Ultrastructure and Phylogeny of Kirithra asteri gen. et sp. nov. (Ceratoperidiniaceae, Dinophyceae) - a Free-Living, Thin-Walled Marine Photosynthetic Dinoflagellate from Argentina.

A gymnodinioid photosynthetic dinoflagellate was isolated from Argentina and examined by light and electron microscopy and analysis of nuclear-encoded LSU rDNA. Kirithra asteri gen. et sp. nov. was proposed as morphology and molecular phylogeny separated this dinoflagellate from others within the family Ceratoperidiniaceae. Cells were surrounded by a hyaline amphiesma comprising polygonal vesicles. Each vesicle contained a honeycomb and a trilaminar structure. An anterior sulcal extension ending in a complete circle formed the apical structure complex (ASC), which characterizes Ceratoperidiniaceae. The ASC comprised three rows of vesicles. The nucleus was located in the hypocone, and several large, irregularly shaped vesicles were present in the epi- and hypocone. Chloroplasts were surrounded by three membranes, and grana-like arrangements of thylakoids were observed in one strain used for ultrastructural study. The cell centre contained 1-3 multiple-stalked pyrenoids and membrane-bound vesicles containing tile-like structures surrounded each pyrenoid. Two pusules with collecting chambers and associated vesicles branched off each of the flagellar canals. The flagellar apparatus featured a ventral connective between the amphiesma and the R1 root, and almost opposite basal bodies, rarely seen in dinoflagellates. This was the first ultrastructural study of a species within Ceratoperidiniaceae.

Loricate Choanoflagellates from the South Atlantic coastal zone (~32 ºS) including the description of Diplotheca tricyclica sp. nov / Choanoflagelados Loricados da zona costeira do Atlântico Sul (~32 ºS) incluindo a descrição de Diplotheca tricyclica sp. nov

The biodiversity of marine heterotrophic protists is poorly known in the South Atlantic coastal zone (~32 ºS) especially regarding the nanoflagellates. The presence of loricate choanoflagellates was reported for the first time in the Patos Lagoon estuary and the adjacent coastal zone. Seventeen species of eleven genera of loricate choanoflagellates were observed between October 1998 and May 2000 in fixed water samples (lugol's solution + glutaraldehyde) in a JEM 100-SX transmission electron microscope. Most species were recorded in euhaline and mixopolyhaline waters during the spring and summer, none in autumn and a few (four) in winter. The absence of choanoflagellates at the more sheltered inshore stations is due freshwater influence, and at the beach station, probably due the strong wave action. The probably cosmopolitan species Pleurasiga minima, Cosmoeca norvegica, C. ventricosa and Parvicorbicula circularis were present in spring or summer in the estuary channel and coastal area while Stephanoeca diplocostata which apparently prefers lower temperature, was recorded in winter. Calotheca alata and Campyloacantha spinifera are mainly temperate species and were present in spring. The new species Diplotheca tricyclica was recorded at the estuary channel in the summer 1999, in high salinity water.

A biodiversidade de protistas heterotróficos é pouco conhecida na zona costeira do Atlântico Sul (~32 ºS), especialmente dos nanoflagelados. No presente estudo, foi registrada pela primeira vez a presença de coanoflagelados loricados no estuário da Lagoa dos Patos e na zona costeira adjacente. Dezessete espécies de onze gêneros de coanoflagelados loricados foram observadas em amostras de água fixadas (solução de lugol + glutaraldeido) coletadas entre outubro de 1998 e maio de 2000, e analisadas em microscópio de transmissão JEM 100-SX. A maior parte das espécies foi registrada em águas euhalinas e mixopolihalinas durante a primavera e o verão, nenhuma no outono e poucas (quatro) no inverno. A ausência de coanoflagelados nas estações mais protegidas deve-se a influência da água doce, e na estação da praia deve-se, provavelmente, a forte ação das ondas. As espécies, provavelmente cosmopolitas, Pleurasiga minima, Cosmoeca norvegica, C. ventricosa and Parvicorbicula circularis ocorreram na primavera ou no verão no canal principal do estuário e na área costeira, enquanto Stephanoeca diplocostata, que aparentemente prefere baixas temperaturas, foi registrada no inverno. Calotheca alata e Campyloacantha spinifera são principalmente de ambientes temperados e estiveram presentes na primavera. Uma espécie nova, Diplotheca tricyclica, foi registrada na área do canal principal do estuário, no verão de 1999, em águas de alta salinidade.