cnidarian

noun

cni·​dar·​i·​an nī-ˈder-ē-ən 

: any of a phylum (Cnidaria) of radially symmetrical, aquatic, invertebrate animals that have a hollow digestive cavity opening to the outside by a single opening surrounded by one or more nematocyst-studded whorls of tentacles, that occur as single or colonial sessile, typically columnar polyps or usually free-swimming, bell-shaped medusae, and that include the corals, sea anemones, jellyfishes, hydras, and Portuguese man-of-wars

Welcome to the world of cnidarians—a family of sea anemones, jellyfish and other marine invertebrates that kill their enemies and prey by firing poisonous, microscopic projectiles called nematocysts.

—Rick Weiss

called also coelenterate

cnidarian adjective

Examples of cnidarian in a Sentence

Recent Examples on the Web

The species documented included 33 molluscs, 23 annelids, 11 arthropods, five ribbon worms, four echinoderms, three cnidarians, and one bryozoan — spanning multiple branches of the animal kingdom. —Ryan Brennan, Miami Herald, 11 Mar. 2026

The species found included 33 molluscs, 23 annelids, 11 arthropods, five ribbon worms, four echinoderms, three cnidarians, and one bryozoan. —Ryan Brennan, Charlotte Observer, 11 Mar. 2026

Species documented in the Nankai Trough included 33 molluscs, 23 annelids, 11 arthropods, five ribbon worms, four echinoderms, three cnidarians, and one bryozoan — mollusks, worms, crustaceans, starfish relatives, and more, thriving in a place scientists barely knew anything about. —Ryan Brennan march 11, Kansas City Star, 11 Mar. 2026

The team observed the active and inactive periods of these cnidarians using infrared cameras and movement-tracking software. —New Atlas, 24 Jan. 2026

It’s not yet known quite how cnidarians and ctenophores create chromatin loops to add this extra layer of regulatory complexity to cell-type-specific gene regulation. —Quanta Magazine, 8 Oct. 2025

Moon jellies, like all of their cnidarian cousins, do use their stinging nematocyst cells to catch their prey, Brasher said. —Laylan Connelly, Oc Register, 20 Aug. 2025

The Sea Pen Sea pens are colonial cnidarians in the order Pennatulacea, named for their resemblance to antique quill pens when anchored in soft sediment. —Scott Travers, Forbes.com, 18 May 2025

So in the new study, Tissot and her colleagues turned to the freshwater cnidarian Hydra oligactis. —Bychristie Wilcox, science.org, 17 Sep. 2024

Word History

Etymology

New Latin Cnidaria, phylum name (from Greek knī́dē "nettle, sea nettle"—of uncertain origin— + Latin -āria, neuter plural of -ārius -ary entry 2) + -an entry 1

Note: The taxon Cnidaria is based ultimately on French cnidaire, a vernacular designation for a sub-class used by H. Milne Edwards in Histoire naturelle des coralliaires ou polypes proprements dits, tome 1 (Paris, 1857), p. 95. Milne Edwards alludes to use of Greek knī́dē for a sea nettle by Aristotle in Historia animalium, Book 5. The Greek noun has been associated with the verb knízein "to scratch, chop up, provoke" (perhaps from an Indo-European base *knid-), but the vowel length in knī́dē has no good explanation.

First Known Use

1894, in the meaning defined above

Rhymes for cnidarian

• agrarian
• aquarian
• barbarian
• bavarian
• bulgarian
• cimmerian
• hungarian
• librarian
• ovarian
• riparian
• rotarian
• sectarian

Kids Definition

cnidarian

noun

cni·​dar·​i·​an ni-ˈder-ē-ən 

: coelenterate

cnidarian adjective

Medical Definition

cnidarian

noun

cni·​dar·​i·​an -ē-ən 

: coelenterate

cnidarian adjective