54 



Peridinieae 



Most of the Gymnodiniacese are marine organisms, although many species 

 of the genus Gymnodinium occur in fresh waters, generally in small pools 

 and ditches containing much vegetation. Spirodinium, Cochlodinium, and 

 others are exclusively marine, but the species of Hemidinium chiefly inhabit 

 fresh water. Herdman ('11) has furnished some interesting observations on 

 the occurrence of Amphidinium operculatum Clap. & Lachm. on the beach 

 at Port Erin in the Isle of Man. It is evidently a shore-form, living on the 

 surface of the sand, and like other Peridinians, sensitive to light. Herdman's 

 observations tend to show that it is either periodic or spasmodic in its 

 appearance, but insufficient is known concerning the physiological require- 

 ments of these organisms to enable any definite statements to be made 

 regarding their sudden appearances and disappearances. 



A member of the Gymnodiniaceas which requires special mention is 



Polykrikos (fig. 39). Originally described 

 by Biitschli (73) as an Infusorian and 

 afterwards referred by Bergh ('81) to the 

 so-called Cilioflagellata, this plankton- 

 organism has recently been carefully 

 examined by Kofoid ('07 A), who has 

 shown that it is merely a member of 

 the Gymnodiniacea' with a permanent 

 colonial organization. There are two, 

 four, or eight transverse groves, each 

 with its flagellum and each corresponding 

 to the equatorial region of a single in- 

 dividual. The longitudinal furrows are 

 all continuous, but there are as many 

 longitudinal flagella as there are trans- 

 verse flagella. The hindmost flagellum is 

 however somewhat longer and acts as the 

 propelling organ. Kofoid also found that 

 the nuclear division was not always 

 coincident with, but often lagged behind 

 the multiplication of superficial structures 

 such as furrows, flagella, etc. Polykrikos 

 is therefore a permanent colonial member 

 of the GymnodiniaceaB consisting of two, 

 four, or eight individuals which are 

 only incompletely separated. Temporary 

 colonies occur in Spirodinium geminatum 

 and in the active Gt/>iinodinium-sta,ges of some of the Peridiniaceae (vide 

 fig. 51 K and L). 



... const. 



-Up. 



flagella, and flagellar pores in a some- 

 what contracted individual. Const., 

 constriction between individuals of 

 colony; /./., longitudinal flagellum; 

 l-f.p., pore of longitudinal flagellum ; 

 n., nuclei ; tr.fi., transverse flagellum ; 



