Key to Australian Freshwater and Terrestrial Invertebrates
Phylum Arthropoda
Subphylum Chelicerata
Class Arachnida
Superorder Parasitiformes
Common names: ticks and mites
Overview
The Parasitiformes are one of the three major chelicerate lineages of mites and also include those known as ticks which are parasites of mammals, birds, and reptiles. Mites and ticks are distinguished from other arachnids by the lack of body segmentation. There is no division of the body into cephalothorax and abdomen. Instead, the mouthparts and associated sensory structures form a discrete anterior structure known as the gnathosoma. All the rest of a mite�s anatomical structures, including legs, central nervous system, ocelli (when present), and reproductive and digestive systems, are all fused into a single unsegmented body called the opisthosoma. The Parasitiformes are diverse in body appearance with ranging from small (> 0.5 mm), flat, smooth mites to large (2-3 mm), rounded, heavily sclerotised species. Sexual dimorphism may occur with differences in the general arrangement of body sclerites, the modification of male legs used in fighting, and male chelicerae used in sperm transfer. Some species are phoretic and are adapted for dispersal on insects with specialised morphological and behavioural adaptations for the particular life cycle stages of its insect host. The blood-feeding parasites of mammals, reptiles and birds are characterised by mouthparts with a large number of backward-directed hooks that are inserted into the host for feeding.
Distribution and diversity
Globally there are over 12,000 described species of parasitiform mites, with estimates up to 100,000 - 200,000 species. There are over 700 species described from Australia, however there are many more undescribed species known.
Life cycle
Males indirectly transfer sperm by producing a spermatophore (sperm packet) which is placed in the female�s genital opening with his legs or specially modified chelicerae. Parthenogenesis (offspring produced from unfertilized eggs) also occurs in some species. Eggs may be laid straight on to their food surfaces, such as plants, or oviposited into the substrate such as soil or particular host tissue. The first free-living stage that hatches from the egg is the larva which has only three pairs of legs. Subsequently, the larva moults again becoming a first instar with four pairs of legs. Typically, several moults occur before it becomes an adult.
Feeding
Ticks have specially adapted mouthparts to feed on fluid (vertebrate blood). Other parasitiform mites consume small particles of food and are predatory on insects, nematodes and other mites, scavengers on dead arthropods, dung, carrion, and other detritus such as hair, skin, feathers and dust in the nests of vertebrates, or feed on plant material, pollen, nectar or fungi.
Ecology
Parasitiform mites occur in a wide range of habitats including soil, litter, plant foliage, dung, carrion, and in the nests of vertebrates. Several species have phoretic associations with insects (e.g. on dung beetles and grasshoppers) for dispersal while others have varying degrees of symbiotic associations with soil insects occurring in their nests and burrows. Like the Acariforms, the Parasitiform mites contain many economically important species. Those that which parasitise domesticated animals and attack humans are among the best-known Parasitiformes, e.g. the paralysis tick Ixodes holocyclus, which can be dangerous to the health of humans and dogs. Many of the active predators in this order have been used for biological control of insect and mite pests.
