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Hyaloraphidium curvatum SAG235-1. Photo by Joyce E. Longcore.
Hyaloraphidium curvatum SAG235-1. Photo by Joyce E. Longcore.

Hyaloraphidium curvatum (SAG235-1) is the only member of this genus that is culturable. When it was described in 1931, H. curvatum was considered a green alga-like protist that was colorless and reproduced by the division of a single “mother” thallus into four “daughter” autospores. In 2000, a sequence derived from a culture of H. curvatum was used to construct an 18S molecular phylogeny, which aligned the species with the Chytridiomycota. Further analyses of more genetic markers refined the placement of H. curvatum in the Monoblepharidiomycetes. Hyaloraphidium curvatum is the only known member of the Chytridiomycota that has lost any ultrastructural evidence of a flagellar apparatus, though the remainder of its ultrastructural characters are similar to other taxa of the Monoblepharidomycetes. This is a holocarpic chytrid, meaning that the entire thallus of the fungus is composed of the reproductive structure, with no rhizoidal system for increased adhesive or absorptive abilities. The fungus is planktonic and in culture resembles a yeast. This extremely reduced lifecycle, even among other holocarpic chytrids that retain a reproductive lifecycle including a motile zoospore, makes H. curvatum a unique chytrid that could provide further insights into the disassembly and repurposing of genes involved in flagellation and the evolution of morphological reduction. Finally, as the most basal branch of the Monoblepharidomycetes, sequencing the H. curvatum SAG235-1 genome will allow a robust test of the deep relationships in the Chytridiomycota through phylogenomic analyses.