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Biology LibreTexts

8.17D: Chytridiomycota - The Chytrids

Chytrids are the most primitive group of fungi and the only group that possess gametes with flagella.

 

LEARNING OBJECTIVES

 

Describe the ecology and reproduction of chytrids

 

KEY TAKEAWAYS

Key Points

 

  • The first recognizable chytrids appeared more than 500 million years ago during the late pre-Cambrian period.
  • Like protists, chytrids usually live in aquatic environments, but some species live on land.
  • Some chytrids are saprobes while others are parasites that may be harmful to amphibians and other animals.
  • Chytrids reproduce both sexually and asexually, which leads to the production of zoospores.
  • Chytrids have chitin in their cell walls; one unique group also has cellulose along with chitin.
  • Chytrids are mostly unicellular, but multicellular organisms do exist.

 

Key Terms

 

  • chytridiomycete: an organism of the phylum Chytridiomycota
  • zoospore: an asexual spore of some algae and fungi
  • flagellum: a flagellum is a lash-like appendage that protrudes from the cell body of certain prokaryotic and eukaryotic cells
  • coenocytic: a multinucleate cell that can result from multiple nuclear divisions without their accompanying cytokinesis

 

Chytridiomycota: The Chytrids

 

The kingdom Fungi contains five major phyla, which were established according to their mode of sexual reproduction or use of molecular data. The Phylum Chytridiomycota (chytrids) is one of the five true phyla of fungi. There is only one class in the Phylum Chytridiomycota, the Chytridiomycetes. The chytrids are the simplest and most primitive Eumycota, or true fungi. The evolutionary record shows that the first, recognizable chytrids appeared during the late pre-Cambrian period, more than 500 million years ago. Like all fungi, chytrids have chitin in their cell walls, but one group of chytrids has both cellulose and chitin in the cell wall. Most chytrids are unicellular; a few form multicellular organisms and hyphae, which have no septa between cells (coenocytic). They reproduce both sexually and asexually; the asexual spores are called diploid zoospores. Their gametes are the only fungal cells known to have a flagellum.

The ecological habitat and cell structure of chytrids have much in common with protists. Chytrids usually live in aquatic environments, although some species live on land. Some species thrive as parasites on plants, insects, or amphibians, while others are saprobes. Some chytrids cause diseases in many species of amphibians, resulting in species decline and extinction. An example of a harmful parasitic chytrid is Batrachochytrium dendrobatidis, which is known to cause skin disease. Another chytrid species, Allomyces, is well characterized as an experimental organism. Its reproductive cycle includes both asexual and sexual phases. Allomyces produces diploid or haploid flagellated zoospores in a sporangium.

image

Parasitic chytrids: The chytrid Batrachochytrium dendrobatidis is seen in these light micrographs as transparent spheres growing on (a) a freshwater arthropod and (b) algae. This chytrid causes skin diseases in many species of amphibians, resulting in species decline and extinction.