Association between Dentitheca habereri (Cnidaria: Hydrozoa) and two zoanthids

Dentitheca habereri is a leptomedusan hydroid forming large colonies on the fringing reefs of the Bunaken National Park (North Sulawesi, Indonesia). The hydroid is generally associated with two zoanthid species, Parazoanthus gracilis and Parazoanthus sp. Colonies lacking zoanthid epibionts are rare and generally smaller (8–10 cm). When associated withParazoanthus sp., the hydroid colonies are fan-shaped and may exceed 1m in width. In contrast, when D. habereri is colonised by the large polyps of Parazoanthus gracilis, the host colonies are smaller and the branching is irregular.