THALASSIOSIRA ANDAMANICA SP. NOV. (BACILLARIOPHYCEAE), A NEW DIATOM FROM THE ANDAMAN SEA (THAILAND)

Abstract

A new marine diatom, Thalassiosira andamanica, is described from light and electron microscopy. The specimens were collected in the vicinity of Phuket Marine Biological Center, Thailand, and later brought into clonal culture. Thalassiosira andamanica possess a rimoportula with a pronounced outer extension, one marginal ring of fultoportulae, and three rings of fultoportulae on the valve face. Cells are united into colonies by a single thread secreted through a central fultoportula. Marginal fultoportulae extensions are shortest on the inside of the valve. The areolae are arranged in sectors, and the valve margin is ribbed with approximately 38 ribs in 10 μm. The valvocopula and copula have rows of pores, four to six pores in 1 μm. Apparently, the pleurae are hyaline. Experiments with a clonal culture isolated at Phuket, Thailand, showed that growth (cell divisions·24 h−1) was reduced for cultures grown at 14° C compared to those grown at 19°, 24°, or 30° C. The maximum growth rate (2.2 divisions·24 h−1) was at 30° C. Thalassiosira andamanica is compared with morphologically similar taxa. On the basis of morphological features and the response to different temperature regimens, it is concluded that this taxon must be recognized as a new warm‐water species. In addition, T. andamanica does not clearly belong to any of the two subgroups of species of Thalassiosira. To accommodate the morphological characteristics of T. andamanica, the establishment of a possible third subgroup is discussed.