Two new species of the dinoflagellate genus Phalacroma Stein (Dinophyceae) from the tropical Mexican Pacific

摘要

Species of the thecate dinoflagellate genus Phalacroma Stein are common in the marine phytoplankton all over the world, but especially diverse in tropical areas. Some species are considered to produce Okadaic Acid or Dinophysistoxin, which cause diarrhetic shellfish poisoning (DSP). The genus Phalacroma includes mixotrophic and heterotrophic species with an elevated epitheca, visible in lateral view and narrow horizontally projected cingular lists. During surveys of phytoplankton from the tropical Mexican Pacific, two undescribed species of Phalacroma were found, and in this paper they are depicted following detailed observations by LM and SEM. Phalacroma ornamentatum sp. nov. is a new species, superficially similar to species of the Phalacroma rotundatum (Claparede et Lachmann) Kofoid et Michener group, but its main distinctive characteristics are: (1) epitheca considerable domed, (2) theca particularly thick, (3) strong ornamentation of theca and sulcal lists, and (4) relatively narrow sulcal lists and their junction close to the cingulum. The other new species is Phalacroma palmaturn sp. nov., which is distantly similar to Phalacroma bipartinun Kofoid et Skogsberg, and is characterized by (1) shape and extension of the left sulcal list to the posterior part of cell, (2) absence of R2 in the left sulcal list, (3) sulcal lists joined at the cingulum level, and (4) ornamentation pattern of the theca and both sulcal lists. Phalacroma omamentatum was fairly common in the Gulf of California, whereas Phalacroma pahnatum was very rare.