Spiochaetopterus solitarius (Rioja, 1917) (Polychaeta: Chaetopteridae, originally described in the genus
Phyllochaetopterus) is redescribed from newly collected material from Atlantic populations at the type locality: Santander Bay, northern Spain, and one population in the northwest Mediterranean: Port-Vendres, France.
S. solitarius is compared with Mediterranean material of
S. costarum (Claparède, 1870), with which it was originally confused. None of the examined specimens have the ‘antennae’ believed to be characteristic of the genus
Phyllochaetopterus (and thus thought to be present in
P. solitarius). The genus
Phyllochaetopterus is briefly discussed, notes on the biology and ecology of
S. solitarius are given, and features of tube structure are described and illustrated. Preliminary observations confirm that the species is able to reproduce asexually as well as sexually, as also suggested by Rioja.
