Suborder ONISCIDEA Latreille, 1802

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Suborder ONISCIDEA Latreille, 1802

Compiler and date details

April 2011 - Kelly Merrin

Alison J.A. Green, Helen M. Lew Ton & Gary C.B. Poore

Introduction

For many years the Suborder Oniscidea was called Oniscoidea, a name more properly applied to a superfamily. Its members are supralittoral, terrestrial or secondarily aquatic isopods. Most live in damp places on land. They scavenge on dead organic matter, chiefly from plants. Common names are woodlice, slaters, butcher-boys or pillbugs.

The Actaeciidae, Halophilosciidae, Olibrinidae, Scyphacidae, Tylidae and many Ligiidae are halophilic, restricted to the supralittoral zone. Some species not in halophilic families have been found mainly near marine or estuarine coasts, e.g. three species of Cubaris in Tasmania.

Isopods without pleopodal lungs depend entirely on branchial respiration. They are restricted to more humid places than are members of more advanced families in which pleopodal lungs (usually enclosing pseudotracheae) provide true aerial respiration. Some Australian species have been found associated with ants and one species with termites. Isopods from several genera occur in caves, e.g. Styloniscus, Laevophiloscia and Buddelundia. These range from epigenous animals which wander in from outside to truly troglobitic forms. Haloniscus searlei is secondarily aquatic in inland salt water. Schmalfuss (1984) correlated morphology, habitat and behaviour for Oniscidea in general and his paper applies well to Australian terrestrial isopods.

Among the genera of Oniscidea native to Australia, four distributional patterns can be recognised:
(1) World-wide genera, e.g. Tylos and Ligia;
(2) Southern forms, often primitive, most of whose relatives inhabit southern temperate lands, e.g. Styloniscus and Deto;
(3) Isopods whose nearest relatives are mainly in countries north of Australia, e.g. Cubaris. In general, these are more advanced morphologically than southern forms; and
(4) Endemic Australian genera such as Buddelundia.

The fauna also includes several Palaearctic species introduced to Australia. Eight of these were discussed by Green (1978). The systematics, ecology and zoogeography of the Australian fauna as a whole have not been reviewed but the Tasmanian terrestrial isopods were discussed by Green (1974).

One hundred and ninety-one species of Oniscidea (of which 10 can not be confidently placed in a genus and four in a family) have been recorded from Australia. The number of unpublished species seen by A.J.A. Green and/or mentioned in print is at least another 100. Therefore, in total, about 300 species have been found in Australia to date.

The classification followed in this work is that given by Holdich, Lincoln & Ellis (1984). There are two infraorders: Tylomorpha (with one family) and Ligiamorpha (all other families) subdivided to superfamily level as follows.

INFRAORDER LIGIAMORPHA
Section Diplocheta
Section Synocheta
Superfamily Trichoniscoidea (not recorded from Australia)
Superfamily Styloniscoidea
Section Crinocheta
Superfamily Oniscoidea
Superfamily Armadilloidea
INFRAORDER TYLOMORPHA

The analysis of Schmalfuss (1989) proposed that the Tylidae are not the sister-group of all the others. He hypothesised that the oniscideans are better divided into four sections: Diplocheta, Microcheta, Synocheta and Crinocheta, Tylidae being a member of the last of these. This scheme has not found wide acceptance (Brusca & Brusca 1990; Erhard 1995) and was not followed by Martin & Davis (2001). Tabacaru & Danielopol (1996) used a cladistic analysis of morphological characters to show that the Tylomorpha and Ligiamorpha are sister taxa but recognised four groups in the latter. More recently, Erhard (1998) proposed on the basis of cladistic analysis of the anatomy of the pleon that Diplocheta (Ligiidae) is the sister taxon of all others. This is clearly a different interpretation than traditionally applied.

Within section Crinocheta, the traditional division into superfamilies Oniscoidea, without pleopodal lungs, and Armadilloidea, with pleopodal lungs, is becoming blurred. In fact, some families overlap this boundary. Recent research has shown more diversity in pleopodal respiratory structures, and a wider range of morphology, within families than was realized when the classification of Oniscidea was based more on Palaearctic species (e.g. Ferrara et al. 1994; Taiti et al. 1998).

Seventeen families definitely occur in Australia. Four of these, Halophilosciidae, Armadillidiidae, Cylisticidae and Porcellionidae, are represented here by introduced Palaearctic species. Another, Olibrinidae, is known from Australia only by an unidentified species so it does not appear in the Catalogue. A new family may be required for the enigmatic Haloniscus searlei.

The infraorders, sections and superfamilies of Suborder Oniscidea are diagnosed briefly. The arrangement of the families in the rest of the Catalogue follows this plan and is alphabetical within the superfamilies.

Good diagnoses, in English, have been published for only some of the families of Oniscidea which are in Australia. Original diagnoses written by A.J.A. Green are given for most of the families known to occur here. The diagnoses are based mainly on Australian Oniscidea and the exotic species which have been introduced to this country.

More than any other group of Australian Peracarida, the Oniscidea are plagued by nomenclatural and systematic problems. Our Catalogue has solved some of them but for others we have been forced to list species as unplaced. Some of these problems are discussed in the family introductions and in the sections on genera.

In his monograph on Australian Oniscidea, Vandel (1973) transferred species to different genera with little or no supporting evidence. Some arbitrary decisions about these changes have been made. Where Vandel's new placement seems likely to be correct, his move has been accepted, e.g. Oniscus myrmecophilus Baker to Hanoniscus. Where the information available is inadequate, the species has been returned to its former position, e.g. Armadillo brevicornis Budde-Lund withdrawn from Acanthodillo.

Type material of Australian species was tracked by us to several museums in Europe and England during the 1980s and 1990s or derived from the catalogue of Ellis & Lincoln (1975). Our own discoveries about the material of G. Budde-Lund were confirmed and updated with reference to Jeppesen (1999). Curiously, he made no mention of the many types now in the Western Australian Museum; his counts of syntypes in European museums may include the specimens now in WAM. Mattern & Schlegel (2001) and Mattern (2003) assessed molecular data and discussed its implications for phylogenetic relationships.

Other recent work includes that of Judd & Horwitz (2003) who discussed the distribution of species, including several undescribed in south-western Australia; and Schmalfuss & Wolf-Schwenninger (2002) who provided a comprehensive bibliography for Oniscidea. Schmalfuss (2003) listed the world species, 3527 in all at the year 2000, together with references to systematics and many aspects of biology.

Diagnosis

Antenna 1 with 1–3 articles. Pleonites 1–5 usually separate. Pleopods usually adapted for respiration in air, with pleopodal lungs present in some families.