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CASSIDAE (Helmets and Bonnets)

Phalium areola (Checkerboard Bonnet)

shells
Photo: Robert Whyte

Cassidae are large or medium size shells characterised by a thickened and recurved outer lip forming a prominent helmet-like rim. There are eighty or more living species in warm waters around the world.

Often washed up on sandy beaches. Helmets feed on echinoderms, including sea urchins, which they crawl onto with the thick skin of the foot providing protection from the spines. They make a hole in the urchin shell with an acidic secretion and by rasping with the radula and suck out the soft parts.

Phalium areola (Checkerboard Bonnet)


Phalium sp
Photo: Robert Whyte

In the Cassidae the columellar callus extends onto the ventral surface and is referred to as the columellar shield. The margin of the columellar shield, which is the edge away from the aperture, may adhere to the ventral surface of the whorl or be free standing, and may be straight, indented, or convex. The shield itself may be smooth or sculptured. Members of this family are renowned for great shell variability, which is particularly evident in two NSW species, Semicassis pyrum and S. labiatum. This has lead to a number of variants being described as species, subspecies and forms, some of which still require investigation to determine their exact relationships. (Beechey, seashellsofnsw.org.au)

Semicassis angasi


Semicassis
Photo: Robert Whyte

Semicassis angasi's shell is light in weight, with whorls rounded. Body whorl smooth, with weak spiral threads on shoulder and spiral grooves at base. Outer lip reflected, toothed along inner edge. Colour white, fawn or pink. Up to 54 mm in length.

Found from the Kimberley, WA, to Sydney, NSW.

Semicassis? A Bonnet? from below


Cassidae
Photo: Robert Whyte

This shell is not a very commonly found one, being rare In NSW and uncommon in Northern Australia.

Cypraecassis rufa (Bullmouth Helmet, Cameo Shell)


Cassidae
Photo: Robert Whyte

Probably not a local shell, this is the famous Bullmouth Helmet or Cameo Shell, a very heavy shell.

Cypraecassis rufa (Bullmouth Helmet, Cameo Shell)


Cassidae
Photo: Robert Whyte

The thick shell is popular for use as a base for cameo carvings. The name means cowrie-like.

Cypraecassis rufa (Bullmouth Helmet, Cameo Shell)


Cassidae
Photo: Robert Whyte

This specimen is a large, presumably old shell. These shells are sold on eBay among other places.