Subfamily Naidinae Ehrenberg, 1828

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Subfamily Naidinae Ehrenberg, 1828

Compiler and date details

Adrian M. Pinder

Naididae Ehrenberg, 1828.
Type genus:
Nais Müller, 1773.

Brinkhurst, R.O. 1985. The generic and subfamilial classification of the Naididae (Annelida, Oligochaeta). Proceedings of the Biological Society of Washington 98: 470-475 [470]
Nemec, A. F.L. & Brinkhurst, R.O. 1987. A comparison of methodological approaches to the subfamilial classification of the Naididae. Canadian Journal of Zoology 65: 691-707 [706]

Introduction

Mostly small worms, some only a few millimeters long, naidids are distinguished by the anterior position (segments 4 and 5, 5 and 6 or 7 and 8) of the genital organs and dorsal chaetae (generally thin hairs and fine needle-like chaetae with variously shaped tips) that are distinctly different from those of ventral bundles (forked with those of anterior segments often longer). Naidids are closely related to tubificids, in fact there are proposals to included these worms in the Tubificidae as they are believed to be descended from a tubificid lineage (Erséus 2002). Taxonomic arrangement of the family was established by works such as Sperber (1948), Brinkhurst (1985) and Nemec & Brinkhurst (1987).

The more than 100 described species are placed in 22 genera, of which 11 are represented in Australia by 38 species (Pinder 2001). This is fewer genera and species than are present on other continents and Tasmania appears to have surprisingly few species compared to the mainland of Australia. However, such apparently low richness may be a result of insufficient collecting in both cases. Most species present in Australia are cosmopolitan, although two species are endemic and other endemic species are likely to be revealed. The endemic species are 1) Dero (Allodero) litoria, a species that inhabits the ureters of the Green Tree Frog (Litoria caerulea) and possibly other frogs and 2) Slavina proceriseta, a stream-dwelling species from south-eastern Australia (Pinder & Brinkhurst 1998; Pinder et al. 1998). Within Australia, some genera, such as Dero, Branchiodrilus and Allonais, are more likely to be found in the tropics or arid areas whereas others, such as some Nais and Pristina, appear to be more common in temperate regions (Pinder 2001). Pristina longiseta is particularly widespread and common, occurring in habitats as diverse as intermittent arid-zone rivers, coastal dystrophic swA.M.P.s and streams in caves.

While most other oligochaetes are blind sediment dwellers, many naidids crawl or even swim above the sediment and some have eye spots. Naidids such as Nais and Pristina feed on bacteria, periphyton on plants and lithophyton on stony surfaces. One species, Slavina appendiculata, has very long hairs on one segment and uses these to sweep food particles towards the mouth. Chaetogaster, represented in Australia by three species, is characterised by a mouth, pharynx and chaetae modified for preying on invertebrates, including other worms; and one of these species, C. limnaei, inhabits the mantle cavity of a range of molluscs. Most members of the genus Dero, which have small gills on the anal segment, are sediment dwellers, constructing tubes of silt that enable them to protrude the gill chamber into the water column to feed on sediment and detritus. Exceptions to this are species of Dero subgenus Allodero, which are commensal on frogs and have reduced gills. Branchiodrilus hortensi has filamentous gills along the length of its body. Naidid reproduction is often by asexual fission (regeneration of new head and tail ends in mid-body before separation of two new individuals) or fragmentation (new heads and tails formed after the body splits into fragments), so that worms with genitalia are rare. For this reason species descriptions and identification of specimens is often reliant on chaetal morphology, leading to problems in both endeavours.

Naidids commonly occur in lakes (mostly the litoral margins), swA.M.P.s and flowing water (especially stony or vegetated reaches) but occasionally also in more unusual habitats such as water-filled tree hollows. Paranais, represented by two species in Australia (P. litoralis and P. frici), inhabit the marine litoral or mildly saline inland wetlands, including estuaries. Recently, some semi-terrestrial Pristina that inhabit rainforest floors were described from South America (Collado & Schmelz 2001) and Stout found Pristina jenkinae (as P. taita) in forest litter in New Zealand.

Database Notes

The Naididae and Tubificidae are generally considered to form a monopyletic grouping and there have been various suggestions in the literature that these families will be merged sooner or later.

Diagnosis

Testes and spermathecae in IV, V or VII. Ducts feeding sperm, often via an atrium with prostate tissue, to pores on the segment after the testes segment, which also contains the ovaries. Penes absent. Asexual reproduction by fission or fragmentation in many species. Proboscis or eyes present in some species. Dorsal chaetae absent in first few segments in most species (except for Pristina). Dorsal chaetae normally include 1 to a few long hairs and about the same number of short fine 'needle' chaetae which have finely pointed or forked tips and which are normally much smaller and straighter than the sigmoid bifid ventral chaetae. Asexual reproduction by fission or fragmentation common.