Starfish: a general term for marine invertebrates, not fish. Flat and star. Wrist. There are 1 1,800 species in existence, distributed in various oceans, with the most species in the North Pacific. Radial diameter 1? 65 cm, mostly 20? 30 cm (8? 12 inch). The wrist is hollow and covered with short thorns and forked thorns; There are rows of pipe legs (some with suction cups at the ends) in the ditch below, so that starfish can crawl in any direction and even climb up the steep surface. Lower starfish feed on food particles along the entrance of wrist groove. Higher kinds of stomachs can be turned upside down as bait for in vitro digestion or swallowed whole. The endoskeleton consists of calcareous bone plates. Breathe through the skin. There is a bright spot on the wrist. Most of them are hermaphroditic, and a few are hermaphroditic; Some have asexual division and reproduction.