Key to Australian Freshwater and Terrestrial Invertebrates
Phylum Arthropoda Subphylum Myriapoda Class Pauropoda
Common names: pauropods, pauropodans
Pauropods are minute soil myriapods of approximately 0.5-1.5 mm in length with 8-11 trunk segments. Some pauropods are more strongly sclerotized and move slowly, while others are pale in colour and are able to run quickly. The tergites are fused in pairs giving the dorsal appearance of fewer segments when viewed from above. Each segment bears a single pair of legs and there are five pairs of long sensory hairs on the trunk. Behind the last trunk segment there is an anal segment that has a posterior anal plate. Characteristics of the plate, such as size, shape and texture, are used to distinguish species. Almost every species can be identified from this plate, even at the first larval stage. The head is poorly developed and directed downward with characteristic branched antennae and small chewing mouthparts. The first set of jaws has curved teeth that look like a comb, while the second pair is joined together to form a flaplike structure. Pauropods have distinctive locomotory pattern characterized by rapid burst of movement and frequent abrupt changes in direction.
Distribution and diversity
The Pauropoda are an obscure and poorly studied group. There are 700 species described worldwide that are grouped in two orders, Hexamerocerata and Tetramerocerata, and five families. The total world fauna is likely to be in the region of 5000 species as many regions and ecosystems are under-collected. The Australian fauna is estimated to comprise at least 1000 species of which only 18 endemic and introduced species are described so far.
Pauropoda have separate sexes, however in some species males have not been observed and these species are thought to be parthenogenetic. Males deposit small spherical sperm-packets in the soil, which the females seek and pick up. Females deposit eggs on the substrate. The egg develops through a short pupoid phase at the end of the embryonic development and before the first larval stage. The larval stages growing through a series of moults that generally resemble adults, apart from a smaller size, fewer number of body segments and different number of setae. First instar larva have three or six pairs of legs, but that number increases with each molt so that adult species may have 9 to 11 pairs of legs.
The food habits of most species are unknown, but some feed on decaying organic matter and mold or suck fluids from fungal hyphae. At least one species is known to eat tiny root hairs on plants.
Pauropoda are associated with soil and litter habitats and can occur under moss and rocks, in decaying wood, or under the bark of decaying logs. They are generally most abundant in moist soils that have high levels of organic matter. Although these animals are not rare, they often have small population sizes with patchy distributions. They are particularly species-rich and abundant in forest soils and have been reported to have several thousand specimens per square meter in wild and agricultural habitats. They inhabit many plant communities and soil types and are most abundant in a zone about 10–20 cm deep. However, though they cannot burrow, they can follow root canals and crevices down to the groundwater surface. Vertical migration can occurs when there are changes in soil moisture and temperature.