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B. Understanding cicadas(Continued)

6. Anatomy

Description of this image follows.

Cicada anatomy showing main body parts (side view). These include the head, the tymbal, the abdomen and the wing.

Cicadas, like other insects, have three main body parts: head, thorax and abdomen. The thorax bears three pairs of legs and (in adults) a double pair of wings. The base of the abdomen below the folded wings bears a pair of sound-producing organs (tymbals).

Cicadas have a similar overall anatomy to the higher insects (Neuropteradelphia) which include true bugs and their relatives (Hemipteroids), and insects which grow from larvae by way of pupae (Endopterygota). These "higher" insects differ from the "lower" winged orders (Orthopteroids and Palaeoptera) in having the legs attached close together below the body, with the intervening hard parts invaginated to form a supporting internal structure (furcasternum). This makes cicadas capable of running rapidly and with great agility, just like beetles and ants. These "higher" insects also have highly efficient wings (Section 6A) with simplified venation. The wings of cicadas and their relatives do not lie flat when retracted, but fold tightly against the body by means of a movable, triangular lobe (clavus) on the hind margin of the front wing.

Unique features important in identification of cicadas, include a spur (meron) on the hind leg base which usually overlaps an enlarged plate (operculum), which in turn covers the base of the abdomen. The tip of the male abdomen consists of two plates, usually interlocking, an upper one (uncus) and a longer one below it (hypandrium). Between these plates is sandwiched the intromittent organ, a more or less rigid tube (theca) with usually an eversible or at least flexible part at the tip (vesica). These parts are occasionally visible, but more frequently they can be observed only with dissection (Section 6D).

Description of this image follows.

Anatomical drawing of the underside of a male cicada. This sketch highlights the significant features that help in the identification of cicadas, including a spur (meron), an enlarged plate (operculum), and a male abdominal plate (hypandrium).




Other anatomical features of cicadas are those common to the order Hemiptera (or Rhynchota) to which they belong, or to its suborder (Homoptera), or to the division of Homoptera called Cicadomorpha which includes the cicada's closest relatives (see Classification (Section 7)).

Cicadas and other Hemiptera differ radically from other insects in their sucking mouthparts (Section 6B) which are both drawn out into a beak (rostrum) and have the two pairs of jaws transformed into elongate probes (stylets) that fit tightly together to form two "soda straw" channels, one for ejecting saliva, and the other for ingesting liquid food. The basal attachments of the stylets are drawn back into the head capsule. In this, they differ radically from other sucking insects such as butterflies and house flies, which have simple tubes that are entirely external and not composed of parts grooved together.

Since cicadas feed entirely on the watery sap of xylem (the plant tissue that transports water from the roots up to the leaves), they ingest more liquid than they need. Their digestive tract is highly modified to filter out excess water as soon as it is swallowed; this water is then passed to the hind gut for rapid excretion. The filter chamber (Section 6C) that performs this important work is characteristic of both cicadas and their modern relatives (Section 5C), the Cicadomorpha.

Cicadas, like other Homoptera (and also grasshoppers) have great differences in the abdomen of the two sexes. Females have a long, sword-shaped egg-laying device (ovipositor) that can cut a slit in a twig so the eggs will be protected until they hatch. Males have instead a short, blunt terminal segment.

The general body parts of the Homoptera are shown from a leafhopper which has a more generalized body plan than in a cicada. Leafhoppers and some other Homoptera have rudimentary vibration-producing structures (tymbals) on the upper sides of the second (II) abdominal segment; these are greatly enlarged in cicadas as sound-producing organs. For other terminology applicable to cicada morphology, see Invertebrate anatomy online: Cicada.

Description of this image follows.

Anatomical drawing showing the general body parts of a leafhopper (side view). These include the head, the prothorax, the rostrum, the mesonotum, the coxa, the mesothorax, the metathorax, the abdomen (separated into nine distinctive segments) and the anal tube (divided into two parts).

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