Six new Actinella (Bacillariophyta) species from Papua New Guinea, Australia and New Zealand: further evidence for widespread diatom endemism, in theAustralasian region

Examination of sediment samples from oligo-and dystrophic ponds, lakes and streams in Papua New Guinea. Australia and New Zealand revealed a hitherto unknown diversity of the diatom genus Actinella Lewis. Six new species are proposed, viz. Actinella aotearoaia sp. nov., A. giluwensis sp. nov., A ind istincta sp. nov., A. muylaertii sp, nov., A. parva sp. nov. and A. pulchel la sp. nov. All species are heteropolar, both in girdle and valve view. Nov el information on the genus Actinella includes the observations of two ribb on-shaped. valve-appressed plastids in A. aotearoaia and A. pulchella, and the presence of long mucilage stalks in A. aotearoaia. It is argued that, d espite recent proposals to reduce the genera Actinella and Desmogonium Ehre nberg to the rank of subgenera of Eunotia, they should be kept separate unt il the taxonomic significance of their distinctive morphological features ( such as heteropolarity) is fully assessed. The new species appear to be end emic to Australasia and have distinct biogeographies within this region. Ex cept for A, aotearoaia, all species are present in Tasmania. A. indistincta and A. pulchella have also been found in New Zealand (Stewart Island). A. aotearoaia is common in several localities in New Zealand but was also foun d near Sydney on the Australian mainland. Actinella giluwensis has only bee n observed in material from Papua New Guinea. The record of A. punctata for the latter country constitutes the first confirmed record for this species outside North America and Europe. The discovery of the new Actinella speci es again confirms the importance of the Australasian region as a major cent re of microalgal biodiversity and endemism.