There are over 30,000 species of crustaceans and over 100,000 species of mollusks. Animals in the crustacean family include crabs, crayfish, shrimp, prawns, lobsters, barnacles, water fleas and wood lice. Animals in the mollusc family include mussels, clams, oysters, scallops, conch, whelk, squid, octopus, chitons, limpets, slugs and cuttlefish. These animals have certain characteristics that set them apart from other aquatic and terrestrial beings. These characteristics include their physical appearance, habitat, feeding techniques and reproduction.
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Crustacea have five pairs of appendages on their heads. Two pairs of these attachments are antennae that are needed to find food and sense changes in temperature. The remaining appendages are used for feeding. These include the mandibles, or jaws, and armlike maxille. A varying number of other appendages are found on the trunks of crustaceans. The most prominent characteristic of a crustacean is its exoskeleton which is a hard skeleton on the outside of its body. Mollusks have a head and mouth, a powerfully built foot, a hump with digestive and breeding organs and many have tissue called a mantle, which it secretes to become its protective shell.
Most crustaceans live in aquatic environments. Some crustacea, such as wood lice and pill bugs, create their habitats on moist land. Crustaceans can also be parasitic and live on other aquatic creatures or even on other crustaceans. Different species of mollusks live in water or on land. They rarely live in desert climates but do survive in arctic and tropical environments. Snails were originally saltwater dwellers but later adapted to live in fresh water and then on land. Some mollusks are parasitic and live on other animals.
Crustacea have several feeding techniques depending on their size and what they consume. Filter feeding is the feeding technique for small crustaceans including small shrimp and copepods. The animal waves small, thin setae, which look like oars, back and forth, creating a water current. Plankton are carried into its filters and then eaten. Larger animals like crabs and lobsters use their maxille to crush and eat food. Mollusks may be herbivores, carnivores, scavengers, filter feeders, deposit feeders, or parasites. Different mollusks may eat plankton, fish, crustaceans, jellyfish, coral animals or other mollusks.
The majority of crustacea are dioecious, meaning they are either male or female, but some, like barnacles, have both sex organs. Fertilised eggs are carried by the female in a brood chamber inside the body or attached externally to one of its appendages. Mollusks are either male or female and reproduce sexually.
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