Red Cushion Sea Star

The reproductive system in sea stars consists of a pair of gonads located in the inter-radial space of each arm. Both eggs and sperm are released into the surrounding water, which classifies their fertilization as external. Egg maturation is triggered by a neurosecretion produced by cells in the radial nerves. Sea stars are also well known for their remarkable regenerative abilities, capable of regenerating a complete starfish from a single arm under favorable conditions. The digestive system includes a mouth on the oral side, a short esophagus, and a stomach located in the central disc. Each arm houses pyloric ceca, where much of the digestion occurs. Digestion is primarily extracellular, but some intracellular digestion may take place within the ceca. A small intestine carries waste from the pyloric ceca to the anus, which is situated on the opposite side of the mouth in the central disc. Echinoderms, including sea stars, lack a true circulatory system. Instead, they possess a rudimentary hemal system, which is underdeveloped in sea stars, and its exact function remains poorly understood.