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Collisella onychitis (Family Acmaeidae)

Banded Limpet

Distribution:

The Banded Limpet has a south-western Australian distribution pattern. It ranges from Ceduna, SA, to the Murchison River, central WA. (SA, WA)

Features:

The Banded Limpet's shell is oval, thick, and has a low peak. It is narrower at the rear of the shell. It grows to a length of 15-20mm and a width of 12-15mm. The shell is sculptured with about 20 radial ribs, either weak or strong, that grow closer to each other at the rear. The shell margin is thin and notched. The shell is often eroded, which obliterates the sculpture. It is a variable species in colour, shape, and sculpture.

The colour is white, cream or grey with brown radial rays. The spaces between the ribs are dark brown, often flecked with white. Inside the shell is white and porcellaneous in colour, with a light brown spatula and white muscle scar. Heavily eroded shells are very dark.

Ecology/Way of Life:

The Banded Limpet occurs at low tide levels and below, on rocks. It is common to abundant across its distribution range. The Banded Limpet is closely related to the Granulated Limpet and they have an almost identical radula pattern. However, both species can be distinguished on shell characters (Ponder & Creese, 1980, p.177-8).

Interaction with Humans/Threats:

The Banded Limpet appears to be common to abundant over its range, although its range is restricted to south-western Australia. It does not appear to be under threat from human interaction.

Other Comments:

Collisella onychitis, Menke, 1843. Also known as Notoacmea onychitis. Acmaea achates, Theile, 1930, is a synonym. Collisella comes from two Latin words, coll, meaning the neck, and sella or sedere, meaning to sit (like a saddle). Onychitis may come from the Greek word onychos, meaning a nail or claw. Onyx is an agate of different coloured bands of chalcedony. However, the word onychitis is used in medicine to describe the inflammation of the soft parts about the nail. So the species name may describe its banded pattern, or alternately, its nail-like appearance when weathered.

Further Reading:

Davey, K. (1998) A Photographic Guide to Seashore Life of Australia. p.83, New Holland Press, Sydney.

Wells, F.E. & Bryce, C.W. (1988). Seashells of Western Australia. p.38, Western Australian Museum.

Wilson, B.R. & Gillett, K. (1979). A Field Guide to Australian Shells: Prosobranch Gastropods. p.32, Reed.

Acknowledgments:

Text, map & photograph by Keith Davey.

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