Trichomycetes

Definition

An obsolete, invalidly published taxonomic group of zygomycete fungi that form obligate, non-pathogenic symbioses in the hindguts of aquatic arthropods, especially insect larvae and amphipod crustaceans. Formerly treated as a class or order, these fungi are now classified in the Kickxellomycotina (orders Harpellales and Asellariales) and the Opisthokonta (orders Amoebidiales and Eccrinales).

Etymology

From Greek tricho- (hair) + mykes (fungus), referring to the hair-like, unbranched or branched thalli attached by a holdfast to the host gut lining.

Example

Harpellales such as Smittium species attach to the peritrophic matrix of black fly (Simuliidae) larvae by a secreted holdfast and extend their thalli into the gut lumen, where they likely aid in nutrient processing without harming the host.

Synonyms

• gut fungi
• arthropod gut fungi

Related Terms

• Harpellales
• Kickxellomycotina
• Zygomycota
• Symbiosis
• Hindgut
• peritrophic matrix
• Holdfast
• thallus

Usage Notes

The term persists in literature as a functional descriptor for this ecological guild, but should not be used as a formal taxon. Specialists distinguish the 'trichomycete' morphological syndrome—unbranched or branched, septate or aseptate thalli with basal holdfasts—from the polyphyletic taxonomic history. The group spans two fungal subdivisions, making it an instructive example of convergent adaptation to the arthropod gut environment. Contrast with Microsporidia, which are also intracellular or gut-associated but are now classified in the Opisthokonta as highly reduced fungi or related protists, and which are typically pathogenic rather than commensal.