hydrozoans
Refers to the class Hydrozoa, a group of small predatory animals including hydras and Portuguese man o' war. Used in biological and taxonomic contexts.
Hydrozoans belong to the phylum Cnidaria.
A variety of hydrozoans are observed in this sea area.
From ヒドロ (hydro-) + 虫類 (insect/creature class), a calque of the scientific name Hydrozoa.