EVERYDAY SCIENCE

Detailed explanation-1: -Hydrozoa. The class hydrozoa is the most diverse class of cnidarians and includes siphonophores, hydroids, fire corals, and many free-swimming medusae species.

Detailed explanation-2: -The Hydrozoa are mostly marine predators that constitute a class in the Cnidaria, to which the corals and jellyfish also belong. Hydroids are a polyp life stage of most hydrozoans, which may be colonial.

Detailed explanation-3: -Unlike some other cnidarian groups, the lining of the central cavity lacks stinging nematocysts, which are found only on the tentacles and outer surface. All colonial hydrozoans also include some polyps specialized for reproduction.

Detailed explanation-4: -They are distinguished from other groups by their complex life cycle, by the growth of medusae from buds rather than strobilae or from metamorphosis, by the presence of a velum inside the bell of the medusa, and by the production of gametes from ectodermal, rather than endodermal, tissue.

Detailed explanation-5: -Cnidarians are incredibly diverse in form, as evidenced by colonial siphonophores, massive medusae and corals, feathery hydroids, and box jellies with complex eyes. Yet, these diverse animals are all armed with stinging cells called nematocysts.