INVERTEBRATE ZOOLOGY IN THREE BOOKS - BOOK 2 - H.Y. Shcherbak - 1996

PHYLUM ARTHROPODA

SUBPHYLUM TRACHEATA

This subphylum comprises the vast majority of animals. They are terrestrial or secondarily aquatic animals that breathe by means of tracheae.

The HEAD consists of the acron and fused segments, bearing a single pair of antennae, a pair of mandibles, and typically one or, more commonly, two pairs of maxillae of various structures. The head also bears eyes (which are sometimes absent).

The trunk may be more or less homonomous (in myriapods) or differentiated into a Thorax and abdomen (in insects and entognathans).

The Digestive System of Tracheata 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 open into the gut at the boundary between the Midgut and Hindgut. In some groups, maxillary glands similar to those of crustaceans are retained.

The respiratory organs are tracheae—thin, branched tubes of ectodermal origin that arise as deep invaginations of the integument. They open externally through paired apertures called spiracles, or stigmata, while their terminal branches envelop all Internal Organs, transporting oxygen to them.

Tracheata are dioecious animals. Fertilization is spermatophoric or internal. Eggs are mostly rich in yolk, and Cleavage is superficial. Development is generally metamorphic, predominantly epimorphic, and occasionally (in some myriapods and entognathans) anamorphic.

Until recently, the subphylum Tracheata was considered to include two classes: Myriapoda (whose body consists of a head and a more or less homonomous trunk with numerous legs) and Insecta (whose body consists of a head, a three-segmented thorax with three pairs of legs, and an abdomen). However, detailed studies of the structural and developmental features of representatives of these classes indicate significant differences between them. Therefore, we recognize six classes within the subphylum Tracheata: Diplopoda, Pauropoda, Symphyla, Entognatha, and Insects, or Ectognatha (Insecta).