A redescription of Rhabdamoeba marina, an inconspicuous marine amoeba frombenthic sediments

Rhabdamoeba marina was isolated from coastal waters off the Isle of Cumbrae , Scotland. It is worthy of attention for two reasons. Firstly, it is an ex ample of a marine amoeba that is easily overlooked in fresh or enriched sam ples despite its widespread distribution within these waters. Secondly, the validity of the genus Rhabdamoeba has been questioned mainly because the o riginal description by Dunkerly (1921) was brief and based solely on preser ved material. The present redescription of this isolate, based on light and electron microscopy, removes the confusion surrounding the status of the g enus. Amoebae are between 5.0 and 25.0 mu m in length, and are essentially stationary apart from the occasional extension of a long, active, feeding p seudopodium up to 50 mu m from the cell body. The pseudopodia of stationary cells are distinctive, appearing as knob-like or foot-like extensions arou nd the cell body. Small papillae at the tips of these pseudopodia are evide nt at high magnifications by Light and scanning electron microscopy. Diagno stic features of note at the ultrastructural level include a cell surface w ithout a glycocalyx and a nucleus with a central nucleolus (i.e., vesicular nucleus) which is common in small amoebae. The cytoplasm contains Golgi ci sternae and the mitochondria have tubular cristae. The life cycle of this p rotist includes a flagellated stage that has not previously been reported.