Key to Australian Freshwater and Terrestrial Invertebrates
Phylum Annelida
Class Polychaeta
Family Capitellidae
Common names: capitellids
Overview
Capitellids resemble terrestrial earthworms, with a pointed or rounded head lacking appendages and a long cylindrical body. Parapodia are poorly developed and chaetae appear to arise directly from the body wall. They are often reddish in colour and may be tightly coiled on the collecting sieve. Capitellids have more than fifteen segments with a distinct thorax and abdomen, marked by different types of chaetae on the different body regions. They can have absent, one or more pairs of eyes.
Distribution and diversity
Approximately 150 species in nearly 50 general are known globally. The Australian fauna contains approximately 19 described species from 9 genera, but there are over 50 undescribed species known from Australian waters. Four of these species (in two genera) are found in freshwater. The following species are actually regarded as species complexes (a group likely to contain multiple species), but are found in esturine or coastal lagoon environments in Australia: Capitella capitata, Capitellides dispar, Heteromastus filiformis and Heteromastus similis.
Life cycle
For many genera, little is known about copulation or spermatogenesis. There are reports that the males of some species transfer a spermatophore (held in the genital ducts) to the female during copulation. Females spawn a large number of eggs several times, sometimes producing over 1000 young in their lifetime.
Feeding
Capitellids eat micro-organisms adhering to the mud particles, swallowing the mud using an eversible proboscis.
Ecology
Capitellids may be extremely abundant in muddy sediments; some are tolerant of polluted conditions and may be useful as pollution indicators. Some species of capitellids that have been found in contaminated sediments can build up dense populations very quickly, but these populations may then crash. Most species build burrows with simple traces, or which comprise interconnected galleries.
