Coelomocytes

Coelomocytes are free-floating cells that inhabit the coelomic fluid of coelomate animals, most notably echinoderms such as sea stars and sea urchins, but also found in other invertebrates. They circulate within the body cavity and can be collected by puncturing the coelomic sac or by gentle extraction.

Morphology and diversity: Coelomocytes are heterogeneous, including amoeboid phagocytes, granular cells, vibratile cells, and other forms such as spherulocytes or crystal cells depending on species. They are typically nucleated and may contain enzyme-rich granules or pigment inclusions.

Functions: The primary roles are immune defense and tissue maintenance. Coelomocytes participate in phagocytosis of bacteria and debris, encapsulation of foreign bodies, and wound repair. They also produce soluble antimicrobial factors, participate in coagulation of coelomic fluid after injury, and contribute to cellular or humoral defense responses in invertebrate innate immunity.

Origin and biology: Coelomocytes originate from mesodermal tissues and are produced within the walls of the coelom. They can have varying lifespans, and their numbers and activity can reflect the health status of the animal; environmental stressors can alter coelomocyte counts and function.

Research context: Invertebrate immunology studies use coelomocytes to understand primitive immune mechanisms, host-pathogen interactions, and the evolution of immune systems. They are also used as model cells in studies of phagocytosis, cytotoxic responses, and coagulation in marine organisms.