Jan Hamrsky / Brown hydra (Hydra oligactis) polyps attached to the stone, Europe, September, controlled conditions

Jan Hamrsky / Brown hydra (Hydra oligactis) digesting the prey enclosed within the body cavity, Europe, September, controlled conditions

Jan Hamrsky / Brown hydra (Hydra oligactis) with two buds on the body wall, extending its tentacles, Europe, September, controlled conditions

Willem Kolvoort / Underwater Brown hydra (Hydra oligactis) on water plant, Lake Naarden, Holland

Willem Kolvoort / Underwater Brown hydra (Hydra oligactis) in sand winning pit, Holland

Willem Kolvoort / Brown Hydra (Pelmatohydra / Hydra oligactis) Holland