noun, plural: ectoplasms
The outer, non-granulated, clear portion of the cytoplasm of a cell
The cytoplasm of certain species may be divided into endoplasm and ectoplasm. The inner dense part of the cytoplasm, and often granulated, is the endoplasm. The clear outer portion of the cytoplasm is the ectoplasm. While the endoplasm is adjacent to the nuclear envelope the ectoplasm lies immediately to the plasma membrane. Thus, the endoplasm houses the endomembrane system, which makes the endoplasm metabolically active. The ectoplasm, in turn, contains large numbers of actin filaments, and as such is associated with providing an elastic support for the cell membrane.1
In certain organisms such as amoeba, the ectoplasm is the thin, transparent, somewhat rigid, contractile portion of the cytoplasm. The differing consistencies of endoplasm and ectoplasm aid in the formation of pseudopods. Another function of ectoplasm in certain amoebae is for food ingestion. When the food comes in contact of an amoeba cell, the ectoplasm forms a tube called ectoplasmic tube, takes the food into it, and then converted into a food vacuole.2
In certain ciliates, the basal plates from where the cilia arise are embedded in the ectoplasm. In Paramecium, for instance, the ectoplasm contains the infraciliary system (as well as trichocysts).2
Word origin: Greek ekto(s)– (outside) + Greek -plasm(a) (that which has form)
1 Guyton, A. C. & Hall, J. E. Textbook of Medical Physiology, Eleventh Edition. Saunders.
2 Biosystematics, Structure and Functions of Invertebrates. Retrieved from http://assets.vmou.ac.in/MZO01.pdf.