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New diatom taxa for the Indian Sundarbans found in short sediment cores

We describe, illustrate and give geographical information on 40 diatom species observed in two short sediment cores from a Holocene deposit in the Indian Sundarbans region. The Indian Sundarbans is an extremely vulnerable ecosystem that is sensitive to palaeoclimatic change. The cores were originally collected for palaeoecological reconstruction based on the analysis of diatom assemblages. The research presented here is the first step in the analysis of the subfossil diatom assemblages, which will rely heavily upon correct taxonomic identification, and is the first study of diatoms from sediment cores in this ecosystem. The present study documents 40 diatom species; 38 are new to this region. The descriptions include 11 centric species belonging to eight genera and 29 pennate species belonging to 17 genera in total. The centric diatom, Thalassiosira was the most abundant genera represented by three different species. Thalassiosira nanolineata was rarely found in the sediment from one core and not observed in the other. Tryblionella and Nitzschia were the most abundant pennate diatoms, represented by four different species each in one of the sediment cores. Diatoma moniliformis, Pseudostaurosira brevistriata, Geissleria decussis, Neidium affine, Cosmioneis pusilla, Trachyneis antillarum, Petroneis granulata and Tryblionella punctata were much less abundant species in the studied cores samples. Literature studies show that apart from two species, Actinoptychus annulatus and Thalssiosira eccentrica, 38 species have never been reported from the plankton and have also not been found previously in surface sediments of the Indian Sundarbans region. Annotated lists of the identified diatoms have been prepared along with high quality microphotographs as part of the preliminary work that will be necessary for ongoing palaeoecological reconstruction.