A LIGHT AND ELECTRON-MICROSCOPIC STUDY OF THE DIATOM AULACODISCUS-PETERSII EHRENBERG, FROM NEW-ZEALAND COASTAL MARINE HABITATS AND IDENTIFICATION OF THE HOLOTYPE

Aulacodiscus petersii Ehrenberg is widely distributed in coastal marin e habitats of North Island, New Zealand (N. Z.), but has not been reco rded from South Island. Specimens from Barbados (fossil), Cape Verde I slands, Madagascar and Veracruz have been examined and compared with N . Z. specimens from my recent gatherings. These specimens were compare d with light micrographs of the specimen recently identified as the ho lotype and the drawing in the Ehrenberg Collection. The holotype and d rawing are so unambiguous that the species currently known as A. peter sii is now confirmed as being A. petersii Ehrenberg. Aulacodiscus pete rsii var. asperula Rattray and A. petersii var. notabilis Rattray cann ot be distinguished as separate varieties within the species. Studies of A. petersii by light microscopy (LM) and scanning electron microsco py (SEM) revealed many similarities to other species of this genus, pa rticularly in the structure of the loculate areolae and tubular proces ses. Aulacodiscus petersii also shows similarities in SEM to some spec ies of Coscinodiscus.