The Labyrinthulomycota is comprised of three distinct lineages

The labyrinthulids and thraustochytrids, identified by the presence of bothrosomes and the associated ectoplasmic net, are marine saprobes classified as stramenopiles in the kingdom Protista. We have sequenced a partial ssurDNA region for 10 isolates in five genera, including Diplophrys marina (a possible labyrinthulid relative which lacks bothrosomes). We also include sequences of two isolates of the northern quahog pathogen, QPX, a thraustochytrid of uncertain taxonomic affinities. Our ssurDNA sequence analysis indicates that members of the Labyrinthulomycota fall into three phylogenetic groups. These groups correspond to the three morphological extremes found within the phylum; the labyrinthulids, the thraustochytirds, and the labyrinthuloids. QPX sequences support its inclusion as a thraustochytrid. Diplophrys marina also appears to show phylogenetic affinity with the thraustochytrids.