Diplura

Synonyms: Dicellura, Entotrophi, Entognatha Common name: diplurans

Elongate apterygotes; head with long many-segmented antennae, compound eyes, and ocelli absent, mouthparts entognathous; thoracic segments distinct, legs with unsegmented tarsus; abdomen 10-segmented, most pregenital segments with styli, eversible vesicles on some abdominal segments, cerci present as either long multiannulate or forcepslike structures, gonopore between segments 8 and 9.

More than 800 species of this widely distributed, though mainly tropical or subtropical, order have been described. Most holarctic forms belong to the family Campodeidae, including the 11 British species. Just over 60 species have been described from North America, and about 30 from Australia.

Structure

In general form Diplura (Figure 5.3) resemble Thysanura but differ in being entognathous and lacking a median process on the last abdominal segment. Most species are a few millimeters long, but a few may reach almost 60 mm. The roundish or oval head carries the multisegmented antennae, whose flagellar segments (except the most distal) are provided with muscles. The reduced biting mouthparts occupy a pouch on the ventral surface. The six identical legs have an unsegmented tarsus. Two to four lateral spiracles occur on the thorax. Ten abdominal segments are distinguishable. The sterna of segments 2-7 bear styli, and eversible vesicles occur on a varied number of segments. The conspicuous cerci vary in structure and are an important taxonomic feature. In most Diplura (but not Campodeidae, which have none) there are seven pairs of abdominal spiracles.

FIGURE 5.3. Diplura. (A) Campodea sp. (Campodeidae); (B) Anajapyx vesiculosus (Anajapygidae); and (C) Heterojapyx sp. (Heterojapygidae). [From A. D. Imms, 1957, A General Textbook of Entomology, 9th ed. (revised by O. W. Richards and R. G. Davies), Methuen and Co.]

As in Protura, Malpighian tubules are represented usually by a varied number of papillae at the junction of the midgut and hindgut. The tracheal system is developed to a varied extent. Tracheae leading from one spiracle never anastomose with those from other spiracles, and theylack cuticular supporting ringscharacteristicofinsectan tracheae. The nervous system is not specialized, the ventral nerve cord containing eight (Japygidae) or seven (other Diplura) abdominal ganglia. The reproductive system is greatly varied within the Diplura, although in all species the germaria are apical. In Japyx (Japygidae) there are seven pairs of segmentally arranged ovarioles, in Anajapyx (Anajapygidae) two, and in Campodea (Campodeidae) one. One or two pairs of testes occur in the male.

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