Mollusks & Crustaceans

Mollusks and echinoderms, crustaceans and other marine arthropods.

Confused? See below.

Crustaceans: includes crabs, lobsters, shrimp, crayfish, barnacles, and others.  Crustaceans have an exoskeleton and usually three body segments.  Crustaceans are arthropods related to spiders and insects.
Other Arthropods: such as the horseshoe crab.  Included also are some insects and arachnids that are strictly marine.  Other insects and arachnids can be found here: Insects & Arachnids.
Mollusks: includes squids, octopus, snails, slugs, mussels, clams, oysters, and others.  Mollusks are anatomically diverse, but usually have a shell or mantle, a foot, and a visceral mass containing body organs.  Mollusks are mostly aquatic, though some are terrestrial.
Echinoderms: includes starfish, sea urchins, sea cucumbers, sand dollars, and others.  Echinoderms are all marine organisms–none are terrestrial and none live in freshwater.  Echinoderms have a radial symmetry unusual to bilateral symmetry in most animals.

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