Kathablepharida

The kathablepharids or katablepharids () are a group of heterotrophic flagellates closely related to cryptomonads. First described by Heinrich Leonhards Skuja in 1939, kathablepharids were named after the genus Kathablepharis. This genus is corrected to Katablepharis under botanical nomenclature, but the original spelling is maintained under zoological nomenclature. They are single-celled protists with two anteriorly directed flagella, an anterior cytostome for ingesting eukaryotic prey, and a sheath that covers the cell membrane. They have extrusomes known as ejectisomes, as well as tubular mitochondrial cristae.

==Evolution== {{cladogram| |caption=Relationships between katablepharids and closely related protists. Hacrobian taxa marked with asterisks. }} Besides the known katablepharid diversity, dozens of environmental DNA sequences (both freshwater and marine) seem to represent further katablepharids which have not been cultured or formally described. Through molecular phylogenetic analyses, they are consistently recovered as the sister clade to cryptomonads, an assemblage of flagellates containing the phagotrophic goniomonads and the photosynthetic cryptomonads. Initially, both groups were placed in the Hacrobia, a tentative group that also contained haptophytes, centrohelids, biliphytes and telonemids. However, the Hacrobia hypothesis was later disproven. Instead, haptophytes and centrohelids belong to the phylum Haptista, while cryptomonads and katablepharids remain as sister groups within the phylum Cryptista together with Palpitomonas. Haptista is more closely related to the TSAR clade, which includes telonemids, while Cryptista is more closely related to the Archaeplastida clade, which includes red algae, green algae, plants, glaucophytes and biliphytes.