An ultrastructural survey of the chrysophycean genusParaphysomonasunder natural conditions

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Abstract
Electron microscopical examination of whole mounts, prepared from freshly collected seawater samples from the Isefjord area (Denmark), has led to the enumeration of seven species belonging to the chrysophycean genus Paraphysomonas. One of these is P. sideriophora sp. nov., characterised by its single type of scale, each resembling a flat-iron. Three of the species have previously been recorded from Denmark. Most of the type descriptions of Paraphysomonas species refer to accidentally cultured material. When the same species are observed under natural conditions, as in the present investigation, the variation in scale size and morphology is seen to be considerably wider than reported in the type descriptions. This applies in particular to P. foraminifera Lucas and P. imperforata Lucas. The discrepancies between the type descriptions and the present material is probably a reflection of the fact that cultured material consists of one or a few clones only (sexual reproduction is unknown), whereas the immediate processing for electron microscopy of freshly collected seawater samples, carried out over a longer period, probably provides material from several clones. The taxonomy of the various scale-covered heterokont genera of the Ochromonadales is briefly discussed.