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An inner cellular layer which lies beneath the chitinous cuticle of arthropods, annelids, and some other invertebrates.

Any air-breathing arthropod, as a spider or scorpion.

One of the classes of Arthropoda, including those that have one pair of antennæ, three pairs of mouth organs, and breathe air by means of tracheæ, opening by spiracles along the sides of the body. In this sense it includes the Hexapoda, or six-legged insects and the Myriapoda, with numerous legs. See Insect, n.…

of ciliated disks. By some zoölogists it is thought to be like the ancestral form of the Arthropoda.

A class of air-breathing Arthropoda; -- called also Protracheata, and Onychophora.

One of the lower or outer jaws of arthropods.

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 median elevation behind the mouth in the arthropods.

Any of several arthropods erroneously supposed to kill live stock, in the southern United States, by stinging or by being swallowed; as:

A class, or subclass, of arthropods, related to the hexapod insects, from which they differ in having the body made up of numerous similar segments, nearly all of which bear true jointed legs. They have one pair of antennæ, three pairs of mouth organs, and numerous trachaæ, similar to those of true insects. The larvæ,…

A genus of lowly organized arthropods, found in South Africa, Australia, and tropical America. It constitutes the order Malacopoda.

The anterior of the body of an animal, as of a cephalopod; the thorax of an arthropod.

One of the primary, or first-formed, segments of an embryonic arthropod.

A class of marine arthropods in which the body is small and thin, and the eight legs usually very long; -- called also Pantopoda.

One of the facets of a compound eye of any arthropod.

The sternum of an arthropod somite.

The ventral part of any one of the somites of an arthropod.

One of the external openings of the tracheæ of insects, myriapods, and other arthropods; a spiracle.

The primitive mouth and esophagus of the embryo of annelids and arthropods.

ubesophageal ganglion (Zoöl.), a large special ganglion situated beneath the esophagus of arthropods, annelids, and some other invertebrates.