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A class of Arthropoda, allied to the Crustacea. It includes the trilobites, Eurypteroidea, and Limuloidea. All are extinct except the horseshoe crabs of the last group. See Limulus.

A larval crustacean in a stage following the nauplius, and having about seven pairs of appendages.

A small crustacean with one median eye.

A crustacean larva having three pairs of locomotive organs (corresponding to the antennules, antennæ, and mandibles), a median eye, and little or no segmentation of the body.

A genus of small marine Crustacea, considered the type of a distinct order (Nebaloidea, or Phyllocarida.)

The modern, or true, Crustacea, as distinguished from the Merostomata.

Any crustacean of the genus Remipes.

A compound eye, as of insects and crustaceans.

One of the single eyes forming the compound eyes of crustaceans, insects, and other invertebrates.

The part of the carapace of a crustacean situated behind the cervical groove.

One of the plates which in some Crustacea inclose a cavity wherein the eggs are hatched.

An eyestalk; the organ which bears the compound eyes of decapod Crustacea.

Any species of amphipod crustacean of the genus Orchestia, or family Orchestidæ. See Beach flea, under Beach.

Egg-bearing; -- applied particularly to certain receptacles, as in Crustacea, that retain the eggs after they have been excluded from the formative organs, until they are hatched.

Any one of a tribe of anomuran crustaceans, of which Pagurus is a type; the hermit crab. See Hermit crab, under Hermit.

stinguished from kenogenesis. Sometimes, in zoölogy, the abrupt metamorphosis of insects, crustaceans, etc.

ally, one of the jointed sense organs attached to the mouth organs of insects, arachnids, crustaceans, and annelids; as, the mandibular palpi, maxillary palpi, and labial palpi. The palpi of male spiders serve as sexual organs. Called also palp. See Illust. of Arthrogastra and Orthoptera.

One of the two lobes which form the lower lip, or metastome, of Crustacea.

One of the outer divisions of an endosternite of Crustacea. -- Par`a*phrag"mal, a.

A division of copepod Crustacea, having a sucking mouth, as the lerneans. They are mostly parasites on fishes. Called also Siphonostomata.