Worms, Annelida 413 gi dc t vc (a) (b) dc dc ac (d) vc (c) gi (e) vc (f) Figure Polychaete parapodia (a) Amphinomid; note similar rami (b) Arenicold; note neuropodia modified to a torus and the musculature linking the base of the chaetae to the ventral body wall (c) Paralacydoniid; note unequal rami and the notable presence of aciculae (d) Phyllodocid; note large, foliose dorsal cirrus (e) Chrysopetalid; note that some of the notopodial chaetae are large, flattened paleae covering the dorsum (f) Spionid; note the dorsal flattened gill Modified from Rouse GW and Fauchald K (1997) Cladistics and polychaetes Zoologica Scripta 26(2): 139–204 structures However, some polychaetes lack nuchal organs, and sensory structures closely similar to the nuchal organs are present in sipunculans, so the presence of these sensory organs may be a shared feature of the annelids and the loss among certain annelids may be a secondary phenomenon Ciliated lateral organs are located between the parapodial rami in many polychaetes, they are usually tufts of cilia in a shallow pit, but may form eversible papillae in some taxa Similarly constructed patches of cilia have been reported from a variety of annelids and may form patterns of sensory organs