INVERTEBRATE ZOOLOGY IN THREE VOLUMES - BOOK 2 - G.I. Shcherbak - 1996

PHYLUM ARTHROPODA

SUBPHYLUM TRACHEATA

CLASS INSECTA, OR ECTOGNATHA

Subclass Pterygota

Ametabolous insects are small (up to 1.5 cm in length) with a spindle-shaped body; about 500 extant species are known. Neither they nor their ancestors ever possessed wings.

The mouthparts are of the chewing type; they feature elongated spindle-shaped antennae and a pair of compound eyes. The legs are walking legs, and the tarsus bears a pair of claws. The abdomen consists of 11 segments and terminates in three long, segmented filaments: a pair of cerci with an unpaired paracercus situated between them. Unsegmented paired appendages known as styli are located on the abdominal segments, serving to support the abdomen during locomotion. Styli are vestigial abdominal limbs.

Fertilization occurs via spermatophores, which the male deposits onto the substrate and the female picks up with her genital appendages. Development follows an archimetabolous pattern lasting from 3 to 24 months. These animals retain The ability to molt in the adult stage.

The subclass Apterygota comprises two orders.

Order Machilida. These animals inhabit rock crevices and live under stones, feeding on Lichens or humus. Styli are present on abdominal segments II–IX (Fig. 159). They are capable of leaping distances up to 15–20 cm.

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Fig. 159. Bristletails: Machilis sp.

Halomachilis maritimus inhabits the coastal rocks of the Southern Coast of Crimea.

Order Lepismatida (or Thysanura). These animals inhabit humid, warm environments and lead a nocturnal lifestyle; consequently, the eyes in many species are reduced or entirely absent. Styli are restricted to abdominal segments VII–IX (Fig. 160).

Fig. 160. Silverfish: Lepisma saccharina

The silverfish (Lepisma saccharina) lives in damp indoor areas (such as bathrooms). It feeds on mold Fungi and various organic components of dust, and may consume starch paste from book bindings, occasionally causing damage. The ant silverfish (Atelura formicaria) lives in ant nests. When one ant regurgitates a drop of food to pass it to another, the silverfish licks up this droplet.