Non-contractile pouch that is connected to the anterior stomach through a slit-like opening. This pouch is also well-connected to the haemal system through numerous haemal ducts within its connective tissue layer. [ http://www.ncbi.nlm.nih.gov/pubmed/20955602 ]
Term information
The digestive tract of many metazoan invertebrates is characterized by the presence of caeca or diverticula that serve secretory and/or absorptive functions. With the development of various feeding habits, distinctive digestive organs may be present in certain taxa. This also holds true for sea urchins (Echinodermata: Echinoidea), in which a highly specialized gastric caecum can be found in members of a derived subgroup, the Irregularia (cake urchins, sea biscuits, sand dollars, heart urchins, and related forms)... Homologous with the more or less pronounced dilation of the anterior stomach that is observed in most "regular" sea urchin taxa[PMID:20955602]