Observations of the Life Cycle and Movement of the Thraustochytrid Ulkenia amoeboidea (Bahnweg & Sparrow) from the North Sea*

SYNOPSIS Two isolates of the thraustochytrid Ulkenia amoeboidea (Bahnweg & Sparrow) were obtained from the North Sea. In both isolates, the limax ameba liberated from the thallus rapidly assumed a nematode-like shape and movement characteristic of several sporozoan trophozoites. On rounding up, it underwent repeated binary fission and produced biflagellate zoospores.