156 ^ CENTURY OF PROGRESS IN THE NATURAL SCIENCES 



the pigments have been found to consist of chlorophyll a, chlorophyll e, beta carotene, 

 and four xanthophylls, three of which, as far as we know, are peculiar to the Dino- 

 phyceae) ; and (2) the storage of food in the form of starch or oil. 



The cells of members of the Dinophycidae are either naked or are provided, in the 

 forms referred to as armored dinoflagellates, with a cellulose wall, the theca. (The family 

 Amphilothaceae comprises a small number of poorly known marine genera which possess 

 an elaborate internal skeleton that may be silicified.) In some forms the cell is adorned 

 with cellulosic horns (e.g., Ceratium) or saillike processes (e.g., Ornitliocercus) which 

 aid in flotation. In the thecate, flagellated forms, the theca is made up of a series of 

 articulated plates (except in members of the small family Ptychodiscaceae, in which it 

 is homogeneous), the number and arrangement of which are important characters in 

 classification. 



As regards method of nutrition, the Dinophycidae include both photosynthetic and 

 heterotrophic forms (saprophytes, ecto- and endoparasites, and types with holozoic 

 nutrition). 



The genera Polykrikos and Nematodinium possess nematocysts comparable to those 

 occurring in coelenterates. 



The subclass Demosphycidae includes forms which are less specialized than those 

 belonging to the Dinophycidae. The motile stages are biflagellate (with the flagella 

 dissimilar or showing different movements) but do not show a dinoflagellate organiza- 

 tion. In the vegetative condition the cells are provided with a cellulose wall (except 

 in Desmoniastix which is naked) that consists of two valves joined by an antero-posterior 

 suture or that splits into two valves along an antero-posterior plane when the protoplast 

 is caused to swell. The sulcus and girdle are lacking and the two flagella are anterior 

 in position. (The genus Desmocapsa is nonmotile in the vegetative condition and forms 

 small palmelloid aggregates.) The Desmophycidae are placed in the Dinophyceae pri- 

 marily on account of the structure of the nucleus. As far as known, the chromatin 

 threads show the same moniliform condition as is characteristic of the Dinophycidae. 



The usual method of reproduction is by cell division, which in some forms is effected 

 while the cell is motile, in others during an immobile phase. Cysts with a thick wall 

 and abundant stored food are produced in a number of species, especially those inhabit- 

 ing fresh water. The occurrence of sexual reproduction in the pyrrophycophytes has 

 been established with certainty only in two species (Gross, 1934; Diwald, 1938). 



History: ". . . and all the waters that were in the river were turned to blood. 

 And the fish that was in the river died; and the river stank, and the Egyptians 

 could not drink of the water of the river; and there was blood throughout all 

 the land of Egypt." (Exodus, vii. 20, 21.) 



Although the luminescent members of this group and those which, when 

 present in large numbers, give a blood-red color to water have attracted the 

 attention of man for centuries, the freshwater Ceratium hirundineUa and Peri- 

 dinium cinctum are the forms to have been described first in a sufficiently pre- 

 cise manner to be recognized by later workers. They were described by 0. F, 

 Miiller in 1773 as Bursaria hirundinella and Vorticella cincta. These two species 

 and a marine form which Miiller described later were subsequently redescribed 

 and illustrated by him in 1786 in his Animalcula infusoria fluviatilia et marina . . . 



Following the publication of several papers in the proceedings of the Berlin 

 Academy describing new genera and species and other observations upon Dino- 

 phycidae, Ehrenberg in 1838 gave the first treatment of them as a coherent group 

 in his famed work Die Infusionsthiere als vollkommene Organismen. Ehrenberg 

 (1838, p. 249) placed them, along with certain organisms which he erroneously 

 classified with them, in his twelfth family, the Peridinaea or "Kranzthierchen" 

 (wreath animalcules), which formed the last family in his group "Polygastrica 

 anentera," the gutless stomach animalcules. 



