; present study).

Geographical distribution. Madagascar, Indonesia, Malaysia, Japan, the Philippines, Papua New Guinea, New Caledonia, Guam, Tahiti, Hawaii (Kuroda & Habe 1952; Gosliner et al. 2008; present study).

Remarks. Shells of this species vary from thin and fragile (Pease 1860) to slightly thick but always semitranslucent. Pilsbry (1895) mentioned that Atys semistriatus is identical to Atys ehrenbergi Issel, 1869, which is a fossil found in the Red Sea. The con-specificity of these species remains to be confirmed. This species possesses an ovoid inflated shell, a feature shared with the type species Atys naucum, but its gizzard plates, radula and male reproductive system have different structure and arrangement (Bergh 1901; Lin 1997; Carlson & Hoff 1999).