jellyfish
Pluraljellyfish, jellyfishes
- 1A nearly transparent aquatic animal with a jellylike appearance, especially one of the larger species once classed among the acalephs.
Like a living, drifting parasol made of clear jelly.
A glowing jellyfish pulsed slowly through the deep water beyond the reef.
The current carried a translucent jellyfish toward the crowded beach.
Similarjelly
Note
The everyday sense, and the one the name describes. The jelly comes through Old French gelee from Latin gelō, so the animal is named for its jellylike look. The plural is usually jellyfish, though jellyfishes also occurs, and the word sits easily before other nouns, as in jellyfish venom. Acalephs belongs to an older classification that grouped stinging medusae with the comb jellies.
- 2Any of various stinging cnidarians of the subphylum Medusozoa, including box jellyfish, true jellyfish, stalked jellyfish, and certain hydrozoans.
Marine biologists classify the jellyfish among the cnidarians, not among true fish.
A jellyfish has no brain, yet it hunts and stings prey with remarkable efficiency.
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Note
Here the word is a zoologist's umbrella over the stinging medusozoans, and it is wider than the group names inside it suggest. Only the class Scyphozoa are true jellyfish. Box jellyfish and stalked jellyfish are jellyfish in this broad sense but not true ones, and certain hydrozoans qualify as well. The comb jellies fall outside it, though everyday speech often includes them under the ctenophore meaning.
- 3A comb jelly, a transparent marine animal of the phylum Ctenophora that swims using rows of beating cilia.
The rainbow shimmer along that jellyfish comes from light scattering off its beating rows of cilia.
A drifting jellyfish trapped tiny plankton on sticky cells rather than stunning them with venom.
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Note
A loose popular use that zoology does not share. Comb jellies look like jellyfish and drift in the same water, but they form a separate phylum and move by rows of cilia instead of stinging their prey. Specialists keep jellyfish for the cnidarians and call these animals ctenophores or comb jellies. In careful writing, those names are the safer choice.
- 4The medusa phase of a medusozoan cnidarian (the mature, free-swimming bell) rather than an earlier life stage such as the polyp.
Like the adult butterfly that follows the caterpillar: the same creature in its grown, free-moving form.
Only after the polyp releases it does the young jellyfish pulse away into open water.
Researchers tracked how quickly each released jellyfish reached its full adult size.
Similarjelly
Note
A life-cycle word: biologists use it for the free-swimming bell alone. The same animal begins as a larva and then becomes a polyp fixed to a surface, and neither stage is a jellyfish in this sense. It becomes one only when the medusa is released. In writing about development, polyp and medusa are the precise pair, and jellyfish serves as the plain name for the second.
- 5A sudoku solving technique in which the possible cells for a digit fall within exactly four rows and four columns, allowing that digit to be eliminated as a candidate elsewhere in the grid.
He paused mid-grid, traced a jellyfish through four rows, and erased a cluster of penciled candidates.
A clean jellyfish on the fives finally unlocked the rest of the puzzle.
Note
Puzzle solvers' jargon, used as a count noun: you spot a jellyfish, or a jellyfish on the fives. The logic is a squeeze. Suppose every possible cell for a digit in four rows lies within the same four columns. Those four rows must then place the digit in those columns, so the digit can be erased from every other cell in them.
Practice
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Origin
A compound of jelly + fish, naming an aquatic (fish-like) creature that is gelatinous, or jelly-like. Despite the name, jellyfish are not biologically classified as fish.