An amebocyte or amoebocyte (/əˈmiː.bə.saɪt/) is a mobile cell (moving like an amoeba) in the body of invertebrates including echinoderms, molluscs, tunicates, sponges and some chelicerates. They move by pseudopodia. Similarly to some of the white blood cells of vertebrates, in many species amebocytes are found in the blood or body fluid and play a role in the defense of the organism against pathogens. Depending on the species, an amebocyte may also digest and distribute food, dispose of wastes, form skeletal fibers, fight infections, and change into other cell types.

Limulus amebocyte lysate, an aqueous extract of amebocytes from the Atlantic horseshoe crab (Limulus polyphemus), is commonly used in a test to detect bacterial endotoxins.[1]

In sponges, amebocytes, also known as archaeocytes, are cells found in the mesohyl that can transform into any of the animal's more specialized cell types.[2][3]

In older literature, the term amebocyte is sometimes used as a synonym of phagocyte.

In tunicates they are blood cells and use pseudopodia to attack pathogens that enter the blood, transport nutrients, get rid of waste products, and grow/repair the tunica.[4]


  1. Levin J, Bang F.B. (1968). "Clottable Protein in Limulus: Its Localization and Kinetics of Its Coagulation by Endotoxin". Thromb. Diath. Haemorrh. 19 (1): 186–97. PMID 5690028.
  2. "An Online Introduction to the Biology of Animals and Plants - Sponges and Cnidaria".
  3. "The Porifera - Invertebrate Biology Course".
  4. Cima, Francesca; Ballarin, Loriano; Gasparini, Fabio; Burighel, Paolo (2006-01-01). "External amebocytes guard the pharynx entry in a tunicate (Ascidiacea)". Developmental & Comparative Immunology. 30 (5): 463–472. doi:10.1016/j.dci.2005.07.004. PMID 16182366.

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