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The prostomium is fused to the peristomium. In Owenia, the head is a low, lobed terminal structure; in other taxa, it is rounded frontally, sometimes inflated and bilobed. The peristomium forms a complete ring behind the prostomium. Antennae are absent. The prostomial palps are lobed in Owenia, but may be a pair of grooved palps which emerge dorsally, or are lacking. Nuchal organs have not been observed. The longitudinal muscles are grouped in bundles, and segmentation is present. The first segment is similar to the second segment; in these segments only notopodia are present. Subsequent segments have both notopodia and neuropodia. Notopodia are short, truncated cylinders; the neuropodia are wide with a flattened torus. There are no dorsal or ventral cirri, branchiae or epidermal papillae. Pygidial cirri are usually absent; although some species have multiple pygidial cirri. The buccal organ is eversible and ventral. Gular membranes are absent, and the gut is a straight tube. Segmental organs, termed mixonephridia, open individually on one or a few anterior segments. The circulatory system is closed, and a heart body is lacking. Aciculae are absent. Variously ornamented capillary chaetae are present in the notopodia and very small, unhooded dentate hooks in the neuropodia.

The above description is based on Hutchings (2000), which in turn is based on Fauchald & Rouse (1997).

Identification tips

Until recently one oweniid, Owenia fusiformis was regarded as having a cosmopolitan distribution, however on examination using SEM of the neuropodial uncini has revealed a complex of sibling species and these are also being confirmed using molecular techniques (Michel Bhaud and his co-workers, personal communication). Description of new Australian species in this complex is imminent.

Recognising the family
Members of the Oweniidae have characteristic tubes which are considerable longer than the animal and are composed of shell fragments sand grains which stacked on top of each other (however, species of Phoronis (Phylum Phoronida) in Australia construct very similar tubes).

Distinguishing species
Oweniid genera and species are generally distinguished on the basis of head structures, number of thoracic chaetigers, and shape and dentition of the uncini. Increasingly SEM is being used to distinguish species especially in the genus Owenia, and the structure and dentition of the neurochaetae varies between species. Oweniids often remain intact within their tubes and must be carefully removed for proper examination and identification.


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