Prevalence history of morphological variants of Cerataulina resting spores in Indian Sundarbans and resultant phylogenetic analysis

Fifteen morphological variants of resting spores of the diatom Cerataulina are presented with morphometric characters and presence in different habitats over spatial and temporal regimes in the Indian Sundarbans. Spatial regime includes phytoplankton assemblages, river-bank surface sediments and different depths of short sediment cores of adjacent deltaic landmasses. The temporal regime spans a period of 2000 years BP to present times. Though Cerataulina is sporadically mentioned in a few publications as a planktonic form in the Sundarbans, this is the first report of its different resting spores from different habitats. The 14C dating and calculated age within sediment cores suggest their existence in the system for 1996 years BP. Interestingly, even with the significant prevalence of resting spores throughout the spatial and temporal ranges, the live vegetative stage could only occasionally be documented in the phytoplankton assemblages over a period of 9 years from February 2013 to March 2023. The morphological variations of Cerataulina resting spores were subjected to cluster analysis using Dice’s Similarity Coefficient, based on the unweighted pair group method with arithmetic mean to indicate phylogenetic relationships. The results highlight two main clusters of resting spore morphotypes, namely Cerataulina bicornis (syn = Cerataulina daemon) and Syringidium simplex.