This paper describes the taxonomy, developmental morphology, and phylogeny of Periplasma isogametum, a new monotypic member of the Leptomitales (Oomycota). In phylogenetic trees inferred from concatenated and separate nuc 18S rDNA (18S) and nuc 28S rDNA (28S) sequences, P. isogametum forms a well-supported clade related to but distinct from Apodachlya, a member of the Leptomitales. The organism is a holocarpic facultative saprotroph of moribund aquatic insects but grows well on a variety of mycological media in which it produces large eucarpic hyphae with a peripheral layer of protoplasm surrounding a central vacuole. In zoosporogenesis, a peripheral network of zoospore initials collapses to the center of the zoosporangium and is partitioned into individual heterokont zoospores. Sexual reproduction involves morphological isogamy in which male gametes produce elongate fertilization tubes, which fuse with female gametes, which are subsequently converted into thick-walled oospores. Developmental morphology is detailed in photomicrographs and pointillism drawings.

本文介绍了异形周线虫（Leptomitales（Oomycota）的一个新的单型成员）的分类学，发育形态和系统发育。从串联和分开的nuc 18S rDNA（18S）和nuc 28S rDNA（28S）序列推断出的系统发育树中，等分对虾形成了与Apodachlya相关但与Apodachlya不同的进化枝，是Leptomitales的成员。该生物是垂死的水生昆虫的全掌兼性腐生菌，但在多种真菌学培养基上生长良好，在其中产生大量的真核菌丝，并带有围绕中央液泡的原生质外围层。在游动孢子形成中，游动孢子初始的外围网络塌陷到游动孢子囊的中心，并被分成单个的异基因游动游动孢子。有性生殖涉及形态同性一夫一妻制，其中雄配子产生细长的受精管，与雌配子融合，随后被转化为厚壁的卵子。显微照片和点画图详细描述了发育形态。