Pseudulvella americana (Snow) Wille belongs to the order Chaetopeltidales (Class Chlorophyceae), evidence from ultrastructure and SSU rDNA sequence data

SÁNCHEZPUERTA VIRGINIA; LEONARDI PATRICIA; OKELLY CHARLES; CÁCERES EDUARDO

JOURNAL OF PHYCOLOGY

Phycological Society of America

Lugar: Malden; Año: 2006 vol. 42 p. 943 - 950

0022-3646

The genus Pseudulvella Wille 1909 includes epiphytic, freshwater or marine disc-shaped green microalgae that form quadriflagellate zoospores.  No ultrastructural or molecular studies have been conducted on the genus, and its evolutionary relationships remain unclear.  The purpose of the present study is to describe the life history, ultrastructural features and phylogenetic affiliations of Pseudulvella americana (Snow) Wille, the type species of the genus.  Thalli of this microalga were prostrate and composed of radiating branched filaments that coalesced to form a disc. Vegetative cells had a pyrenoid encircled by starch plates and traversed by one or two convoluted cytoplasmic channels.  They had well-defined cell walls without plasmodesmata.  Asexual reproduction was by means of tetraflagellate zoospores formed in numbers of 2-8 from central cells of the thallus. The flagellar apparatus of zoospores was cruciate, with four basal bodies and four microtubular roots.  The paired basal bodies lay directly opposite (DO) one another.  The microtubular root system had a 5-2-5-2 alternation pattern, where the “s” roots contained five microtubules in a four-over-one configuration.  A tetralobate non-striated distal fiber connected all four basal bodies.  A wedge-shaped proximal sheath subtended each of the basal bodies. The ultrastructural features of the zoospores were those of members of the order Chaetopeltidales.  Phylogenetic analyses based on SSU rDNA placed Pseudulvella americana sister to Chaetopeltis orbicularis in a well supported Chaetopeltidales clade. Such a combination of features confirmed that this alga is a member of the order Chaetopeltidales. Key words: Chaetopeltidales, Chlorophyta, life history, phylogeny, Pseudulvella, ultrastructure.