Amoebocyten

Amoebocyten, or amoebocytes, are a type of mobile, irregularly shaped cells defined by their amoeboid movement, which uses pseudopodia to extend and retract parts of the cytoplasm. They occur in several invertebrate groups, most notably in sponges, and are described in relation to either connective-tissue-like roles or immune functions depending on the species.

In sponges (phylum Porifera), amoebocytes reside in the mesohyl, the gelatinous middle layer between the outer pinacoderm and the choanocyte chambers. They participate in feeding and digestion by phagocytosing suspended particles and distributing digested nutrients to other cells. They are versatile and can differentiate into other cell types as needed, including archeocytes, gametes, and skeletal-forming cells that contribute to the production of spicules or spongin.

Outside sponges, amoeboid cells are common components of invertebrate innate immunity. Circulating amoebocytes, or coelomocytes in some groups, patrol the body cavity, migrate to sites of infection or damage, phagocytose bacteria and debris, and secrete enzymes or antimicrobial peptides. They also participate in wound healing and can contribute to clot-like responses in certain species.

Amoebocyten represent a primitive and adaptable cell type that illustrates how cells can assume multiple roles—from nutrient distribution and growth to defense and regeneration—in early-diverging animal lineages.