Hyphae vegetativae delicatae. Zoosporangia elongata; zoosporae emissae, ex orificio zoosporangium natantes; zoosporangia seconda intra prima vel subter vel latere formata. Zoosporae monoplaneteace. Oogoniis copiosis, sphaericis, vel plures papillas habentibus, ant irregularibus; 17.5-30 μ in diam., plerumque 20-25 μ excl, papillis. Tunica oogoniorum non-punctulate. Oosporis 15-(17.5-22)-25 μ, sphaericis, subcentricae vel centricae, quae singualis in oogoniis. Ram antheridiales sunt rarissimo, et tunc sunt androgyini, quroum antheridia, non exurgunt immediate post oogonium. Vegetative hyphae slender, much branched, 9-30 μ in diametes, thickest at the terminal. Zoosporangia rare or moderately abundant; elongate; 100-450 × 20-30 μ; sporangia renewed by lateral branches, rarely internal proliferation. Zoospores discharge saprolegnoid, pip shaped with two apical cilia, sprouting by germ-tube after the first encystment (monomorphic). Gemmae rare or moderately abundant, spherical, elongate or irregular; single or catenulate. Oogonial wall thin, unpitted and more or less papillate; 30-(25-20)-17.5 μ exclusive of papillae. Immature oogonia possessing a conspicuous mucilage layers. Oosphere maturing. Oospores subcentric, rarely centric; one in the oogonium, 15-(17.5-22)-25 μ in diameter. Antheridial branches very rare, if any, androgynous, antheridial branches not arising from immediately below the oogonium.
Specimens：
Type locality: Taipei, Shih-lin; compost; Oct 15, 1973.Type specimen: type culture is deposited in the herbaria of the Institute of Botany, Academia Sinica.
Habitat：
Soil and water
Distribution：
Shih-lin, Taiwan
References：
Hohnk NV. 1952; Sparrow FK Jr. 1960.
Provided：
T. S. Chiou and H. S. Chang
Note：
H?hnk (1952) erected a new genus Aplanopsis with one species A. terrestris, and Dick (1960) established a new species A. spinosa by spiny oogonial wall. However, no species of Aplanopsis produced asexual reproduction, therefore, Aplanopsis was not complete as Sparrow (1960) suggested. Recently we collected an isolate of this genus. We found that the isolate formed many zoosporangia on hempseed in water two days after cultivation at 20℃ under light condition. Some sporangia grew from slender of stouter hyphae. Hyphae were thicker in the neighborhood of sporangia. Sporangia renewal was by sympodial branches, rarely by internal proliferation. Zoospores are pear shaped, with two terminal flagellates. They leave from the mouth and swim away. At higher temperature such as 25℃ they soon became encysted. Cysts are 9-12 μ in diameter, predominantly 10 μ and did not form secondary zoospores at 10℃ to 25 ℃. The presence of monomorphic zoospore, saprolegnoid zoospore discharge and a conspicuous mucilage layers in immature oogonial wall, indicate that our isolate, in fact, is a species of the genus Pythiopsis. So Aplanopsis terrestris H?hnk is only a strain of Pythiopsis terrestris without asexual reproduction. P. terrestris can be distinguished from Aplanopsis spinosa Dick (1960) only by having papillate oogonial wall instead of spiny one. However, until the zoosporangia can be ovserved, A. spinosa will still remain as an imperfectly known species. P. terrestris can also easily be distinguished from other species of Pythiopsis by subcentric oospore structure instead of subeccentric type. Moreover, antheridial branches were often absent in our isolate. So we erected it P. terrestris as a new species of Pythiopsis.
Phylum：Oomycota >> Class： Oomycetes >> Order： Saprolegniales 
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