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.

—R. Weiss

called also coelenterate

cnidarian adjective

Examples of cnidarian in a Sentence

Recent Examples on the Web

An arm and a leg Jellyfish are cnidarians, a phylum of soft-bodied invertebrates. —Elizabeth Rayne, Ars Technica, 3 Jan. 2024

Jellyfish and their relatives, collectively known as cnidarians, are considered to be the earliest living animals to develop nervous systems. —Melissa Rudy, Fox News, 24 Sep. 2023

What’s more, similar genes and molecules seem to control sleep in cnidarians, as compared with other animals and humans. —Stephanie Pappas, Scientific American, 16 June 2023

Is our cnidarian learning? —John Timmer, Ars Technica, 22 Mar. 2023

If these typical cnidarians strike you as a bit bizarre, the myxozoans are even further out past the borders of the familiar. —John Timmer, Ars Technica, 26 Feb. 2020

In 1995, however, Mark Siddall, then at the Virginia Institute of Marine Science, and his colleagues argued that myxosporeans are weird members of the cnidarians, the group that includes jellyfish and corals. —Quanta Magazine, 19 Aug. 2019

The fork leading to cnidarians represents the final turnoff before animals become bilaterally symmetric, which makes them an interesting group to study because of the greater complexity that came with that later innovation. —Quanta Magazine, 8 Jan. 2019

To find out, the researchers decided to sequence the genome of Aurelia, the moon jellyfish, and then compare it to those of cnidarians without medusas. —Quanta Magazine, 8 Jan. 2019

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

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