The utilization of polychaetes in descriptive ecology is reviewed in the light of recent research especially concerning the biota hard bottom environments. Polychaetes, often linked in the past to the concept of opportunistic species able to proliferate

The Syllidae are geographically widespread polychaetes, particularly diverse and abundant on marine hard bottoms and in seagrass meadows. Hydrodynamics, habitat complexity and biological traits are hypothesized to influence syllid bathymetric distribution.

Based on material collected during the DIVA-Artabria I project (2002 cruise) from deep areas (629-1132m) of the shelf and upper slope off the Ártabro gulf (Galicia, NW Spain), two new species of Syllidae (Annelida: Polychaeta) are described. Eurysyllis