Acteocina decorata (Pilsbry, 1904)

Description

A small species of Acteocinidae, about 6.8 mm long and 3.9 mm in diameter. The shell is straightly cylindrical with a white body colour covered by a pale yellow cuticle, the cuticle being closely decorated with red-brown spiral lines. The sculpture is reduced to slight growth-lines, with no incised spiral lines on the shell itself. The spire is short, with about 3½ postnuclear whorls separated by a deeply channelled suture that descends only gently until the last whorl, where it descends more sharply. The aperture has the usual shape for the genus: the outer lip is moderately arched forward in the middle and retracted above, and deeply slit at the suture. The columella is callous, flattened, slightly concave, and bears a low fold above.

Distribution

Type locality: Hirado, in Hizen Province (present-day Hirado Island, Nagasaki Prefecture, western Japan). The original describer noted that no similar species had been reported from the northwest Pacific at the time. The types (ANSP No. 85,985) are based on No. 1,235 of Yoichiro Hirase's collection.

Etymology

The specific epithet decorata is Latin for "decorated" or "adorned", in reference to the red-brown spiral lines that ornament the shell's cuticle.

Remarks

The red-brown spiral pattern resides entirely in the outer cuticular layer, not in the shell wall itself. Specimens whose cuticle has been worn or lost no longer show this diagnostic colour pattern. Well-preserved shells are easily separated from other small acteocinids by the combination of a short spire and red-brown spiral lineolation.

---

References

• Tornatina decorata n. sp. (Pl. V, fig. 51), Pilsbry H.A. (1904). New Japanese marine Mollusca: Gastropoda. Proceedings of the Academy of Natural Sciences of Philadelphia, 56: 3-37, pls. I-VI.
• ツララガイ Acteocina (Tornatina) decorata (PILSBRY), 波部忠重. (1961). 続原色日本貝類図鑑. 保育社, 大阪. xii + 183 + 42 pp., 66 pls. [Habe T. (1961). Coloured illustrations of the shells of Japan (II). Hoikusha, Osaka.]
• ツララガイ Acteocina (Tornatina) decorata (Pilsbry, 1904), 奥谷喬司. (2000). 日本近海産貝類図鑑. 東海大学出版会.