Slide Ghost Crab

Ghost Crab © Harry Purcell

CRUSTACEANS

Crustaceans are the bugs of the sea. There are about 50,000 species of crustaceans on our planet. For scale, there are about 6,000 different kinds of mammals and about 10,000 species of reptiles. It is a huge and successful group within the phyla of arthropods that also includes the insects and spiders.

 

The name arthropod means jointed legs and the evolution of these appendages into claws, antennae, and wings has allowed them to occupy nearly every habitat on earth. Crustaceans have 10 jointed legs, some have been modified into claws or swimming paddles. Their head is fused with their thorax and there is a tail. Some of the best known crustaceans are crabs, shrimps, crawfish, and lobsters – all popular seafood with the tail being the most desirable  Who ever heard of crab tails? Actually, the tail of a crab has been rolled beneath the animal as an adaptation to aid its survival.

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Fiddler Crabs © UF/IFAS

Crustaceans have a protective shell that is layered with chitin – a strong material that is much lighter and easier to carry than a seashell. This allows for increased speed which adds to the creatures’ defense. If you have ever seen a ghost crab run across the beach, you know they are fast.  Watch closely and you will see they raise some of their legs over their heads so they are not making contact with all their legs – increasing their speed. The crustacean’s exoskeleton must be shed several times a year to accommodate the growing animal, a process known as molting. This is a stressful period for any arthropod as it takes time for the new exoskeleton to harden, leaving them vulnerable to predators, including their own kind. It is amazing to see how much larger the animal is once it has removed its old shell – sometimes 30% larger!

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Blue Crab

Barnacles are typically not recognized as crustaceans. When you see a barnacle on a dock or a boat bottom, you see a shell and think mollusk. If you look closer, you will see there are six panels of calcium carbonate fused together like a tent. There are two additional ones that form the “doors” to the inside. And inside, there is a shrimp like sessile creature that attaches itself by its head. It has very long jointed legs that extend out of the doors and sweep the water to filter for food.

 

Unlike the sessile barnacles, most crustaceans are migratory – moving from the open Gulf to estuaries and back each year to breed. Gulf shrimp only breed once and then die as they typically live less than a year.

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Goose-necked Barnacles © Lila Cox

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