The Labyrinthulomycota is comprised of three distinct lineages

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