FNZ 7 - Cryptostigmata (Arachnida: Acari) - Introduction
Luxton, M 1985. Cryptostigmata (Arachnida: Acari) - a concise review. Fauna of New Zealand 7, 112 pages.
(
ISSN 0111-5383 (print),
;
no.
07.
ISBN 0-477-06762-X (print),
).
Published 08 Dec 1985
ZooBank: http://zoobank.org/References/98C34746-C9D1-4CD1-8FD4-1115A3FAAFAB
Introduction
The number of cryptostigmatid (= oribatid) species known from New Zealand has increased by more than 80%in the past 15-20 years, bringing the number to 366, distributed between 160 genera and 58 families. The list here presented (which includes records from Macquarie, Campbell, Auckland, and Chatham islands) is organised systematically, with keys to all species. The classification used is founded on that of Balogh (1972), with some alterations and additions. The higher classification follows that of Johnston (1982).
The first indigenous species to be described, Crotonia obtecta, was thought by its discoverer (Pickard-Cambridge 1875) to be a phalangid. Although the status of this species has been confirmed from the type specimen (Ramsay & Luxton 1967), no further records of it are known.
The next species to appear in the literature was 'Leiosoma' longipilis, described by Moniez (1894) from collections made in nests of an ant of the genus Monomoria by Smith (1895). This species was recorded in the lists of Lamb (1952) and Spain & Luxton (1971) as Liacarus longipilis, because Liacarus is a senior synonym of Leiosoma. However, the species is quite impossible to identify adequately from Moniez's description, and it has accordingly been omitted from the present work. Hammer (1967), with some justification, suggested that it might be a species of Pseudoceratoppia, and in my view it is probably synonymous with P. sexsetosa Hammer. However, this cannot be confirmed unless Smith's specimens are located.
Michael (1908) described a few cryptostigmatid mites collected from New Zealand, but it was not until the second half of this century that study of the group in New Zealand began properly to develop. Several workers have been responsible (Dalenius, Luxton, Ramsay, Spain, Wallwork, Woolley), but Marie Hammer is truly the doyenne of the subject for New Zealand.
Cryptostigmatids are an ancient group of arachnids with an evolutionary history extending back at least to the lower Jurassic period (Hammer & Wallwork 1979, Wallwork 1979). It has been postulated that the cosmopolitan genera inhabited the supercontinent of Pangaea before its break-up. Those genera of the southern continents which are absent from the northern are thought to have evolved during the time when the southern continents were united as Godwanaland (Hammer & Wallwork 1979, Wallwork 1979). The more localised cryptostigmatid distribution patterns are shown by those forms which have evolved since the land masses attained their present positions (Wallwork 1979), and especially in those locations which are geographically remote. This is clearly evident in New Zealand, where there is a high degree of generic and specific endemism (Hammer & Wallwork 1979). One-third of New Zealand's cryptostigmatid genera have not been reported from elsewhere (Hammer & Wallwork 1979), and 82% of the species are considered to be endemic (Hammer 1968).
The closest links appear to be with South America: 5.5% of the species are known only from these two regions, and 11% of their joint total cryptostigmatid faunas are held in common. Several of these genera have speciated in the subantarctic islands, which suggests the possibility of a previous faunal continuity between New Zealand and South America via Antarctica (Hammer 1968, Hammer & Wallwork 1979). New Zealand has few cryptostigmatid species in common with the islands of the Pacific or with Australia. This suggests that there has been little migration of cryptostigmatids to or from the nearer northern land masses through the agency of air currents or oceanic flotsam (Hammer 1982), or via a previous land connection. Some cryptostigmatids have undoubtedly been introduced to New Zealand through man's activities, although Hammer & Wallwork (1979) list only six possible introductions from Europe.
In New Zealand, mites are by far the most numerous arthropods in the soils of forests (McColl 1974, 1975) and grasslands (Manson 1959, McMillan 1969, Adams 1971, Luxton 1982b), and cryptostigmatids are usually the most abundant (McMillan 1969, Adams 1971, Luxton 1982b). Taxonomic difficulties have prevented the proper development of studies in cryptostigmatid community ecology, but pasture sites are reported to contain between 10 and 16 species (McMillan 1969, Adams 1971, Luxton 1982d, 1983b), and natural peat sites between 16 and 22 species (Luxton 1982c, 1983a). Study of cryptostigmatid mites in these grassland ecosystems should be an economic priority, since Ramsay (1966a) reported that 2-6% of the combined populations of two pasture species alone were infected with cysticercoids of the sheep tapeworm Monieza expansa.
Cryptostigmatids also abound in the above-ground vegetation, the community in this zone largely differing from that of the soil layer. Spain & Harrison (1968) found 18 species associated with the foliage of Olearia colensoi, and Hammer (1967, 1968) recorded 10 species from tree foliage. Furthermore, although cryptostigmatids are air-breathing organisms they are not always strictly terrestrial. For example, in New Zealand 16 species have been recorded from a restiad peat substrate where the water table is always at or near the surface (Luxton 1982c), and 4 species have been described from the marine littoral zone living in algae and rock crevices, amongst barnacles, or in salt-marsh soil (Luxton 1967, 1984).
Cryptostigmata are the only group of mites in which diversity has been achieved in the absence of parasitism (Johnston 1982). Most species (panphytophages) feed on both microbes and the dead remains of higher plants, but some (macrophytophages) prefer to eat dead higher plant material alone, and others (microphytophages) subsist solely on a microbial diet. There have been only occasional reports of carnivory or herbivory.
Reproduction is frequently sexual, the females taking up stalked spermatophores placed by males on the substrate; but many species are parthenogenetic. There are 4 postembryonic developmental stages (1 larval, 3 nymphal) preceding the adult stage, and the juvenile stages are usually quite unlike the adult morphologically. Development times are modified by prevailing temperatures, but in the field are usually long (1 or more years from egg to adult). Each moult is prefaced by a pre-ecdysial resting stage during which the juvenile remains immobile for long periods; this may take up to one-third of the total development time. Usually eggs are laid, but some cryptostigmatids are viviparous.
Cryptostigmatid mites are the most successful of all soil arthropods. They have achieved an astonishing diversity in New Zealand, and deserve to be more widely studied both for their own sake and for the importance of the role they play in soil formation and as vectors of parasites. This contribution is a first attempt at consolidating the literature, and I hope it may encourage further developments in the study of the marvellous mite fauna of this interesting region.