Phylum Phaeophyta [ 67 



Family 8. Phyllosiphonacea [Phyllosiphonaceae] Wille in Engler and Prantl. Nat. 

 Pflanzenfam. I Teil, Abt. 2: 125 (1890). Family Vaucheriaceae (Nageli) Areschoug 

 (1850), preoccupied by order Vaucheriaceae Nageli. Family Botrydiaceae Luther 

 (1899). Heterokonta whose bodies are highly multinucleate single cells, filamentous 

 or anchored by filamentous rhizoids. Botrydium is found on damp soil as dark green 

 globes, sometimes as much as 2 mm. in diameter, anchored by much-branched color- 

 less rhizoids. Vaucheria is a familiar alga on damp earth or in fresh water. It consists 

 of irregularly branching filaments, green where exposed to light, colorless where 

 growing downward and serving as rhizoids. The reproductive cells are cut off by 

 walls. The end of an aerial filament, cut off in this fashion, may as a whole act as a 

 spore. In water, the protoplast of such a cell may escape as an exceptionally large 

 zoospore with as many pairs of flagella as the nuclei within it. Antheridia are brief 

 branches, each releasing many minute sperms each with two unequal flagella. 

 Oogonia are globular cells, multinucleate during development, but containing only 

 one functional nucleus when mature. Phyllosiphon is of much the same structure as 

 Vaucheria, but is parasitic in seed plants, particularly Araceae. It reproduces, ap- 

 parently, only by the breaking up of the protoplast to produce minute non-flagellate 

 spores. 



Order 4. ChoanoflageUata [Choano-Flagellata] Kent Man. Inf. 1: 36 (1880). 

 Order Bicoecidea Grasse and Deflandre in Grasse Traite Zool. 1, fasc. 1: 599 

 (1952). 



Non-pigmented flagellates, usually attached, each cell bearing a single flagellum 

 of the type called pantacroneme, with lateral appendages and a terminal whip-lash; 

 the cell bearing also a protoplasmic collar, usually surrounding the base of the flagel- 

 lum. The collar is a means of nutrition. Bacteria and other scraps of organic matter, 

 driven against it by the beating of the flagellum, adhere and are carried to the interior 

 of the cell by flow of the cytoplasm of which it consists. 



It is probable that the pantacroneme flagellum is a variant of the pantoneme 

 flagellum, and that this order belongs naturally in class Heterokonta. It may have 

 evolved from Silicoflagellata; or it may be that the collar is a modified flagellum, 

 and that the group evolved from order Ochromonadalea. 



Most authors have recognized more than one family of choanoflagellates, but 

 genera are not very numerous and one family seems sufficient to accommodate them. 



Family Bicoekida Stein Org. Inf. 3, I Halfte: x (1878). Family Craspedornona- 

 dina Stein 1. c. Families Bikoecidae, Codonosigidae, Salpingoecidac, and Phalansteri- 

 idae Kent op. cit. Families Codonoecina and Bikoecina Biitschli in Bronn Kl. u. Ord. 

 Thierreichs 1: 814, 815 (1884). Families Bicoecaceae, Craspedoynonadaceae, and 

 Phalanasteriaceae Senn in Engler and Prantl Nat. Pflanzenfam. I Teil, Abt. la: 121, 

 123, 129 (1900). Family Gymnocraspedidae Grasse Traite Zool. 1, fasc. 1: 590 

 (1952). Characters of the order. Cells naked, solitary: Monosiga; colonial: Codo- 

 siga James-Clark [Codonosiga Stein), Sphaeroeca. Cells imbedded in gelatinous 

 matter, the collars contracted: Phalanseterium. Loricate: Salpingoeca, Bicosoeca, 

 Poteriodendron. 



The choanoflagellates were discovered by James-Clark (1866, 1868), who made at 

 the same time the discovery that certain internal cavities of sponges are lined by 

 minute cells (choanocytes) of the same structure as the choanoflagellates. From 

 these observations he drew the conclusion that sponges are a sort of flagellates dis- 

 tinguished by the production of exceptionally large and elaborate colonies. Kent 



