A study about species composition, relative abundance, densities, size composition, reproductive and recruiting periods, sex proportion and species diversity of the decapod populations associated to worm reefs of P. caudata (Kröyer, 1856) was carried out. Monthly, samples of worm reef were obtained from August/1997 to July/1998 from Caiobá Beach, Matinhos (25º51 'S and 48º32'W), Paraná State, southern Brazil. Air temperature oscillated from 14.5ºC (July) to 31.0ºC (February), surface water from 18.0ºC (July) to 28.0ºC (January and February), and the salinity from 22%0 (February) to 34%0 (September). Eigth decapod species were found: Petrolisthes armatus (Gibbes, 1850); Pachygrapsus transversus (Gibbes, 1850); Panopeus americanus Saussure, 1857; Eurypanopeus abbreviatus (Stimpson, 1860); Menippe nodifrons Stimpson, 1859; Pilumnus dasypodus Kingsley, 1879; Eriphia gonagra (Fabricius, 1781); and Alpheus heterochaelis Say, 1818. The total density varied from 1.66 ind./l (September) to 33.93 ind./l (January). Petrolisthes armatus was the most numerous species. Six species were constant, one was accessory, and another accidental. Shannon-Wiener diversity index was the lowest when compared with other similar habitats. Ovigerous females occurred in six species, but no species showed continuous breeding all year round. The majority of the associated decapods were smaller than those reported in the literature.
Decapod crustacean; association; Phragmatopoma; Caiobá