Description

 Hediste diversicolor is one of the commonest intertidal polychaetes in estuaries. Its body appears flattened with a prominent dorsal blood vessel. Adults may reach 6-12 cm in length and consist of between 90-120 chaetae bearing segments (chaetigers). Appendages on the head are conspicuous consisting of two antennae, and two palps, and four pairs of tentacles. The paired parapodia have dorsal and ventral chaetae and are used for crawling and swimming. The colour of Hediste diversicolor varies. Mature worms become a brighter green approaching and during spawning, otherwise specimens appear to be a reddish orange or brown. There has been considerable controversy over the name to be applied to this species and Nereis diversicolor is used by many authors.The form and distribution of paragnaths on the pharynx can be very useful in identification and Kinberg (1866, cited in Chambers & Garwood, 1992) assigned roman numerals to eight different areas of the pharynx that bear paragnaths. However, the number of paragnaths can vary considerably both within and between populations and this variation is thought to be a result of habitat and feeding preferences (Barnes & Head, 1977).
See Chambers & Garwood (1992) for further description and detail on identification.