Hydractinia van Beneden, 1841

Hydroid colony either stolonal with a reticular hydrorhiza of perisarc-covered stolonal tubes or covered by encrusting mat; hydrorhizal mat may secrete chitinous or calcareous skeleton or spines, pillars or branches. Polyps sessile, polymorphic, naked, gastrozooids with one or more whorls of oral filiform tentacles or with scattered tentacles on the distal half of body, dactylozooids when present with or without tentacles. Reproduction by sessile sporosacs or free medusa, gonophores typically borne on gonozooids; gonozooids with one or more whorls of oral tentacles or without tentacles and mouth, giving rise to fixed sporosacs, eumedusoids or free medusa.