Suborder PHREATOICIDEA Stebbing, 1893

Crenoicus harrisoni

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Suborder PHREATOICIDEA Stebbing, 1893

Compiler and date details

April 2011 - Kelly Merrin

Gary C.B. Poore, Brenton Knott, Helen M. Lew Ton & George D.F. Wilson

Introduction

The Phreatoicidea is a group of freshwater and subterranean isopods that occurs in India, South Africa and New Zealand, but is most diverse in Australia. The epigean (surface-living) species are best recognised by their amphipod-like appearance with a narrow body and well-developed pleonal epimera enclosing the pleopods. The fully hypogean (subterranean) species forms lack these features and appear worm-like. A single pair of styliform terminal uropods is characteristic of this isopod suborder.

The group is represented by Carboniferous to Permian marine fossils from the Northern Hemisphere and Triassic freshwater fossils in Australia (Nicholls 1944; Schram 1986). Nicholls (1943, 1944) recognised two families, Amphisopidae (=Amphisopodidae) and Phreatoicidae. Both families are quite heterogeneous, and have poorly defined subfamilies. In this work, Knott's (1975) recommendations for elevating Nicholls' subfamilies names to families are partially employed. Some genera, however, are shifted from their place in either Nicholls' or Knott's scheme. Recent phylogenetic estimates of many or most genera in the suborder (Wilson & Johnson 1999; Wilson & Keable 2001) suggest that some family-level taxa are sufficiently well supported to receive recognition, whereas others have uncertain relationships. As a result, some genera have not been placed in this classificatory scheme. The family Nichollsiidae Tiwari, 1951 is a junior synonym of the Hypsimetopodidae Nicholls, 1943 in the new scheme introduced here. The phreatoicid subfamily Phreatoicinae is restricted to New Zealand taxa, based on the recently revised Phreatoicus typicus Chilton (see Wilson & Fenwick 1999). Therefore, the subfamily for the south-eastern Australian Phreatoicidaeis (provisionally) Mesacanthotelsoninae Nicholls, 1944. This latter subfamily is not well defined, and may be paraphyletic with some of the other subfamilies, possibly the New Zealand Phreatoicinae.

We eliminated the subspecies category in phreatoicidean taxonomy because most subspecies in isopod taxonomy have been based on taxa with diagnosable differences, but with no evidence for introgression between the subspecies. This decision results in a increase in the described species in the suborder. In Australia, however, many species remain undescribed: estimates suggest that the total fauna may exceed 250 species (Wilson & Keable 2001).

Approximately a quarter of the 56 described species of phreatoicideans are subterranean or hypogean forms. Most of the species, except for the semiterrestrial Phreatoicopsis terricola are dependent on permanent ground water. Knott (1986) listed the distribution of many species and discussed their peculiar biology. Banarescu (1990) provided distributions of species in this suborder, but unfortunately uses nomina nuda from an unpublished thesis (Knott 1975).

Database Notes

The entries for this suborder were input by PCBP from 1988, and revised by GDFW in 1998

Diagnosis

Head capsule much deeper than broad, eyes, if present, near anterior margin. Pleonite pleurae, if present (reduced among Hypsimetopodidae), projecting ventrally. Pleotelson vaulted, higher than broad. Pleonite 5 longer than pleonites 1–4. Antennal article 1 absent or reduced to thin ring; article 3 without scale. Mandibular spine row with bifurcate spines adjacent to the lacinia mobilis (variously reduced in several species). Pleopod exopod I uniarticulate, exopods II–V biarticulate. Pleopod with lateral and medial epipods (although variously reduced on anterior pleopods). Uropods robust, styliform, projecting ventrally and posteriorly.