The ultrastructure of the eyes of Paravortex karlingi (Plathelminthes, Rhabdocoela)

Abstract

Both eyes of Paravortex karlingi belong to the rhabdomeric type. Each eye consists of a single pigment cup cell and three sensory cells. Modified mitochondria lie in three protrusions of the cup cell, and several of these mitochondria form giant mitochondrial derivates. The centres of the derivates include electron-dense substances. These modified structures may have lenticular functions. Furthermore, it is shown that giant mitochondrial derivates develop by fusion of smaller ones. Embryos have many small mitochondria in the developing eyes whereas the adult possesses less numerous, but giant forms. This circumstance leads to the assumption that all such lenticular structures within the rhabdocoels result from identical processes.