any member of the order Gasterosteiformes, a group of fishes characterized generally by soft fin rays, pelvic fins located on the abdomen, an air bladder without a duct to the gut, and a primitive kidney. Gill structures are somewhat degenerate. Most species have bony rings around the body or ganoid (i.e., thick, bony, enamelled, and diamond-shaped) plates rather than scales. Families within the order are Gasterosteidae (sticklebacks), Aulorhynchidae (tube snout), Indostomidae (indostomid), Aulostomidae (trumpet fishes), Fistulariidae (cornetfishes), Centriscidae (shrimpfishes), Macrorhamphosidae (snipefishes), Solenostomidae (ghost pipefishes), and Syngnathidae (pipefishes and sea horses)
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