Introduction to the Sagenista

Bicoecids and Slime nets

The Sagenista is a group of basal chromists. They are all heterotrophic and basically unicellular, though some live in loosely associated colonies. The group has no characters that unite it, and so the group is generally believed to be paraphyleitc, though the details of relationships are not yet known. Sagenista includes two major groups of organisms, including one that has been classified with the fungi, and one that has only recently been recognized.

The first group are the Bicoecea, a small collection of poorly studied unicells. Some of these have been known for more than a century, while others have only recently been described. One of the more exciting recent discoveries is the species Cafeteria roenbergensis. This species is actually quite common, and feeds indiscriminantly on whatever it can find (and hence its name).

A second group, the Labyrinthulomycota, or slime nets, have traditionally been grouped with the slime molds, but are now believed to be part of the Chromista. The slime nets have become the subject of much recent investigation because they are now known to cause a disease that kills sea grass (Zostera). It has also been discovered that they have an organelle called a bothrosome that is capable of secreting a membrane outside their cells. The membranes produce a network of filaments along which the cells can travel. They appear to be unique in this ability.

Both groups of Sagenistans have flagellated stages with two dissimilar flagellae like other chromists. It is believed that they are relicts of the earliest chromistan evolution, and may represent something of what the ancestral members looked like.

For more information about bicoecids such as Cafeteria and Caecitellus, visit the Protist Image Database at the University of Montreal.

Or read an article about how the slime net Labyrinthula parasitizes sea grass in the Everglades, an article by the National Park Service.