Science, Tech, Math › Science Biology Prefixes and Suffixes: Ect- or Ecto- Share Flipboard Email Print Spitting Cobra: Snakes and other reptiles are ectotherms and must obtain heat from their external environment. Digital Vision / Getty Images Science Biology Basics Cell Biology Genetics Organisms Anatomy Physiology Botany Ecology Chemistry Physics Geology Astronomy Weather & Climate By Regina Bailey Biology Expert B.A., Biology, Emory University A.S., Nursing, Chattahoochee Technical College Regina Bailey is a board-certified registered nurse, science writer and educator. Her work has been featured in "Kaplan AP Biology" and "The Internet for Cellular and Molecular Biologists." our editorial process Regina Bailey Updated September 07, 2019 The prefix ecto- comes from the Greek ektos, which means outside. (Ecto-) means outer, external, out, or outside. Related prefixes include (ex- or exo-). Words Beginning With (Ecto-) Ectoantigen (ecto - antigen): An antigen that is located on the surface or exterior of a microbe is known as an ectoantigen. An antigen is any substance that elicits an antibody immune response. Ectoblast (ecto - blast): a synonym for an epiblast or an ectoderm. Ectocardia (ecto - cardia): This congenital condition is characterized by displacement of the heart, particularly a heart that is outside of the chest cavity. Ectocellular (ecto - cellular): of or pertaining to an object external to a cell or outside of the cell membrane. Ectocornea (ecto - cornea): The ectocornea is the outer layer of the cornea. The cornea is the clear, protective layer of the eye. Ectocranial (ecto - cranial): This term describes a position that is external to the skull. Ectocytic (ecto - cytic): This term means outside of or external to a cell. Ectoderm (ecto - derm): Ectoderm is the outer germ layer of a developing embryo that forms skin and nervous tissue. Ectodomain (ecto - domain): a biochemical term that denotes the part of a polypeptide on the cell membrane that reaches into the extracellular space. Ectoenzyme (ecto - enzyme): An ectoenzyme is an enzyme that is attached to the outer cell membrane and is secreted externally. Ectogenesis (ecto - genesis): The development of an embryo outside of the body, in an artificial environment, is the process of ectogenesis. Ectohormone (ecto - hormone): An ectohormone is a hormone, such as a pheromone, that is excreted from the body into the external environment. These hormones typically alter the behavior of other individuals of the same or different species. Ectomere (ecto - mere): This term refers to any blastomere (a cell resulting from cell division that occurs after fertilization) that forms the embryonic ectoderm. Ectomorph (ecto - morph): An individual with a tall, lean, thin body type predominated by tissue derived from the ectoderm is called an ectomorph. Ectoparasite (ecto - parasite): An ectoparasite is a parasite that lives on the outer surface of its host. Examples include fleas, lice, and mites. Ectophyte (ecto - phyte): An ectophyte is a parasitic plant that lives on the outer surface of its host. Ectopia (ecto - pia): The abnormal displacement of an organ or body part outside of its proper location is known as ectopia. An example is ectopia cordis, a congenital condition where the heart sits outside of the chest cavity. Ectopic (ecto - pic): Anything that occurs out of place or in an abnormal position is called ectopic. In an ectopic pregnancy, a fertilized egg attaches to a fallopian tube wall or other surface that is outside of the uterus. Similarly, an ectopic beat refers to electrical disturbances in the heart outside of the normal initiation in the SA node. Ectoplasm (ecto - plasm): The outer area of the cytoplasm in some cells, such as protozoans, is known as ectoplasm. Ectoproct (ecto - proct): synonym for a bryozoan. Ectoprocta (ecto - procta): animals commonly known as oryonzoans. Ectoprocta is a phylum of non-motile aquatic animals. While the individuals are very small, the colonies that they live in can grow comparatively quite large. Ectoprotein (ecto - protein): Also called an exoprotein, an ectoprotein is the term for an extracellular protein. Ectorhinal (ecto - rhinal): This term refers to the exterior of the nose. Ectosarc (ecto - sarc): The ectoplasm of a protozoan, such as an amoeba, is called the ectosarc. Ectosome (ecto - some): An ectosome, also called an exosome, is an extracelluar vesicle that is often involved in cell-to-cell communication. These vesicles that contain proteins, RNA, and other signaling molecules bud off from the cell membrane. Ectotherm (ecto - therm): An ectotherm is an organism (like a reptile) that uses external heat to regulate its body temperature. Ectotrophic (ecto - trophic): This term describes organisms that grow and obtain nutrients from the surface of tree roots, such as mycorrhiza fungi. Ectozoa (ecto - zoa): refers to animal parasites who live externally on other animals. Examples include the louse or the flea, both parasitic insects. Ectozoon (ecto - zoon): An ectozoon is an ectoparasite living on the surface of its host.