Kinorhynchs are free-living marine animals generally 1 mm or smaller, somewhat larger than rotifers and gastrotrichs. A kinorhynch moves ahead by forcing body fluid into its head and thereby everting, anchoring with scalids - spines - on its head in sand grains or mud and then hauling itself forward as it retracts its head. Kinorhynchs do not swim. The name kinorhynch, meaning moveable snout, refers to the kinorhynch head. Microscopic neck plates cover the head when the kinorhynch inverts its protrusible snout. Some kinorhynch species retract both head and neck.