Labyrinthulomycetes
Labyrinthulomycetes (ICBN), Labyrinthulea (ICZN) or labyrinthulids is a group of protists that form colonies and produce a network of filaments or tubes that serve as tracks for cells to glide over them and absorb nutrients. They are mostly of marine origin, commonly found as parasites of algae or decomposing plant matter. They also include some parasites of marine invertebrates. In all, about 40 species are known in this group.
Cells are attached to filaments that form part of an ectoplasmic network. Although located on the outside of the cells, the filaments are surrounded by a membrane. These are formed and are connected to the cytoplasm by a unique organelle called the sagenogen or botrosome. Cells are uninucleate and typically ovoid and move back and forth along the amorphous network at a rate of 5–150 μm per minute.
Labyrinthulids were initially considered unusual myxomycetes, although the two groups are actually quite different. The structure of their biflagellate zoospores and genetic studies have established that they constitute a primitive group of Heterokontophyta. The group is divided into three orders, Amphitremida, Labyrinthulida (which form extensive webs) and Thraustochytrida (which form small webs).