What Are the Relatives of Pill Bugs?

Cladocera

• Water fleas are members of the order cladocera. They're widespread little crustaceans that grow from .008 to .24 inches long. They have a carapace that opens at the front and the end. The carapace is clear, which allows you to see its internal organs. They have antennae used for feeling and swimming and a tiny primitive eye called an ocellus. The female water flea has a brood chamber between the body wall and the top part of its carapace to carry eggs. Water fleas can reproduce both sexually and through parthenogenesis, where the sperm is not necessary. Water fleas eat algae, detritus and a bacteria and are often used to clean fish tanks of the algae bloom.

Euphausia

• Krill are shrimp-like crustaceans. They are found in huge schools, especially in the Antarctic, and are just about the sole food for the blue whale. They may become as dense as 10,000 krill per cubic meter of water. They can grow from .315 to 2.7 inches long, and the largest krill can be up to 5.51 inches long. They are also bioluminescent, and the light they give off might help them to congregate. There are two species. Entheuphausia amblyops can be found in the southern part of the North Atlantic ocean in water at least 3,280 feet deep. Euphausia superba are found in Antarctica to a depth of 328 feet or less. Both are filter feeders and eat plankton. During the night krill rise to the surface, then return to deeper water during the day. Krill lay as many as 8,000 eggs per brood in the spring and can spawn many times a season.

Paguroidea

• Hermit crabs belong to this family. A hermit crab is a crustacean like the pill bug but doesn't have a hard sell. So it uses the discarded shells of other animals for protection, especially the shells of whelks. As the crab grows it has to find another shell. Hermit crabs have 10 jointed legs. The front two are modified into pincers, and the rear pair are small. They have antennae, two eyes at the end of stalks and a soft abdomen that needs to be kept inside the shells. Hermit crabs are omnivores and scavengers.

Homarus

• Two species of lobster belong to the genus Homarus. The American lobster can be found from the Canadian Maritimes to North Carolina but is most abundant in Maine. The European lobster is harvested in France, Germany, Denmark, Sweden and Norway. They are very similar, with only slight differences in their morphology; the American lobster has more crushing strength in its claws. The American lobster can grow to more than 3 feet long and weigh 40 pounds, but most that are caught are smaller. The female is ready to mate when she's about 5 years old and will lay eggs between one month and two years after mating. She fertilizes them with sperm she has stored. The larger she is, the more eggs she will lay. She carries them beneath her tail for about 10 to 11 months before they hatch.