What is "chaetoceros"

Chaetoceros is probably the largest genus of marine planktonic diatoms with approximately 400 species described, although a large number of these descriptions are no longer valid. It is often very difficult to distinguish between different Chaetoceros species. Several attempts have been made to restructure this large genus into subgenera and this work is still in progress. However, most of the effort to describe species has been focused in boreal areas, and the genus is cosmopolitan, so there are probably many tropical species still undescribed.