Little is known about the development of polynoids. A large number of unidentifiable polynoid trochophores and nectochaetes have been described by Nolte (1936) and others. As Thorson (1946) states, Nolte has done little to clear up the confusion that prevails in this group and his 'numerous figures, all more or less incorrect, and accordingly difficult to recognize, merely serve to further obscure our picture'.

A search of the literature with the aid of Hartman (1951) has so farrevealed only one clearly identifiable member of the family whose early larval stages have been described. Sars (1845a, b), making some of the earliest observations on polychaete life histories, described under the name Polynoe cirrata Fab. the early stages of Harmothoe imbricata (L.). Further studies in some detail on this or a closely allied species were made in turn by Miiller (1851), Mclntosh (1900) and Izuka (1912). The certainty of identification of the parent in this case stemmed from the fact that the early stages, with the exception of those studied by Miiller, were not taken in the plankton but were observed attached to the brooding parent after release from it. In this polynoid the eggs are carried in large masses beneath the elytra, and larvae leave the parent as actively swimming trochophores. This method of carrying the young has also been observed in H. imbricata by Saemundsson (1918) in Greenland and by M. Pettibone (personal communication) in Puget Sound. Desor (1857) quotes the observations of Sars on the brooding habit, and describes the release of trochophores by Polynoe squamata (= Lepidonotus squamatus L. ?) on the New England coast.