SYSTEMATIC BIOLOGY					THE HETEROKONTAE
HOME	SYLLABUS	WEEKLY ASSIGNMENTS	J. SYSTEMATIC BIOLOGY	TAXA OF LIFE
PHYLUM LABYRINTHULOMORPHA

INTRODUCTION TO THE LABYRINTHULOMORPHA

Labyrinthulomorpha (la-ba-RIN-thu-lo-MOR-fa) is derived from a Latin root  that means little labyrinth (labyrinthulum) and a Greek root meaning form (morphe -μορφή).  The reference is to the intricate slime nets that they produce and move through.

The slime nets are fungus-like organisms that mainly are known for attacking sea grasses.  Labyrinthula (Figures A&B) lives as a collective of spindle-shaped cells within an anatomizing web of slime tubes which are formed by specialized organelles called bothrosomes (sagenetosomes).  The cells move freely through the tubes, but cannot move at all if removed from them.  Despite their fungus-like appearance, they do produce typical heterokont zoospores (meiospores) that function in dispersal.  The slime nets are important because of their negative impact on eel grass (Zostera marina), an important member of Chesapeake Bay and other brackish and marine environments.  More recently, labyrinthulids have begun to be implicated as the causative agents of turf grass diseases, particularly on golf greens.

A. A low power view of  Labyrinthula cells within the slime net.	B. An SEM micrograph of a spindle-shaped Labyrithula cell outside of its slime tube.
Images taken from: A: http://microscope.mbl.edu/baypaul/microscope/images/t_imgAZ/labyrinthula_epw.jpg B: http://people.uncw.edu/durakom/FHAP/LabySEM.jpg

SYNOPTIC DESCRIPTION OF THE LABYRINTHULOMORPHA

SYSTEMATICS OF THE LABYRINTHULOMORPHA

The affinities of the Labyrinthulamorphs have been misunderstood, mainly because they were defined by essentialist arguments like: they feed like slime molds, therefore they must be related to slime molds.  However, the recognition that they are related to other heterokonts (e.g. Patterson, 1989) finally gave them a home and set them apart from the slime molds.Older manuals like Grell (1973) and Kudo (1966) assigned the labyrinthulids to taxa of uncertain status.  However, because of their unusual cellular organelles (e.g. bothrosomes) and odd means of locomotion, later manuals [e.g. Pokorny (1985), Sleigh et al.(1984) and Margulis and Schwartz (1988, Pr-21; 1998, Pr-18)] indicated that the labyrinthulids clearly required phylum-level ranking. Alexopoulos and Mims (1979) assigned them to the slime molds. Although Pokorny (1985) did not group the thraustochytrids together with the labyrinthulids, Porter (1990) united them within the same phylum because they both produced the same kind of motile cell and both had bothrosomes. 

Patterson (1989) proposes that the motile cells of the labyrinthulids suggest a connection with the chrysophyte complex. A lipid structure in the zoospore might be homologous to the eyespots of organisms like the eustigs. Porter (1990) simply acknowledges that phylogenitic affinities are not known.  Leipe et al. (1995) in a study of molecular phylogeny place them together with other heterokonts (also acknowledged and followed by Patterson, 1999).  Sogin and Patterson (Tree of Life Project) and Baldauf (2003) placed the labyrinthomorphs near the base of the heterokont tree.

HIERARCHICAL CLASSIFICATION OF THE LABYRINTHULOMORPHA

This page is maintained by Jack R. Holt. Last revised 02/20/2008 .