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Hydroids: Hydrozoa

Physical Characteristics, Behavior And Reproduction, Fire Coral (millepora Alcicornis): Species Accounts, No Common Name (distichopora Violacea): Species AccountsGEOGRAPHIC RANGE, HABITAT, DIET, HYDROIDS AND PEOPLE, CONSERVATION ST

FIRE CORAL (Millepora alcicornis): SPECIES ACCOUNTS
NO COMMON NAME (Distichopora violacea): SPECIES ACCOUNTS
NO COMMON NAME (Aglantha digitale): SPECIES ACCOUNTS
NO COMMON NAME (Aequorea victoria): SPECIES ACCOUNTS
PORTUGUESE MAN OF WAR (Physalia physalis): SPECIES ACCOUNTS

Hydroids live all over the world.

Hydroids live in all water habitats, from sea caves to deep-sea trenches, from lakes and ponds to rocky coasts and between grains of sand.


Hydroid polyps and medusae feed on almost all animals, from plankton, or microscopic plants and animals drifting in water, to fish.


The medusae of hydroids prey on the eggs and larvae of fish that people need for food. Some hydroids are used for scientific research. Others inhibit the functioning of power plants by clogging their pipes and reduce the speed of ships by attaching themselves to their hulls. Some medusae and polyp colonies inflict severe stings on humans.


Hydroids are not threatened or endangered.

Additional topics

Animal Life ResourceJellyfish, Sponges, and Other Simple Animals