mitosome

Century Dictionary and Cyclopedia

1. n. In cytology, a body formed from the spindle-fibers of the secondary spermatocytes, said to give rise to the middle-piece and tail envelop of the spermatozoön: probably equivalent to the ‘Nebenkern’ of La Valette St. George.

Wiktionary

1. n. cytology An organelle found within certain unicellular eukaryotes which lack mitochondria.