Hexamita (hex-a-mite-a), a free living diplomonad flagellate. Diplomonads are so-called because most members of the group have two nuclei, and have clusters of up to 4 flagella emerging from opposing sides of the cell. They arise in grooves, which are believed to correspond to the ventral grooves of the excavate flagellates. Normally associated with anoxic habitats. Diplomonads are probably best known because one their members, Giardia, is significant as a parasite of the intestinal system, and because it is prominent in studies on the evolution of eukaryotic cells - "clinging resolutely" to the base of the eukaryotic tree as our best candidate for the most primitive eukaryote. The two nuclei are at the anterior (top) and the junction between them is seen as a dark line. The flagellar grooves and some of the flagella are evident. Phase contrast. This picture was taken by David Patterson, Linda Amaral Zettler and Virginia Edgcomb of material from the salt marsh at Little Sippewissett (Massachusetts, USA) in Autumn, 2000 and in Spring and summer, 2001. Image copyright: D. J. Patterson, L. Amaral-Zettler and V. Edgcomb, image used under license to MBL (micro*scope).
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From the collection
Little Sippewissett salt marsh, Massachusetts, USA
|Description of Hexamita: Hexamatine diplomonad flagellates, oval or pyriform cell body (6-35µm), truncated or tapered posteriorly, bearing 6 anterior locomotory flagella and 2 posterior trailing ones; 2 rounded nuclei closely apposed each other at the anterior end; recurrent flagella traverse the cell to emerge posteriorly as trailing flagella and lie in longitudinal canals which open posteriorly forming 2 apertures which are the cytostomes of the cell; many species live in freshwater and saltwater rich in organic matter and bacteria, preferring low oxygen sites; form cysts; parasitic species occur in insects, in oysters, in salmonid fishes, in the cloaca of reptiles, in the coecum of rodents, in monkeys H. pitheci etc. but parasitic Hexamita species and Spironucleus species are difficult to distinguish. |