Japanese Bonnet Snail (Phalium/Semicassis bisulcata)

Japanese Bonnet Snail (Phalium/Semicassis bisulcata)

The helmet and bonnet snails (Cassidae) are slow moving hunters which live along sandy coasts in the tropics and subtropics.  Depending on the species (of which tere are approximately 60), these sea snails live anywhere from the intertidal zone to a depth of 100 meters.  During the day they bury themselves in the sand and at night they emerge to hunt their favorite prey—echinoderms (particularly sea urchins).

A Horned Helmet (Cassis cornuta) from the Hawaii coast

A Horned Helmet (Cassis cornuta) from the Hawaii coast

Most of the Cassidae are large snails with big mantles and heavy, muscular foot. They see by means of two eyes located at the base of a single pair of head tentacles and they use an extensible tube for smelling.

A helmet snail closes in on a sea urchin (image from wannadivekona.com)

A helmet snail closes in on a sea urchin (image from wannadivekona.com)

When a helmet snail catches a tasty echinoderm, the snail immobilizes its prey by holding the smaller animal within its mighty foot and releasing a paralytic enzyme from its salivary gland (which prevents urchins from using their spikes in self-defense).  The snail has a sharpened radula (an organ which consists of a chitinous tongue-like strip covered with razor sharp teeth) and two proboscis glands which produce a secretion rich in sulfuric acid.  Using the combination of radula and acid, the helmet snail bores a hole in the echinoderm’s armored body and devours the creature from within!

Shells from the Cassidae family (from OuterBanksShells.com)

Shells from the Cassidae family (from OuterBanksShells.com)

The shells of helmet snails are frequently large and beautiful.  Shaped like a heavy helmet, these shells consist of dextral (right sided) coils which whorl outward from a tight spiral spire.  The snails are divided into males and females (unlike many mollusks which are hermaphrodites or swap genders) and the females lay large masses of hundreds of eggs which can either hatch into planktonic free swimmers or into miniature crawling snails—depending on the species.  Some Cassidae are prized by shell-hunters and artisans such as Cypraecassis rufa, a snail from the coast of Southeast Africa which is favored by cameo carvers.

Bullmouth Helmet Shell (Cypraecassis rufa) from the store "Evolution"

Bullmouth Helmet Shell (Cypraecassis rufa) from the store “Evolution”