ectosome

from The Century Dictionary.

• noun In sponges, the outer region, forming the roof and walls of the subdermal chambers, composed of ectoderm and a superficial layer of endoderm; the cortex: distinguished from choanosome and endosome.
• noun In cytology, one of the deeply staining granules eliminated from the chromatin of the nuclei of the germ-track during their karyokinetic divisions.