Neocallimastix: a comparative morphological study

The development from zoospore to a mature thallus in Neocallimastix sp. isolated from a Georgia cow was studied at the light microscope level. The zoospore had 9–14 posteriorly directed flagella, and its shape varied from amoeboid in agar to ovoid in broth. Encysted zoospores developed endogenously into extramatrical ovoid or spherical incipient zoosporangia with extensively branched intramatrical rhizoids that often had constrictions. Sessile mature zoosporangia varied in shape, and zoospores were fully formed within zoosporangia before release through an apical pore. In agar, zoospores encysted close to the parent zoosporangium and developed endogenously into second generation zoosporangia or exogenously into elongate thalli. At maturity, an elongate thallus was made up of a sporangium, a sporangial stalk, a cyst, and branched rhizoids. Elongate thalli were sometimes formed in broth. Melanized resting sporangia were formed on branched thalli in old (> 36 h) cultures. Two isolates of Neocallimastix front...