Cell morphology and life history of D ictyocha octonaria ( D ictyochophyceae, O chrophyta) from W ellington H arbour, N ew Z ealand

Summary Even though many aspects of D ictyocha fibula and D . speculum have long been studied, very little is known about D . octonaria . For the first time a clonal culture derived from a single cell of D . octonaria from Wellington Harbour was studied in detail. In the skeleton‐bearing stage three morphotypes were observed – skeleton bearing, mucocyst‐bearing and amoeboid, while in the naked stage only the naked form was studied. In this study the mucocyst‐bearing form was described as a new morphotype. Vegetative reproduction of the skeleton‐bearing form in the exponential growth phase was by both direct binary fission and by first forming a doublet and then two separate daughter cells, while that of naked form was by simple binary fission. Occasionally double skeletons were observed as end products of both the vegetative and sexual reproductions. In sexual reproduction all three forms in the skeleton‐bearing stage exhibited the same polymorphic life history involving a multinucleate stage. The newly formed daughter cells of all three forms developed individual siliceous skeletons prior to being released from the parent cell. The naked form in the naked stage, however, exhibited a separate polymorphic life history that produced only skeleton‐free daughter cells. For the first time both vegetative and sexual reproduction of D . octonaria were documented.