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February 2021

Frilly Feet and Fragile.

I think this is a gastropod seen in the shallows at Raby Bay on an incoming tide. Its shell was around 4cm long. Can you tell me its name?

Answer

Rose Petal Bubble Snail, showing its frilly parapodia. Photo: Ursula Whyman.

An egg mass of a Rose Petal Bubble Snail, containing numerous eggs. Photo: Gary Cranitch.

This gorgeous gastropod, known scientifically as Hydratina physis, is a marine snail that goes by a few common names, including "Rose Petal Bubble Snail” and “Green-Lined Paper Bubble”. These namesrefer to the frilly folds on the foot and the thin, fragile, bulbous (bubble-like) shell.

Many species of marine gastropods have similar types of fleshy frills, called parapodia to aid movement. Although these ruffles give it a delicate appearance, this snail is carnivorous and preys on bristle worms and other sand dwelling marine invertebrates such as slugs.

These snails may be seen in large numbers during the summer to early autumn when they congregate in the sandy shallows to breed and lay their eggs. This is quite a sight as individuals lay a distinctive mass of white eggs that bunch together to form a pile. The snails will balance the egg mass on their frilly mantle before finding an appropriate spot to anchor the egg mass to the substrate using a mucous thread.

Like many snails, this species is hermaphroditic. Each animal has functioning male and female organs but they require a second individual for fertilization. Several snails will cluster together to mate, and once mated all individuals will lay eggs.

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