Key to Australian Freshwater and Terrestrial Invertebrates

Phylum Arthropoda
Subphylum Chelicerata
Class Arachnida
Order Palpigradi

Common name: palpigrades

Overview

Palpigrades are small pale and eyeless arachnids, less than 1 mm in length. They can be recognised by the presence of an elongate tail-like structure (flagellum) that makes them appear superficially like scorpions, however it is fragile and frequently breaks off. The flagellum does not bear a sting, as is characteristic of the telson (tail) of true scorpions. The pedipalps of palpigrades are leg-like and the first pair of legs are slightly elongated.

Distribution and diversity

Palpigrades are one of the small arachnid orders with only about 80 species recognized worldwide. There are three species from one genus recorded from Australia, but only one is indigenous and is restricted to the subterranean environments of the Yilgarn region of Western Australia. A fourth, possibly endemic, species is known from the Kimberley, Western Australia. The other two species have been introduced since European settlement and have been occasionally found in urban or disturbed environments around Adelaide, Perth and Brisbane.

Life cycle

Very little is known about the reproductive biology of these arachnids except that they lay only a few relatively large eggs at a time. Mating does not appear to have been observed. Juveniles are smaller than adults, but otherwise look the same, and moult several times before maturity.

Feeding

Palpigrades are predators and capture very small soft-bodied invertebrates with their pedipalps. Prey is partially digested pre-orally after the chelicerae cut a hole in the cuticle before digestive enzymes are introduced. The liquefied contents are then sucked out.

Ecology

They inhabit moist microhabitats and occur in damp soil, leaf litter and under rocks and logs, in caves and semi-aquatic interstitial environments. When present, they may be important predators of detritus food-web fauna, however their ecological significance has not been examined. They are not known to have any economic significance.