Pedipalp
Pedipalps, the second pair of appendages of the cephalothorax in Arachnida, is homologous with mandibles in Crustacea, and corresponding to the mandibles of insects. The pedipalps are appendages of six segments: the coxae, a single trochanter, the femur, a short patella, the tibia, and the tarsus. The coxae, most frequently have extensions, called maxillae or gnahobases, which function as mouth parts with or without contribution from the coxae of the anterior legs. The limbs themselves may be simple tactile organs outwardly resembling the legs, as in spider, or chelate weapons of great size, as in scorpions. Comparative studies of pedipalpal morphology suggest to me that leg-like pedipalps are primitive in Arachnida. At present, the only reasonable alternative to this view is to assume that xiphosurans reflect the morphology of the primitive arachnid pedipalp and to conclude that this appendage is primitively chelate. Pedipalpchelae are found in several arachnid groups, Ricinulei, Thelyphonida, Scorpiones and Pseudoscorpiones, but the chelae in most of these taxa do not appear to be homologous with those found in Xiphosura. The pedipalps are distinctly raptorial in Amblypygi, Thelyphonida, Schizomida and Opiliones.
Spider pedipalps
Pedipalps of spiders have the same segmentation as the legs, but the tarsus is undivided, and the pretarsus has no lateral claws. A male spider enlarged ends of his pedipalps, the terminal segments of which are elaborated into organs for the transfer of sperm to the sperm receptacles of the female.
Sources
- Discovery Books; 2000; Insects and Spiders; St. Remy Media Inc.; New York; 35
External links
- Close-up view of sperm-laden pedipalps in a mature tarantula
- Several close-up photos of a tarantula creating a sperm web - Brachypelma Vagans (Mexican Red-rump)