Starfish eat crustaceans, shellfish, fish, polychaetes and various invertebrates, and some starfish can also eat bivalves. Starfish are marine echinoderms with a "mouth" underneath their body. Its digestive system includes two stomachs, one of which can be ejected from the body and used to eat directly. They first "wrap" the prey and bind it to the "mouth" in the center of the abdominal disk.

Introduction to starfish

Starfish are the most representative group of echinoderms in terms of structure and physiology. The body is flat, mostly with five-radiation symmetry, and the boundary between the body disk and the wrist is not obvious. When living, speak with your mouth facing downwards and your retorts with your mouth facing upwards. There is a walking belt groove on the ventral side of the wrist, and the tube feet protrude from the groove. The bony plates of the endoskeleton are connected by connective tissue and are flexible and flexible.

The surface of the starfish body has spines and spines, which are protrusions of the bones. The membranous vesicular protrusions protruding from between the bone plates are covered with epithelium and lined with body cavity epithelium. Its inner cavity is connected to the secondary body cavity and is called dermal gills. It has the functions of breathing and diffusing metabolites to the outside world. The water pipe system is well developed. During ontogeny, there are transfeather-brachial larvae and brachybrachial larvae.

The radial diameter of starfish is 1-65 cm, most of which are 20-30 cm. The wrist is hollow and covered with short spines and forked spines. There are rows of tube feet (some with suckers at the end) in the trench below, allowing the starfish to crawl in any direction, even up steep surfaces. Lower starfish feed on food particles that enter the mouth along the carpal groove. The stomach of advanced species can be turned over to the food for external digestion, or it can be swallowed whole.