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but all lack Malpighian tubules and most have paired labial nephridia that empty into the ventral groove at the base of the labium. One universal and unique feature is the ventral tube or collophore (Fig. 2)—a distally weakly paired projection from the first abdominal segment with membranous, sometimes eversible, distal margins. Probable functions include imbibition, excretion, respiration, and adhesion to smooth surface. Collembolan mouthparts are said to be entognathous, being concealed by the head capsule, and typically adapted for chewing. The mandible usually has apical teeth and a molar

FIGURE 2 Typical Collembola anatomy.

FIGURE 3 Collembolan mouthparts. (A) typical mandible and (B) maxilla; (C) reduced mandible and (D) maxilla of Cyphoderidae; (E) piercing and sucking mandible and (F) maxilla of Neanura. (G—I) Various mandibles of Neanuridae and (J-L) various maxillae of Neanuridae.

FIGURE 2 Typical Collembola anatomy.

FIGURE 3 Collembolan mouthparts. (A) typical mandible and (B) maxilla; (C) reduced mandible and (D) maxilla of Cyphoderidae; (E) piercing and sucking mandible and (F) maxilla of Neanura. (G—I) Various mandibles of Neanuridae and (J-L) various maxillae of Neanuridae.

plate, and the maxilla varies greatly and bears a number of complex lamellae.

In some Neanuridae and a few other groups, the mouthparts are simplified and the mandible may be lost (in connection with adaptation for specialized, including liquid, diets). In other Neanuridae the mandibles and maxillae show an inexplicable complexity (Fig. 3) and diversity of form equal to that seen in any other order of insects. The mouth opening is connected to the anterior surface of the ventral tube by a ventral groove through which fluids may flow.

Collembola are equipped maximally with 8 + 8 ommatidia but often have a supplementary light sensory organ between the antennae on the dorsum of the head. A few Collembola possess rudimentary trachea; however, respiration is normally through their thin cuticle and the membranous surface of the ventral tube. The reproductive system consists of paired ovaries or testes opening on the venter on the fifth abdominal segment. Collembolan legs consist of one or two apparent subcoxal segments, a coxa, femur, trochanter, fused tibiotarsus, and distal, normally four bladed, unguis. An opposable smaller lamellate unguiculus is usually present.

Most Collembola have a forked ventral jumping apparatus or furcula on the fourth abdominal segment, consisting of a single basal manubrium and paired distal dentes and mucrones. It is held in place by the latch-like tenaculum on the third abdominal segment. When the tenaculum releases, the furcula catapults the animal, as much as 10 cm. All Collembola are covered with setae but their number, size, and structure vary greatly from group to group. The cuticle of Collembola is extremely varied and often has elaborate surface structures.

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