Sporangium spherical, ovoid to elongate, 26-37 x 70-125 µm, frequently papillate, with elongate subsporangial swelling; rhizoid extensively branched, extending up to 240 µm; zoospore spherical to ovoid, 2.5-11.0 µm, usually uniflagellate, rarely more up to four flagella, flagella 20-30 µm long. Organelles in zoospore show weakly polarized distribution, with ovoid and spherical hydrogenosomes and nucleus in the posterior region and ribosomal aggregates in the anterior region. Zoospores contain megahydrogenosomes up to 4 µm in length. Circumflagellar rings show little tilt and do not have a C-shaped elongation. Ribosomal aggregates are always free in the cytoplasm, not embeded in homogeneous substratum.

Piromyces communi (Gold) aemulans, differt sporangiis papillatis et zoosporis megahydrogenosomaita continentibus. Intestinus equus habitat.

ETYMOLOGY: mae is named after Chinese for horse (ma) but does not necessarily imply fungus is exclusive to that host.

TYPE: Figs. 1, 3, 5-8, 10, 11, 15-16, 20-22, 25-30, 32.