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The prostomium is bilobed or rounded, and the peristomium is reduced to lips around the mouth. Paired lateral antennae are present in most taxa, and a median antenna is present in many taxa. The ventral palps are fused to the first segment and are tapering without articulations. Nuchal organs are present. The longitudinal muscles are grouped into bundles, and segmentation is distinct. The first segment curves around the prostomium, and usually has very small biramous parapodia, with the neuropodia fused to the lower side of the head, and two pairs of tentacular cirri. The parapodial rami are distinct, and the neuropodia are usually longer than the notopodia in all segments; sometimes the notopodia are very short with few chaetae. Dorsal cirri and elytra occur on alternate segments, at least anteriorly; the posterior end may or may not be covered by elytra. Ventral cirri are present. Branchiae are absent as are epidermal papillae. A pair of pygidial cirri is present. Lateral organs and dorsal cirrus organs have not been observed. The buccal organ is an axial, muscular eversible pharynx with terminal papillae and two pairs of dorso-ventral jaws. A gular membrane is absent, and the gut has segmentally arranged side-branches (caeca). Mixonephridia, are present in many segments. The circulatory system is closed and a heart body is absent. Aciculae are present. Chaetae occur as variously ornamented capillaries and spines.

The above definition is taken from Hutchings (2000), which in turn is based on that given by Fauchald & Rouse (1997).

Identification tips

Recognising the family
Polynoids are the most speciose and widespread of the 6 families known as scale worms because they have two dorsal rows of scales (also known as elytrae). Many species are have short-bodies almost entirely covered by elytrae, which may be ornamented or distinctively coloured, especially when live. Their prostomial (head) morphology is varied, with different groups having different arrangements of the numerous prostomial appendages. Many polynoids have relatively few body segments and a fixed number of elytrae. Polynoids possess two pairs of jaws on an eversible muscular pharynx.

Polynoids are most likely to be confused with one of the other families that also have dorsal rows of scales. The quick guide to scale worms should help separate these 6 families.

Distinguishing species
Characters important for distinguishing polynoid species include prostomial appendages and morphology, ornamentation of prostomial and parapodial appendages, the number of elytrae, their form and the segments on which they occur, and chaetal morphology. Live or freshly collected material from a local area can often be efficiently sorted to provisional species groups relying on the ornamentation and colour patterns of the elytrae. Providing names for these provisional taxa may not be so easy.


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