Chaetoceros rotosporus sp. nov. (Bacillariophyceae), a species with unusual resting spore formation

Abstract

Li Y., Lundholm N. and Moestrup Ø. 2013. Chaetoceros rotosporus sp. nov. (Bacillariophyceae), a species with unusual resting spore formation. Phycologia 52: 600–608. DOI: 10.2216/13-168.1With more than 400 species, the diatom genus Chaetoceros Ehrenberg is one of the most species-rich genera of marine planktonic diatoms. Although many Chaetoceros taxa are considered to be cosmopolitan, research has mainly focused on polar and temperate areas. Studies on material from tropical waters suggested that a high and undescribed species diversity of Chaetoceros occur here. On the basis of plankton samples collected in Daya Bay, South China Sea, a new species, C. rotosporus sp. nov., is described. Vegetative cells and resting spores were examined by light microscopy as well as transmission and scanning electron microscopy. The most variable part of the nuclear large-subunit ribosomal DNA was sequenced for information on phylogenetic relationships. Characteristic traits of C. rotosporus were a 90° rotation of the resting spore during spore maturation and a nearly rectangular silica wing that extended around the girdle of the immature resting spore. Neither character has been observed in previously described Chaetoceros species. Other distinguishing characters were the very large apertures and the single chloroplast, which formed a shallow bowl with four arms within each cell and appeared H-shaped in broad girdle view. Chaetoceros rotosporus sp. nov. belongs to the subgenus Hyalochaete Gran, but it could not be placed in any of the traditional sections of Chaetoceros, indicating a need for revision of Chaetoceros using a combination of morphological and molecular data.