Haptoglossa is an enigmatic protistan genus provisionally placed in the phylulm Oomycota (Order Saprolegniales, Family Ectrogellaceae). Consisting of about seven species, members of this unique taxon are commonly found in manure piles and herbivore dung as obligate parasites of bactivorus nematodes and rotifers. The most commonly infected nematode hosts include the genera, Rhabditis and Bunonema. Some species produce motile biflagellate zoospores with smooth flagella as a part of their life cycle while others have been described as being "aplanosporic" meaning that they do not produce zoospores. Their morphology like many other protists is simple. The thalli are oblong, following the morphology of the host, and holocarpic in form. Discharge tubes become prominent at maturity and rupture through the host cuticle in order to release zoospores into the environment. Once the zoospores are released, they swim around for a short amount of time before settling down and encysting. The cyst then develops into what is called a "gun cell". The uninucleate gun cell when brushed by a grazing rotifer or nematode, fires and injects its protoplast called the "sporidium" into the host. The sporidium will then develop into a single holocarpic thallus. So far no one has discovered a sexual stage (no oospores) or any kind of resting spore for any of the species, leaving the life cycle incomplete. Characters which have been used to separate out the species include: spore morphology and structure (Aplanosporic species) and variations in gun cell structure (Zoosporic species). According to Beakes and Glockling, due to their overall cell structure and zoospore ultrastructure, members of Haptoglossa belong within the Stramenopile group but may represent a separate class based on their lack of oogamy and the unique infection cells.
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