Amoebocytes

Amoebocytes are amoeboid cells found in certain invertebrates, most notably in sponges (Porifera). They reside in the mesohyl, the gelatinous middle layer of the sponge, and move through the tissue by extending pseudopodia. In sponges they are often referred to as archaeocytes and are capable of phagocytosis, taking up food particles and transporting nutrients to other cells.

Amoebocytes are versatile and, in many species, totipotent. They can differentiate into several other sponge cell types, including porocytes (lining the water canals), choanocytes (collar cells that drive water flow and filter feeding), sclerocytes (secreting spicules), and spongocytes or collencytes (involved in skeletal and connective tissue elements). Through this differentiation, amoebocytes contribute to digestion, distribution of absorbed nutrients, and the maintenance of the sponge’s internal architecture.

In addition to nutrient transport and tissue maintenance, amoebocytes participate in skeletal formation and regeneration. They can secrete skeletal components such as spicules (siliceous or calcareous) or spongin fibers and help repair damaged tissue. They may also give rise to gametes in some species, contributing to reproduction.

Amoebocytes thus play a central, multifunctional role in sponge biology, supporting digestion, nutrient distribution, skeletal construction, wound healing, and sometimes reproduction. In broader invertebrate biology, the term amoebocyte is used for other mobile, phagocytic cells, but in sponges these cells are especially integral to organismal physiology and regeneration.