In some taxa, the lateral claws have been lost and the empodium is claw-like.
The distal tarsal segment in an arthropod usually ends in a tripartite structure, generally consisting of a pair of lateral claws and a median empodium, which may be claw-like or pad-like (=pulvillus).
The distal tarsal segment in primitive arachnids appears to have consisted of three claws, a condition retained, or re-evolved, in some modern forms.
Tardigrades have four or more curved claws at the end of each leg.
Springtails (Collembola) have a single claw (unguis) that is usually opposed to an empodial appendage (unguiculus) with a lamella, resulting in a snipper-like structure.
Pretarsi have three major components: a median element, the empodium, which may be pad-like or claw-like, and a pair of lateral claws. However, the lateral claws may be absent, leaving only a pad-like pulvillus, or they may be highly modified and seeming to be absent.
Tenent hairs rather resemble flat-headed nails and are probably important in balance or traction. They are found on the body, legs, and tarsi of insects, springtails and mites. Among soil microarthropods, some Sarcoptiformes have leg tenent hairs and many Trombidiformes have tenent hairs on the empodium or lateral claws (sometimes lateral claws are replaced by a pair of tenent hairs).
Author: David E. Walter
Content last updated Sept. 2006, unless indicated otherwise
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