INVERTEBRATE ZOOLOGY - H. I. Shcherbak - 2008

KINGDOM MULTICELLULAR ANIMALS (METAZOA)

SUBKINGDOM EUMETAZOA

SECTION TRIPLOBLASTICA, OR BILATERIA

SUBSECTION ECDYSOZOA

PHYLUM ARTHROPODA

SUBPHYLUM TRACHEATA

This subphylum comprises the vast majority of terrestrial animals adapted to life on land and atmospheric breathing via tracheae. A small number of species inhabit aquatic environments, but these are secondarily aquatic animals that still breathe atmospheric air.

The body is divided into a HEAD and a multi-segmented trunk (in myriapods), or a head, a three-segmented Thorax, and a segmented abdomen (in insects). The appendages are uniramous.

The head of tracheates consists of a fused acron and several segments (recently considered to be six) and bears a single pair of antennae, a pair of mandibles, and one or, most commonly, two pairs of maxillae of varying Structure. Eyes are also located on the head (sometimes they are absent).

The trunk can be multi-segmented and more or less homonomous (in myriapods) or divided into a three-segmented thorax and an abdomen (in insects and entognaths).

The Digestive System of tracheates is characterized by the presence of Salivary Glands and the absence of a midgut hepatic or digestive gland. The excretory Organs are represented by Malpighian tubules—long, blindly ending tubes of ectodermal origin that empty into the gut at the junction of the Midgut and Hindgut. Some groups retain maxillary glands similar to those of crustaceans.

The respiratory organs are tracheae, which are fine, branching tubules of ectodermal origin formed as deep invaginations of the integument. They open to the outside through paired openings called spiracles or stigmata, while their finest terminal branches envelop all Internal Organs, transporting oxygen to them.

Tracheates are dioecious. Fertilization is spermatophoric or internal. Development typically occurs with metamorphosis and is predominantly epimorphic, though occasionally anamorphic (in some myriapods and entognaths).

An important feature of tracheates is their suite of adaptations for terrestrial life: an impermeable cuticle; tracheal organs for air breathing; Malpighian tubules as excretory and osmoregulatory organs that conserve Water within the body; uric acid as the insoluble nitrogenous waste product; and The formation of extra egg membranes. Cuticular impermeability is achieved in two ways: through the densification and thickening of the cuticle, as in millipedes, or through the formation of a waterproof epicuticle layer, as in centipedes and higher insects.

The subphylum Tracheata includes two superclasses.