Range: Tropical and subtropical marine water

Habitat: Often coral reefs

Size: Less than an inch (2.5 cm) to over 7 inches (18 cm)

Diet: Generally herbivorous algae eaters, some eat sponges and bryozoans

Threats: Large fish and octopuses

Lifespan: Two to ten or more years

Transcript:

Today on Animal Fact Files we’re discussing cowries. There are over 200 living species of these shiny shelled molluscs. You may be familiar with their shells, as they often appear in souvenir shops around the beach, but did you know that the animal inside can fully extend to cover its shell in life? This is why this invertebrates' shell is so shiny! Unlike other mollusks who add layers to their shell from the inside, thus making a shiny interior, cowries add layers to their shell along the outside giving them a smooth surface. Throughout the world, cowrie shells have been used as decor, symbols of fertility, and even money, but there's more to these animals than just their shell.

Cowries are mollusks that live in tropical and subtropical marine waters around the world. They have the most species diversity in the Pacific Ocean. These invertebrates are most often found living in shallow environments on coral reefs, although they also inhabit eelgrass beds, lagoons, and even some deep water places. Generally speaking, cowries with thicker shells can handle environments with more aggressive wave action, and those with thinner shells prefer calmer seas. 

Cowrie shells come in a variety of colors and patterns, however, they often cover these vibrant shells with their more cryptically colored mantle. What's more, some species have mantles with various fleshy projections which can further help to break up their outline and help them blend in. These may also help with respiration. When threatened, a cowry can quickly retract its mantle inside its shell, giving the appearance of rapidly changing color, to startle any wouldbe predators. Their tough shell tends to keep them safe from smaller fish and crustaceans, however cowries do fall prey to octopuses who can drill through their shell and larger fish who simply swallow them whole.

In size, these mollusks range from about an inch (2.5 cm) to over seven inches (18 cm) long in shell length. Their sexes are separated, and females are typically larger than males. This may be to help accommodate egg production and brooding. Unlike many mollusk species, cowries are known to stay with their egg brood until they hatch. This may take anywhere from a week to nearly a month. Larvae hatch and either float through the water column as plankton or emerge more developed and simply crawl along the seafloor. In species that have more developed larvae, the mother often lays her eggs near a source of food, so the babies have easy access to a meal as soon as they hatch.

Many cowrie species are herbivorous. They use a scraping tongue to remove algae from surrounding surfaces. There are some species that eat animals, as well. These tend to go for sponges and bryozoans. Many are nocturnal, seeking out food at night, however some thicker shelled species brave the day and cruise about while the sun's out. It's believed that cowries have a relatively quick development cycle so they can reach adulthood with a protective shell as fast as possible. Something else that separates them from many other mollusk species is that their shell stops growing once they reach their adult size. Depending on the species, they may live for a few years to more than a decade.

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