Hydrozoa

Hydrozoa is a class of small, aquatic animals within the phylum Cnidaria, which also includes jellyfish and corals. They often exist as colonies made up of many tiny, specialized individuals working together, though some are free-living. Hydrozoans can have different forms, including polyp (sessile, tube-shaped) and medusa (free-swimming, bell-shaped). They capture food using their stinging cells, called cnidocytes. Common examples include freshwater hydras and the colonial Portuguese man o’ war, which appears like a single organism but is a collection of specialized creatures. Hydrozoans play important roles in aquatic ecosystems as predators and prey.