Identification by electron microscopy of marine nanoplankton from New Zealand, including the description of four new species

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Abstract
The marine nanoplankton of New Zealand has been examined for the first time by a combination of transmission and scanning electron microscopy. Of the c. 50 taxa found, practically all are known also from the Northern Hemisphere. As in this part of the world, the nanoplankton consists mainly of members of the systematic groups Chrysophyceae, Prymnesiophyceae (Haptophyceae), Loxo- and Prasinophyceae, and Choanoflagellida. Four new species are described: the prymnesiophytes Chrysochromulina novae-zelandiae and Phaeocystis scrobiculata, the choanoflagellate Bicosta antennigera, and Petasaria heterolepis, a flagellate of unknown affinities. Cells of the latter are covered by a scaly periplast, which contains both unmineralised and mineralised scales, of which the latter are siliceous (as demonstrated by X-ray microanalysis). In the New Zealand material 35 species could be identified, of which only the coccolithophorid Coccolithus huxleyi and the prasinophyte Pyramimonas grossii have been found in New Zealand previously. The remarkable similarity between the nanoplankton of the Northern and the Southern Hemispheres is discussed, based on these findings, and it is suggested that many of the flagellates are cosmopolitan, possibly occurring in cooler (deeper) water in the tropics. Some of the species recorded from New Zealand may be considered warm-water species (e.g., the choanoflagellate Parvicorbicula pulchella), others are known from cold water only (the unusual coccolithophorid genus Turrisphaera). Many of the flagellates occur, however, in a wide temperature interval.