False cowries are a family of snails which live on, and prey on corals, particularly soft corals and sea fans. These snails are sometimes considered external parasites, as they can attach themselves to soft corals with their molluscan foot, and then slowly devour the coral polyps.
These snails have smooth shiny shells with a long opening which can be shaped like a pear, an egg, cylinder or lance. The shell is often plain white, but can also be reddish or pink. The false cowrie shell is almost completely covered with a colourful mantle (from the latin 'robe' or 'cloak') which secretes the calcium carbonate required for shell growth.
False cowrie mantles can often adopt the colour and pattern of the 'host' coral which they are eating. This provides an excellent camouflage for the snail.
The Common Egg Cowrie has a large, egg shaped shell with a black mantle. The mantle has numerous small white spots which are arranged in very loose circle shapes.
The actual shell (under the mantle) is bright white, smooth and shiny. The edge flaps of the mantle usually completely hide the white shell, however the mantle can be quickly retracted into the shell opening when the cowry is disturbed.
Juveniles have large bulbous white and yellow and reddish speckled fleshy projections, and can often be mistaken for sea slugs.
The Common Egg Cowrie grows to 12 cm in length, but more often observed around 6 cm - 8 cm. The diet includes leathery type soft corals.