Baldinia droopii sp. nov. (Suessiales, Dinophyceae), a new species from a small rainwater rock pool near Tvärminne, south-western Finland

A dinoflagellate isolated from a small rainwater rockpool in Finland was found to be a new species of Baldinia , here described as B. droopii sp. nov . This is only the third formally described Baldinia species and the second described by modern methods. The new species had a complement of generic characters that clearly affiliated it to Baldinia : presence of an internal honeycomb structure, termed a lamellar body, a ventral fibre associated with the longitudinal basal body and a pentagonal resting cyst; and the absence of an apical structure, thecal plates and trichocysts. The most distinctive species-specific characters were the presence of a resting cyst with tubiform processes, a paratabulation matching the pattern of the motile cell, and a life cycle exhibiting a diel rhythm, alternating between motile and non-motile coccoid cells. Motile cells occurred during the light period, peaking after 3–4 h of light period, while practically no motile cells occurred during the dark period. LSU rDNA sequences confirmed B. droopii as a new species, showing c . 14% sequence difference compared to B. anauniensis . Asexual reproduction occurred primarily by binary fission or via a so-called division cyst. Sexual reproduction occurred in the culture indicating that D. droopii is homothallic. The zygote may form a resistant cyst with tubiform processes, but there were indications that this stage may be by-passed. Different stages of the asexual and putative sexual reproduction were observed and documented by video recordings.