The Hydrozoa Directory - Information about the classification, anatomy, and life cycle of this class, including photographs and diagrams. Also provides biographies and photos of hydrozoan systematists and marine naturalists of the past. Image gallery: Hydra - Includes downloadable video clips of the behavior of a typical hydra extending and contracting. Hydra Oligactis - Rosemarie Arbur has made a series of drawings of a hydra devouring a water flea. Hydras - Photographic study by Jan Parmentier of these organisms, with images of various reproductive structures. Hydra - Overview of this freshwater polyp with photographs of a budding specimen and several closeup views. Portuguese Man of War - Research project by Rissa Niemi on this jellyfish including its classification, habitat, reproduction, adaptations, nutrition and interactions with other species. Vallentinia gabriellae - Taxonomy, description and photograph of the hitch-hiking jellyfish, its habitat and distribution, life history and community ecology. Green Hydra: Chlorohydra viridissima - Photographs and information on this organism. Brown Hydra: Hydra oligactis - Photographs and information from ARKive including description, range, habitat, biology, threats and conservation. Fire Corals: Millepora spp. - Photographs and information from ARKive including classification, status, description, range, habitat, biology, threats and conservation. Lace Coral: Stylaster californicus - Photographs and information from ARKive including classification, status, description, range, habitat, biology, threats and conservation.