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Cirri are curled appendages borne on the surface of mature zygotes in some members of the green algal family Sphaeropleaceae. Structures equivalent to cirri have not been reported previously in any green algae. We found cirri in four taxa: Sphaeroplea fragilis Buchheim et Hoffman, Atractomorpha porcata Hoffman, and two new undescribed species of Atractomorpha from Africa. Zygotes of seven other sphaeropleacean taxa were examined, but they did not produce cirri. Cirri may be either simple or compound. Simple cirri are less than 0.5 μm in diameter and show no evidence of longitudinal striations or subunits. Compound cirri are more massive (commonly 2.0-3.5 μm, and up to 4 μm diameter in S. fragilis) and possess longitudinal striations suggesting that each is formed of longitudinally arranged subunits ca. 0.5 μm in diameter. Simple and compound cirri are formed by zygotes of all four tax that produce cirri. Both types may occur on the same zygote. Nonetheless, the patterns of variation in length, shape, and distribution of the two types of cirri are sufficiently distinct to characterize each taxon. Energy dispersive X-ray microanalysis (EDX) shows that cirri lack appreciable mineralization and are thus primarily organic in nature. The potential value of cirri as a taxonomic character in the Sphaeropleaceae is discussed. [ABSTRACT FROM AUTHOR]

Atractomorpha echinata gen. et sp. nov. is described from isolates derived from zygotes present in a dry soil sample obtained from Texas. The new genus is distinguished from Sphaeroplea primarily by its pattern of vegetative growth. While Sphaeroplea is distinctly filomentous with numerous coenocytic cells uniseriately arranged. Atractomorpha grows as individual, multinucleate, spindle-shaped cells with sharply pointed extremities. Such cells may vary considerably in length (25-6000 μm. or more) and normally lack sepita. In young, rapidly growing cultures the cells often attain lengths of 300-500 μm. but rarely exceed 1800 μm. The new spices is further characterized by: (1) the regular formation of biflagellate zoospores in asexual reproduction, (2) anisagamy (occasionally oogamy) and (3) the size and ornamentation of its zygotes. Variations in vegetative morphology are discussed as are conditions for obtaining gametogenesis. [ABSTRACT FROM AUTHOR]