Rufus H. Thompson

SEXUAL REPRODUCTION IN CHAETOSPHAERIDIUM GLOBOSUM (NORDST.) KLEBAHN (CHLOROPHYCEAE) AND DESCRIPTION OF A SPECIES NEW TO SCIENCE

Developmental morphology and sexual reproduction of Chaetosphaeridium globosum are described. Dicoleon nordstedtii is reduced to synonymy with C. globosum. A species new to science, C. gemmatum, is described. Descriptions are given of material collected of C. ovalis and C. pringsheimii accompanied by a key to the 4 species of the genus. The species C. huberi is relegated to species dubium.

The Chrysophyte Genera Synuropsis Schiller, Volvochrysis Schiller, Synochromonas Korshikov, Pseudosynura Kisselew, Pseudosyncrypta Kisselew, Chrysomoron Skuja, and Syncrypta Ehrenberg

Abstract A revision of the chrysophyte genus Synuropsis Schiller is proposed and its taxonomic status is validated. The closely related genera Volvochrysis Schiller, Synochromonas Korshikov, Pseudosynura Kisselew, Pseudosyncrypta Kisselew, and Chrysomoron Skuja are reexamined and placed in synonymy with Synuropsis. A key to the six species now recognized of Synuropsis is given.

The genera Uroglena, Uroglenopsis, and Eusphaerella (Chrysophyceae)

Abstract Distinctive features that support the retention of Lemmermanns genus Uroglenopsis and distinguish it from Ehrenbergs Uroglena are presented. In Uroglena, the cells are united by a branching system of cytoplasmic threads, which is produced as cells divide and separate, the cells have a pointed posterior end because of attenuation to the diameter of the connecting thread, and the whip flagellum is approximately one-half the length of the long pleuronematic flagellum. In Uroglenopsis, the cells are united by a branching system of gelatinous stalks, the cells are truncate at the posterior end, and the whip flagellum is at the most one-quarter the length of the long flagellum. A key to species is given and statospores of all species are illustrated. The close relationship of Skujas Eusphaerella to these genera is explored.

Chrysocapsopsis rupicola: A new genus and species in the Chrysophyceae

Chrysocapsopsis rupicola gen. et sp. nov. (Chrysophyceae) is described. It differs from Chrysocapsa and the closely related genera Chrysocapselia and Tetrachrysis by possessing both epiphytic and planktonic forms within the same life‐history. Reproduction is by budding which produces short irregular branches within a gelatinous mass. Four or more aplanospores are produced from each mother cell; no motile cells were observed.

Endophytic unicellular chlorophytes: a review of Chlorochytrium and Scotinosphaera

D.E. Wujek and R.H. Thompson. 2005. Endophytic unicellular chlorophytes: a review of Chlorochytrium and Scotinosphaera. Phycologia 44: 254–260. The genera Nautococcopsis and Ectogeron are reduced to synonymy with Chlorochytrium. The inclusion of Scotinosphaera and Kentrosphaera within the genus Chlorochytrium is considered now untenable. Scotinosphaera and Kentrosphaera are considered synonymous, with the name Scotinosphaera having priority. Redefinitions are given for Chlorochytrium and Scotinosphaera based on seven opposed attributes. Chlorochytrium, in germination of the zoospore, secretes an attachment disc; has fundamentally a parietal chloroplast that develops many radiate lobes, few to many pyrenoids; and the vegetative cell contains few to many minute contractile vacuoles. Its first two to four divisions are vegetative. Further division of each protoplast results in biflagellate zoospores that are walled, compressed and have a flagellar papilla. Scotinosphaera lacks an attaching disc; is strictly unicellular with no vegetative divisions; contains an axile chloroplast with many radiate arms; has characteristically one large central pyrenoid; lacks contractile vacuoles; and division results in numerous biflagellate, terete, spindle-shaped zoospores. Old cells may develop one or more localised lamellated, wart-like thickenings of the wall, externally or internally. Sexual fusion has been observed for Chlorochytrium but not for Scotinosphaera. The relationships of Chlorokoryne, Eremotyle, Nautococcus and Excentrosphaera are reviewed.

Cleavage pattern of Volvox aureus (Volvocales)

Abstract Historical and recent reports on Volvox aureus have not satisfactorily explained cellular differentiation and development in this organism. The diagrammatic illustrations in these reports fail to accurately depict the division pattern of the developing embryo. In reinterpreting Volvox embryogenesis, the dextral spiral adjustment which occurs between each cell division can be identified as an important factor in understanding the how and when reproductive and somatic tissues are segregated and positioned. As cleavage of the asexual gonidium commences, each division is preceded by a period of enlargement and adjustment which helps position the axis of cytokinesis and the alignment of the resulting cells. Previous reports do not fully appreciate the importance of these movements; therefore, their diagrams do not compensate for the cellular aligned, diagrams are not wholly valid. By correctly adjusting and aligning these embryonic cells, it is possible to recognize the third cleavage which results in an 8-cell individual as the division which delineates the animal from the vegetal pole. In all subsequent divisions, new cells are cut off toward the phialopore; therefore, cellular products from animal and vegetal regions do not mix. The integrity of these distinct regions is always maintained. By the 32-cell stage, the 16 pregonidial initials are formed. Future divisions on these 16 cells are unequal, ultimately resulting in 16 gonidia and their somatic derivatives. The final result, after inversion, is a clearly defined organism with reproductive potential located in the posterior of the individual.