Abstract
The ecological parameters of the association between the Urochordata Ciona intestin alisand the copepod Pachypygus gibberare investigated. This associated organism displays an aggregated distribution on the host population, and preferential site location within host individuals. The sex ratio observed is female biased. Even though this copepod lives at the expense of its host's feeding, the mean abundance and variance to the mean abundance ratio ß increase with host size, suggesting that the accumulation of this crustacean has no significant effect on either its host survival or growth. Although this associated copepod displays ecological features of parasites, it could be considered as a non costly partner.