Peridiniacese 75 



OCCURRENCE AND DISTRIBUTION. The great majority of the Peridiniacese 

 are constituents of the marine plankton, but there are quite a number 

 of forms in the plankton of rivers arid lakes, and also in the more stagnant 

 waters of bogs and ditches. One form, Glenodinium foliaceum Stein, is 

 apparently restricted to brackish water, and a few others occur both in 

 brackish and fresh water (e.g. Hemidinium nasutum Stein, Gymnodinium 

 teruginosum Stein, Ceratium hirundinella O. F. M., Gonyaulax apiculata (Pen.) 

 Entz and Peridinium Willei Huitf.-Kaas). Although the genera and species 

 of the Peridiniaceae are not numerous in fresh water, certain forms, such as 

 Ceratium hirundinella and species of Peridinium, often occur in prodigious 

 abundance and are sometimes largely the cause of the ' water-bloom ' 

 previously described (p. 32). In the sea, a distinct colouration of the water 

 may be caused by the abundance of Peridinians. In the Indian Ocean vast 

 quantities of Ceratium volans Cleve sometimes give the water a brownish- 

 purple colour; in the Japanese seas Gonyaulax polygramma Stein is 

 frequently the cause of a brown colouration of the water; and in the 

 vicinity of Bombay Peridinium sanguineum Carter has been known to 

 colour the sea red. Gonyaulax polyedra Stein causes a red colouration 

 of large areas of the sea off the coast of California during the summer 

 months; it also exhibits a luminosity at night. In describing the occur- 

 rence of this organism Kofoid states that ' the decay of countless millions 

 of these organisms in the water and upon the beaches where they are 

 continually stranded by the receding waves, creates a nauseous and pene- 

 trating stench of a most disagreeable nature. The products of decay 

 (and metabolism ?) of these organisms are toxic to many marine organisms, 

 which die in great numbers and are cast up by the tide upon the beaches.' 

 The organisms affected are mainly bottom-forms, such as Holothurians, 

 Sipunculids, littoral Crustaceans, and bottom-feeding fish, such as the Sting 

 Ray and the Guitar Fish (Kofoid, 11). 



Kofoid ('10) finds that the more common plankton-species live within 

 100 fathoms of the surface of the ocean, and that below 50 fathoms a large 

 percentage of the individuals show degenerative changes in the chromato- 

 phores and become moribund. 



Some members of the Peridiniaceae, more especially some of the species 

 of Ceratium, are distinctly luminous, and to some extent they contribute to 

 that luminosity of the sea of which the Pyrocystaceae are the principal cause. 



Of the freshwater forms, some attain their maximum vegetative abundance 

 in the warmer months and others in the colder months. Also, certain species 

 which in more northern latitudes are periodic in their assumption of the 

 motile vegetative phase, and therefore periodic constituents of the plankton, 

 are perennial constituents of the plankton of more southern latitudes. Such 

 are Peridinium Willei and Ceratium hirundinella. 



