A multifunctional cell type that is a key component of the immune defences of most invertebrate animals. Haemocytes are found in the coelom and blood vessels of coelomate animals and perform a variety of functions. For example, in insect larvae they can engulf foreign particles by phagocytosis, secrete opsonins (see opsonization) and other antimicrobial compounds to promote destruction of invading organisms, encapsulate larger pathogens, such as the eggs of parasitic wasps, and attack them by secreting reactive oxygen species. Haemocytes also promote blood coagulation and repair of damaged tissues and serve various metabolic functions.