An SEM study of Peridiniella sphaeroidea and P. catenata (Dinophyceae)

Summary

The thecal plates of Peridiniella sphaeroidea from the Atlantic Ocean and P. catenata from the Baltic Sea have been studied by scanning electron microscopy. In both, the basic plate formula is Po, 4′, 3a, 7″, c, s, 6⃛', lp, l′⃛' but P. catenata has a small extra intercalary x-plate. There are major differences between the species in their shape, ornamentation (antapical spines in P. catenata), and appearance of the thecal plates (a strongly marked pattern in P. sphaeroidea, smooth in P. catenata). In terms of their ecology P. sphaeroidea comes from warm, high-salinity water and P. catenata is found in cold low-salinity water. However, there are good reasons for keeping these two distinctive organisms within the same genus and Peridiniella is the most appropriate one at present.