Piliscus commodus (Middendorff, 1851),
|Phylum:||Mollusca Linnaeus, 1758|
|Class:||Gastropoda Cuvier, 1795|
|Order:||Littorinimorpha Golikov & Starobogatov, 1975|
|Family:||Velutinidae Gray, 1840|
|Genus:||Piliscus Lovén, 1859|
|Synonyms:||Capulacmaea radiata (M. Sars, 1851)|
Description. Shell broad, irregularly cap-shaped, two whorled. Apex slightly shifted to right. Protoconch very small, white, one whorled, uncovered by peri- ostracum, hanging over upper third of back slope of shell. Last whorl covered by thin, light greyish-brown, membranaceous periostracum adherent to shell surface. Calcareous layer more developed than periostracum, bluish-grey; some specimens (especially from the southern part of geographic range) with violet bands of variable width radiating from apex. External coloration visible on inside of shell.
Aperture irregularly ovate, with periostracum projecting along the apertural margin. Axial sculpture consisting of elevated, irregular, distinct growth lines. Spiral sculpture lacking.
Measurements. A. T. Middendorff’s holotype: length 22 mm, width 19 mm, height 10 mm. Largest seen specimen: length 45 mm, width 35 mm, height 20 mm.
Remarks. Most investigators consider this species to be synonymous with Piliscus radiatus (M. Sars, 1851); however, the small protoconch in P. commodus, which forms a complete spire and is not adherent to the last whorl, and the geo¬graphic disjunction of their ranges are arguments for regarding them as separ¬ate species.
Distribution. From Peter the Great Bay and Hokkaido Island in the south and east to Point Barrow and the Pribilof Islands in the north and west. The spe¬cies occurs most abundantly in the Sea of Okhotsk.
Holotype No 1/11630 collected by A. T. Middendorff in 1844 in Tugursky Bay, the Sea of Okhotsk, is deposited with the gastropod collection at the Z. I.
Ecology. Intertidal zone to 500 m depth, usually 10-50 m; substrata varying from mud mixture and sand to rocks or more typically, stones.
- Gulbin V.V., Golikov A.N. A review of the prosobranch family Velutinidae in cold and temperate waters of the Northern Hemisphere. I. Capulacmaeinae