thumb|[[Heterokont zoospore of Saprolegnia with tinsel and whiplash flagella.|271x271px]]

A zoospore is a motile asexual spore that uses a flagellum for locomotion in aqueous or moist environments. Also called a swarm spore, these spores are created by some protists, bacteria, and fungi to propagate themselves. Certain zoospores are infectious and transmittable, One common feature of zoospores is their asymmetrical shape; a result of the ventral groove housing the flagella base. Certain zoospores progress through different phases, the first phase commonly referred to as 'the initial'. illustrated in Fig. 1 at right:

  1. Posterior whiplash flagella are a characteristic of the Chytridiomycota, and a proposed uniting trait of the opisthokonts, a large clade of eukaryotes containing animals and fungi. Most of these have a single posterior flagellum (Fig. 1a), but the Neocallimastigales have up to 16 (Fig. 1b).
  2. Anisokonts are biflagellated zoospores with two whip types flagella of unequal length (Fig. 1c). These are found in some of the Myxomycota and Plasmodiophoromycota.
  3. Zoospores with a single anterior flagellum (Fig. 1d) of the tinsel type are characteristic of Hyphochytriomycetes.
  4. Heterokont are biflagellated zoospores (Fig. 1e, f) with both whiplash (smooth) and tinsel type (fine outgrowths called mastigonemes) flagella attached anteriorly or laterally. These zoospores are characteristic of the Oomycota and other heterokonts.

Zoosporangium

thumb|209x209px|Zoosporangia and zoospores of Phytophthora agathidicida

A zoosporangium is the asexual structure (sporangium) in which the zoospores develop in plants, fungi, or protists (such as the Oomycota). Developing sporangia of oomycetes go through a process of cleavage in which a protein kinase, in the case of Phytophthora infestans, induces the sporangial cytoplasm to split and release the various zoospores. Release of the spores can occur either inside of the zoosporangium (intrasporangial zoosporogenesis) or exteriorly (extrasporangial zoosporogenesis). Others may utilize species of frogs (such as Bufo marinus and Rana catesbieana) as carriers, allowing extended ranges of travel.