FIRST EVIDENCE OF MITOCHONDRIAL LENSING IN 2 SPECIES OF THE TYPHLOPLANOIDA (PLATHELMINTHES, RHABDOCOELA) - PHYLOGENETIC IMPLICATIONS

Based on electron-microscopical observations the light-sensing organs of Proxenetes deltoides and Ptychopera westbladi, representatives of t he ''Typhloplanoida'' Trigonostominae, are described. The photorecepto rs in both species belong to the type of rhabdomeric pigment cup ocell i. P. deltoides has a single pigment cell and three sensory cells. P. westbladi possesses eyes made up of a single pigmented cup cell and a single sensory cell. The dioptric apparatus in the eyes of P. deltoide s is formed by three proliferations of the cup cell containing giant m itochondria. In P. westbladi, the elements focalizing incoming light a lso consist of modified mitochondria which are arranged in the section of the cup cell covering the eye cavity. With regard to the new findi ngs, mitochondrial lensing is hypothesized as an autapomorphy of a mon ophylum encompassing distinct taxa or all members of the free-living R habdocoela; the Neodermata also belong to this monophylum.