Range: Tropical and temperate marine waters throughout the world

Habitat: Sandy bottom shallow seas (though can be found over 1,000 feet (300m) deep)

Size: Average 3 inches (7.6cm) but range from 0.8 to 4.7 inches (2-12cm) long

Diet: Detritus collected from crushed sand particles

Threats: Bristle worms, crabs, and more

Lifespan: Unknown, though related sand dollars can live to be a decade old

Transcript:

Today on Animal Fact Files we’re discussing sea biscuits. No, not the horse. This video focuses on the invertebrates also known as cake urchins that live in the ocean. Sea biscuits are a group of sand dollars that are puffier than their flat, cookie-shaped relatives. In the same way a biscuit is more puffed up than a cookie, the sea biscuit is more puffed up compared to other sand dollars. Sea biscuits are echinoderms like sea stars and sea cucumbers. They’re sea urchins, and they’re part of the sand dollar order, but they stand apart from their relatives with their chunky, biscuity appearance. There are over 400 named sea biscuit species, though not all of these are living today.

Sea biscuits can be found in tropical and subtropical marine waters throughout the world. They are most frequently seen on sandy bottom areas with little vegetation; though some species, specifically the puffier ones, may prefer areas with more foliage. They are most common in shallow waters but can be found deeper than 1,000 feet (300m) below the waves. Some species are flatter than others. These tend to be burrowing types that live under the sand at the bottom of the water column. Their flat body helps them burrow more efficiently. The puffier sea biscuits may not burrow, instead walking along the surface of the sea’s substrate using the spines that surround their body. Like other sea urchins, they can cover themselves in debris like shells and seagrass. They appear in opposite sexes, meaning individuals display either male or female characteristics, and they form large groups which facilitate reproductive success..

Male sea biscuits release sperm into the water column which fertilize the eggs released by females. Though they have peak spawning times, sea biscuits are believed to spawn year round. Eggs hatch into planktonic larvae that eat and grow. They look sort of like tiny jellyfish. It takes about a month for these to settle to the seafloor and continue their journey to adulthood.

Sea biscuits grind up sand particles using the five crushing teeth located inside their mouth. Their jaw is referred to as the Aristotle's Lantern. Food particles are moved to the mouth located on the animal’s underside via tube feet and digested. During this process, sand is expelled from their body. So next time you're at the beach just remember it may have passed through a sea biscuit - or a parrotfish - or both!

Predators to sea biscuits include crabs and bristle worms. Their strong skeleton, called a test, helps keep them protected. The puffier species especially have thickened tests that can be difficult to break open. On average, sea biscuits reach about three inches (7.6cm) in length, so they approximately fit in the palm of a human's hand. They're slightly longer than other sand dollars, giving them a more oval shape compared to their flat, cookie cousins.

For more facts on sea biscuits, check out the links below. Give a thumbs up if you learned something new today. Thank you to our Patrons SpikeSpiegel93, Dad, and everyone else for their support of this channel! And thank you for watching Animal Fact Files!