The extracellular calcification of zoospores ofPhacotus lenticularis(Chlorophyta, Chlamydomonadales)

Abstract

In nature the zoospores of Phacotus lenticularis usually have a conspicuous, bivalved lorica. It consists of two clearly distinguishable layers: an outer calcite layer formed of rings of staggered calcite crystals with electron-opaque rod-like components between the crystals, and an underlying electron-opaque layer. Underneath the lorica a mucilaginous sheath is present. The ultrastructural development of these extracellular layers was studied by scanning electron microscopy and transmission electron microscopy of flat-embedded specimens from the natural habitat, Lake Feldberger Haussee (Baltic Lake District, Germany). During vegetative propagation, the two mother shells separate but remain attached to the mucilaginous zoosporangium which is formed between the shells. Usually two longitudinal cell divisions result in four naked zoospores in the sporangium. These begin to form new extracellular material, consisting initially of an electron-opaque layer that becomes detached by the formation of a mucilagino...