Plancton 299 



{c) Tapering filaments that are immersed in more 

 or less spherical masses of gelatine, their points 

 radiating outward; Gloiotrichia, Riviilaria (see 

 fig. 51, on p. 133, and 52), etc. 

 2. Non-filamentous forms having : 



(a) Cells immersed in a mass of gelatine, Micro- 

 cystis (including Polycystis and Clathrocystis, 

 see fig. 51 on p. 133), Coelosphaerium, Chrooco- 

 ccus, etc, 

 h) Cells arranged in a thin flat plate. Tetra- 

 pedia {fig. 51), Merismop^dia (see fig. 53 on p. 

 135), etc. 

 Representatives of all these groups, except the one 

 last named, become at times excessively abundant in 

 lakes and ponds, and many of them appear on the 

 surface as ' Vater bloom." 



Of the green algas there are a few not very common 

 but very striking forms of rather large size found in the 

 plancton. Such are Pediastrum (see fig. 44 on p. 123) 

 and the desmid, Staurastum. There are many minute 

 green algas of the utmost diversity in form and arrange- 

 ment of cells. Most of those that are shown in figure 

 50 on page 129 occur in the plancton; Botyrococcus is 

 the most conspicuous of these. A few filamentous 

 green forms such as Conferva (see fig. 45 on p. 124) and 

 the Conjugates (fig. 41 on p. 119), occur there adventi- 

 tiously, their centers of development being on shores. 



The animals of the plancton are mainly protozoans, 

 rotifers and crustaceans. The protozoans of the open 



Fig. 181. 



I, Philodina. 2, 3, Rotifer. 4, Adineta. 5, Floscvilaria. 6, Stephanoceros. 7,Apsilus. 

 8, Melicerta. 9, Conochilus. 10, Ramate jaws. 11, Malleo-ramate jaws. 12, Micro- 

 codon. 13, Asplanchna. 14, 15, Synchceta. 16, Triarthra. 17, Hydatina. 18, Poly- 

 arthra. 19, Diglena. 20, D^urella, 21, Rattulus. 22, Dinocharis. 23, 24, Salpina. 

 25, Euchlanis. 26, Monostyla. 27, Colurus. 28, 29, Pterodina. 30. [Erachionus. 

 31, Malleate jaws. 32, Noteus. a, 34, Notholca. 35, 36, Anuraea. 37, Ploesoma. 

 38, Gastropus. 39. Forcipate jaws. 40, Anapus. 42, Pedalion. 



From Genera of Plancton Organisms of the Cayuga Lake Basin, by 

 O. A. Johannsen and the junior author. 



