| Summary: | Coolia is a widespread and ecologically important
genus of benthic marine dinoflagellates found in
tropical regions. Historically, there has been
taxonomic confusion about the taxonomy and
toxicity of this group. The goal of this study was to
resolve morphological questions concerning Coolia
tropicalis and determine the taxonomic identity of the
Australian Coolia isolate which has been reported to
produce cooliatoxins. To accomplish this, the
morphology of tropical strains from Belize (the type
locality of C. tropicalis), Malaysia, Indonesia, and
Australia were examined and compared to published
reports. The morphological analysis showed that
C. tropicalis differs from the original description in
that it has a slightly larger size (35–47 lm long by
30–45 lm wide versus 23–40 lm long by 25–39 lm
wide), and the shape of fourth apical plate, and the
length of Po plate (7.4–12 lm versus 7 lm). Based
on both morphology and phylogenetic analysis using
LSU D1- D3 rDNA sequences, the clones of
C. tropicalis from Malaysia, Indonesia, and Belize
were found to form a monophyletic clade within the
genus. The strain producing cooliatoxin was found to
be C. tropicalis, not Coolia monotis as originally
assumed. To explore the factors influencing the
growth of Coolia species, the growth rates of
C. tropicalis and Coolia malayensis were determined at
different temperatures and salinities. Both species
tolerated a wide range of temperatures, but cannot
survive at temperatures <20°C or >35°C. C. monotis,
the dominant species reported in the literature,
probably does not produce toxins.
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