<p><strong>Abstract</strong></p><p><strong> </strong><strong>Objective. </strong>Studies about sponge-zoanthid symbioses have been focused on understanding the specificity of the association, rather than testing what are the characteristics that make the host suitable to be colonized. For the first time it is investigated whether the Zoantharia <em>Parazoanthus </em>and <em>Epizoanthus</em> preference is related to the host sponge morphology (shape and mechanical resistance). <strong>Materials and methods.</strong> Sponges were categorized according to their shape and mechanical resistance. The presence/absence of zoanthids was recorded in 1,068 sponges at San Andres Island, and their habitat preference was evaluated using indices and confidence intervals. <strong>Results.</strong> 85 <em>Parazoanthus</em> colonies<em> </em>(78% of the total associations) and 24 <em>Epizoanthus </em>colonies (22%) were associated to sponges (10.2% in total). <em>Parazoanthus </em>uses branched and compressible sponges although prefers encrusting and fragile sponges, while <em>Epizoanthus </em>showes the opposite pattern, it can inhabit encrusting and fragile sponges but prefers branched and compressible sponges. <strong>Conclusion.</strong> These results indicated that sponge morphology is an important trait in zoanthid habitat selection. On the other hand, the similarity in the habitat used by zoanthids suggests the possibility of inter-generic competition if common resources are limited in time and space, while the differential habitat preference allows the competitive coexistence of both genera.</p> <p><strong>Key words: </strong><em>Epizoanthus</em>, host, <em>Parazoanthus</em>, symbiont, sponge, morphology<em>.</em></p><p> </p><br /><em></em>