Definition of hydroid in English:



  • A coelenterate of an order that includes the hydras. They are distinguished by the dominance of the polyp phase.

    • ‘The most numerous inhabitants are hydroids and copepods.’
    • ‘On the walls are a riot of soft corals, sponges, hydroids and anemones in all shapes and sizes.’
    • ‘There were dense walls of soft corals, sponges, anemones and hydroids, nudibranchs, creepy-crawlies and lots of fish.’
    • ‘Aside from its temporary and permanently resident fish, the underside is decorated with sponges, hydroids, tunicates, tube worms, cup corals and anemones.’
    • ‘Colonies may be mistaken for hydroids, corals, or even seaweeds.’


  • 1Relating to coelenterates of the hydroid group.

    • ‘Before long, similar green proteins were detected in many bioluminescent coelenterates including various medusae, apparently all luminescent hydroid polyps, and a few others.’
    • ‘Along the tops of the walls and gullies are many small hydroid clumps which, in turn, attract a range of delicately coloured nudibranchs that feed on them.’
    • ‘He had shown that hydroid jellyfish known as naked-eyed medusae reproduce not only by spewing eggs, but also by asexual budding, which he found marvelous to behold.’
    • ‘The hydroid tissues, in particular, are the general run of moss water storage cells and are probably only remotely related to the xylem of tracheophytes.’
    1. 1.1
      another term for polypoid


Mid 19th century: from hydra + -oid.