Studies on marine choanoflagellates III. An electron microscopical survey of the genus Acanthoecopsis

The external morphology of 3 choanoflagellates A. spiculifera, A. apoda and A. unguiculata, was investigated by EM of whole mounts. The material came from various localities in the transition area between the brackish Baltic Sea and the Atlantic-influenced North Sea. A. spiculifera (the type species of its genus) differed from A. apoda by a number of lorica characters in addition to the presence or absence of a pedicel. The most prominent distinguishing feature was the placement of the anterior transverse costae. A. unguiculata which cannot be confounded with either of the above mentioned species, was observed during cell division. A description of the division process is given. A. spiculifera is a new record from North Atlantic waters, whereas A. apoda and A. unguiculata have been frequently encountered in the North Atlantic plankton. Typification of the genera included under the family Acanthoecaceae, EM investigation of the nomenclatural types and the delimitation of the genus Acanthoecopsis against the remaining genera comprising species with a costal component to the lorica are discussed.