Family PHREODRILIDAE Beddard, 1891

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Family PHREODRILIDAE Beddard, 1891

Compiler and date details

Adrian M. Pinder

Phreodrilidae Beddard, F.E. 1891. Anatomical description of two new genera of aquatic Oligochaeta. Transactions of the Royal Society of Edinburgh 36: 273-303 [290].
Type genus:
Phreodrilus Beddard, 1891.

Brinkhurst, R.O. 1991. A phylogenetic analysis of the Phreodrilidae (Annelida, Oligochaeta), with a description of a new species. Canadian Journal of Zoology 69: 2031-2040
Pinder, A.M. & Brinkhurst, R.O. 1997. A review of the Phreodrilidae (Annelida: Oligochaeta: Tubificida) of Australia. Invertebrate Taxonomy 11: 443-523

Introduction

This family of mostly aquatic worms had a tortuous early history. Beddard (1891) described the first phreodrilid, Phreodrilus subterraneus, from New Zealand, for which he erected the family Phreodrilidae. The same author later (Beddard 1894) described two more species (now recognised as phreodrilids) but placed them in a new genus of tubificid (Hesperodrilus) and shortly afterwards (Beddard 1895) also placed Phreodrilus with the Tubificidae. A review of the Oligochaeta by Michaelsen (1900) concurred with Beddard's placement of all of these species in the Tubificidae but later (Michaelsen 1903) reinstated the family Phreodrilidae and placed all species in Phreodrilus. Subsequent papers described further new species and two genera, though the latter were also synonymised with Phreodrilus by Brinkhurst (1965) after he failed to find consistent distinguishing characteristics for any of the separate genera. The present phylogenetic classification, with two subfamilies and multiple genera was established following an analysis by Brinkhurst (1991).

The global distribution of the family suggests a Gondwanan origin (Brinkhurst 1965): most species have been described from Australia, with fewer from New Zealand, Africa, South America and southern oceanic islands such as CA.M.P.bell and Kerguelen Islands. Records from equatorial latitudes and arid regions are from high altitude (e.g. in Sri Lanka) or deep lakes (Africa) or groundwater (Africa, Middle East and Australia) (Giani et al. 1995; Martinez-Ansemil et al. 2003; Pinder 2003). A recent record from the very deep Lake Biwa in Japan (P. Martin, pers. comm.) seems anomalous, but another recent record (from Ireland, the first for Europe) almost certainly represents a human-mediated introduction (Gunn et al. 2004).

Fifty species have been described worldwide in seven genera, of which 29 described species in six genera are known from Australia. Many other Australian species are known but not yet described (Pinder 2001). Most phreodrilids have restricted distributions, with 15 described species (and many undescribed) known only from Tasmania, one only from the southern Great Dividing Range and five described (and several undescribed) from south-western Australia. Above the species level, there is little geographic disjunction, except that the species from the Great Dividing Range, Phreodriloides notabilis, has no congeners, and Schizodrilus is known only from two poorly known New Zealand species. Recent unpublished studies have revealed the presence of numerous new phreodrilids in north-western Australian groundwater aquifers and associated springs and one of these was described recently (Pinder 2003). Other undescribed species are known from caves in the south-west. Only two species are currrently known from more than one continent: Insulodrilus lacustris from South America, New Zealand and southern Australia and Antarctodrilus niger from South America, Falkland Islands, South Africa and Tasmania. The former, which is very common in Australia, appears to have quite variable morphology and may represent more than one species, while A. niger is known from very few specimens.

Phreodrilids of surface waters are sediment dwellers, although some have been collected from saturated moss on stream edges of subantarctic islands (Pinder & Brinkhurst 1997) and some mostly undescribed species are known from moss beds of granite outcrops of temperate to semi-arid south-western Australia (Pinder 2003). They also appear to be common inhabitants of caves, springs and groundwater aquifers in southern continents, with some overlap in the species of surface and underground habitats. One species, Astacopsidrilus ostiensis, occurs in estuaries (Pinder & Erséus 2001) but none is known to be truly marine. The two species of Schizodrilus from New Zealand inhabit litter of beech forests (Stout 1958) and three species of Astacopsidrilus from eastern Australia occur on the carapace of crayfish but appear to be commensal detritivores rather than parasites. Very little is known of their biology but judging from gut contents all appear to be detritivores and/or grazers on periphyton. Asexual reproduction (by fragmentation) has been reported for Schizodrilus but other phreodrilids appear to reproduce sexually. An absence of spermathecae in Phreodriloides notabilis suggests autofertilization but this has not been confirmed.

Diagnosis

Aquatic (mostly freshwater) oligochaetes. Ventral chaetae from II, paired and sigmoid with bifid or simple tips, if bifid then usually with upper teeth much shorter and thinner than the lower. Ventral chaetae of XIII (the spermathecal segment) often modified as one or two thin hollow-tipped chaetae, often larger than adjacent somatic chaetae. Dorsal chaetae absent in II, usually present from III, rarely absent in other anterior segments. Each dorsal bundle either with one to many hair chaetae which may be serrate or brush-tipped, or with single or paired sigmoid chaetae which resemble those in ventral bundles. If hairs, then each usually accompanied by a lateral (support) chaeta on each side which do not usually project from the chaetal sacs. Proboscis may be present. Pharynx usually with thickened eversible roof in II and III and pharyngeal glands in several segments between IV and X. Reproduction usually sexual but asexual propagation known in one genus. Thin clitellum normally restricted to XII and XIII. Testes and ovaries paired in XI and XII, respectively. Male pores in XII, female pores within intersegmental furrow 12/13 or ducts plesioporous with pores anteriorly in XIII or coincident with the opening of the spermathecal vestibulae or within the vestibulae. Reproductive organs shifted forward in some taxa where fewer anterior segments regenerate after asexual reproduction. Gonoducts paired. Male ducts lack separate prostate glands. Inner epithelial lining of the atrium thick and glandular in most species, leaving only a narrow lumen. Ciliated vasa deferentia usually thin and usually opening into atria basally or even directly into pseudopenes or ejaculatory ducts. Pendant penes or eversible pseudopenes usually present, but extent of development varies substantially between taxa. Spermathecal pores on XIII, usually within a shallow to deep muscular inversion of the body wall (vestibule). Spermathecal ducts with a narrow lumen and usually with a valve-like structure at the A.M.P.ulla union. The A.M.P.ullae, which may be thin and duct-like anteriorly, usually extend over one or more segments posterior to XIII. Sperm not stored as spermatozeugmata.