Echiura - spoon worms

Description

Unsegmented marine worms with a short muscular body and a non-retractile proboscis, which may be simple or bifid. The mouth is located at the base of the proboscis and the anus is at the posterior end. The gut is long and highly coiled, but the thick muscular body wall obscures internal anatomy unless a dissection is made. One pair of chaetae typically occur ventrally immediatedly posterior to the mouth; 1-2 rings of chaetae may also encircle the anus.

Comments

Echiurans are marine worms occurring from shallow waters to great depths; several species are estuarine. They are perhaps most likely to be found in muddy environments, although some species are known from seagrass turfs and from under rocks. About 130 species of echiurans are known world wide, with about ... known from Australian waters. Members of the genus Echiura are found on coral reefs, where the green bifid proboscis is often seen during night dives.

Molecular evidence that echiurans may be highly derived members of the Annelida is the subject of recent debate (McHugh, 1997; Siddall et al., 1998).

Identification of Echiura usually requires dissection and care retaining the fragile non-retractile proboscis. Members of the family Bonelliidae display strong sexual dimorphism, but males are minute and occur on or in the females. Stephen & Edmonds (1972) review the systematics of the Echiura world wide, and Edmonds (2000) is an updated family-level review of the Australian fauna. Thirteen species are known from Australia; only 3 of these occur in southern Australia and these are described in Edmonds (1982). Edgar (2000) has a photograph of the most common southern Australian species, the bright green Metabonellia haswelli.

References

Bisewar, R. 1984. A key to the species of Anelassorhynchus (Echiura) with a description of a new species from the east coast of South Africa. South African Journal of Zoology 19, 16-21.

Dartnall, AJ. 1970. A new species of Bonellia from northern Tasmania. Proceedings of the Royal Society of Tasmania 104, 69-71.

Dattagupta, AK. 1976. Classification above the generic level in echiurans. In Rice, ME and Todorivic, M (eds). Proceedings of the International Symposium on the Biology of the Sipuncula and Echiura, Kotor, 1970. Naucno Delo, Beograd, pp. 111-118.

Dawydoff, C. 1959. Classe des Echiuriens (Echiurida de Blainville Gephyrea armata de Quatrefages, 1847). In Grassè, P-P (ed). Traitè de Zoologie. Anatomie, Systèmatique, Biologie. Masson et Cie, Paris, pp. 855-907.

Edgar, GJ. 2000. Australian Marine Life. Reed, Kew, Victoria.

Edmonds, SJ. 1960. Some Australian echiuroids (Echiuroidea). Transactions of the Royal Society of South Australia 83, 89-98.

Edmonds, SJ. 1966. Port Phillip Survey 1957-1963: Sipunculoidea and Echiuroidea. Memoirs of the National Museum of Victoria 27, 175-178.

Edmonds, SJ. 1982. Echiurans (Phylum Echiura). In Shepherd, SA and Thomas, IM (eds). Marine Invertebrates of Southern Australia Part 1. Handbooks Committee of the South Australian Government, Adelaide, pp. 312-318.

Edmonds, SJ. 1987. Echiurans from Australia (Echiura). Records of the South Australian Museum 32, 119-138.

Edmonds, SJ. 2000. Phylum Echiura. In Beesley, PL, Ross, GJB and Glasby, CJ (eds). Polychaetes and Allies: the Southern Synthesis. CSIRO Publishing, Melbourne, pp. 353-374.

Knox, GA. 1957. Urechis novae-zealandiae (Dendy): a New Zealand echiuroid. Transactions of the Royal Society of New Zealand 85, 141-148.

McHugh, D. 1997. Molecular evidence that echiurans and pogonophorans are derived annelids. Proceedings of the National Academy of Sciences of USA 94, 8006-8009.

Monro, CCA. 1931. Polychaeta, Oligochaeta, Echiuroidea and Sipunculoidea. Scientific Reports of the Great Barrier Reef Expedition 4, 1-37.

Nielsen, BJ. 1963. Description of a new species of Bonellia (Echiuroidea, Annelida) from Victoria. Proceedings of the Royal Society of Victoria 76, 61-67, pl.XIV.

Siddall, ME, Fitzhugh, K and Coates, KA. 1998. Problems Determining the Phylogenetic Position of Echiurans and Pogonophorans with Limited Data. Cladistics 14, 401.

Stephen, AC and Edmonds, SJ. 1972. The Phyla Sipuncula and Echiura. Trustees of the British Museum (Natural History), London.