Actinulida

Actinulida are an order of hydrozoans in the subclass Trachylinae. Very small, medusoid Hydrozoa without polyp phase, living in the sand interstitial, solitary, bell entirely or very much reduced, epidermis ciliated, 1-2 whorls of tentacles, statocysts present or not, club shaped and derived of ecto- and entodermal tissue; cnidome may include stenoteles.

Otohydra is a genus of cnidarians belonging to the monotypic family Otohydridae.

Halammohydridae is a family of cnidarians belonging to the order Actinulida.