Chaetoceros phuketensissp. nov. (Bacillariophyceae): a new species from the Andaman Sea

Over 400 species of Chaetoceros Ehrenberg have been described since the genus was created in 1844, making this one of the most species‐rich genera of marine planktonic diatoms. Although Chaetoceros is cosmopolitan in distribution, the temperate north Atlantic taxa are best known. Examination of material from tropical seas suggests that there are numerous Chaetoceros endemic to these biogeographic regions, which await formal description. Chaetoceros phuketen‐sis sp. nov. is described from the Andaman Sea, in the tropical Indian Ocean. It possesses several unusual morphological characteristics not found in temperate taxa, including multiple central processes on terminal valves, vermiform chloroplasts and large size. It is most similar to Chaetoceros buceros Karsten and Chaetoceros bermejensis Hernàndez‐Becerril, which also inhabit tropical seas. These taxa are not easily accommodated in the traditional classification scheme, which was based on turn‐of‐the‐century knowledge of north Atlantic taxa. Approaches for classifying these unusual species include modifications of the extant scheme and creation of a new scheme based on phylogenetic principles.