STUDIES IN THE MORPHOLOGY, TAXONOMY, AND ECOLOGY OF THE PERIDINIALES 



forms it is necessary to bear In mind that the ventral 

 view should be at right angles to the longitudinal axis, 

 which axis is defined as the line running through the ap- 

 ical horn and bisecting the hypotheca midway between 

 the bases of the antapical horns. It must be remembered 

 that when a specimen comes to rest at the bottom of a 

 drop of mounting fluid it does not present this view. 

 When a specimen of Peridlnium depressum comes to 

 rest with ventral side uppermost, it presents an antero- 

 ventral aspect, resting on the dorsal side of the girdle 

 and on the two antapical horns. This position should 

 not be used as the standard in measuring, since consid- 

 erable variation in the optical projection of the body is 

 caused by slight differences in the length or divergence 

 of the antapical horns on which the organism rests. It 

 is necessary to mount in glycerin jelly or similar me- 

 dium in order to orient the specimen in the proper man- 

 ner and arrange it in a proper position. 



As defined in this work, the ventral view is the one 

 in which the sulcus lies midway between the lateral 

 sides of the body and in which the dorsal part of the gir- 

 dle can be superimposed on the anterior end of the sul- 

 cus when the microscope is focused downward. 



Because of the very great differences in the shapes 

 of the various genera of the Peridlniales, it is not always 

 possible or desirable to make the same measurements 



on all forms. There are particular dimensions which 

 are significant in each genus. A description of these 

 measurements and the method of making them will be 

 given in the introduction to each genus. 



The question of nomenclature always arises in the 

 treatment of this group of organisms. The group has 

 been studied by both botanists and zoologists, each using 

 the nomenclature of his particular school. It seems 

 futile to discuss the question whether the members of 

 this group are plants or animals. They cannot be placed 

 unreservedly in either the plant or the animal kingdom. 

 We can only discuss their relative similarities to each 

 of these kingdoms. Since one is forced to adopt either 

 plant or animal nomenclature, It is only reasonable that 

 the nomenclature should fit the views of the author. This 

 author believes that the plant char acteristicsof the peri- 

 dinlans outweigh the animal. Hence, botanical nomen- 

 clature is used in this report. Many of the peridlnians 

 are photosynthetic and practically all show some signs 

 of a ceUulose-like substance in their body wall (All- 

 mann, 1855; Klebs, 1883; Schutt, 1895; Mangin, 1907, 

 1908). The discovery of two filamentous algae with 

 Gymnodlnium spores by Pascher (1914) supports the 

 interpretation of these forms as plants, but the discov- 

 ery of an amoeba with similar spores (Pascher, 1915) 

 tends to outweigh this discovery. 



SURVEY OF THE ORDER PERIDINIALES 



General Statements 



The Peridlneae, or Dinoflagellata, are subdivided 

 into two main groups: the Adinlferae and the Dintferae, 

 the former without, the latter with a girdle, i.e., a body- 

 encircling transverse groove in which the transverse 

 flagellum is lodged. Diniferae are divided into seven 

 orders, one of which is the Peridlniales, to which the 

 material of this thesis belongs. 



The Peridlniales may be characterized briefly by 

 the following features: The body is surrounded byathe- 

 ca, which is made up of definite polygonal plates (ex- 

 cept in prevalvate stages of Glenodiniaceae) of unequal 

 sizes and not arranged in a bilaterally symmetrical 

 manner. These features, especially the last one, sepa- 

 rate the Peridlniales from the Dinophysiales, which is 

 the remaining large order with thecate and plated body, 

 and in which the theca is divided longitudinally into right 

 and left valves. 



The most recent synopsis of the Peridineae which 

 includes the Peridlniales is that of Lindemann (1928) in 

 Engler and Prantl's Pflanzenfamilien. Kofoid, who 

 worked extensively on the Peridineae, never treated this 

 order as a whole. Schiller's synopsis of the Dinoflagel- 

 lata (1931 to 1933) sUll lacks the part on the Peridlni- 

 ales. 



Families 



Lindemann (1928) divided the order into fourteen 

 families. Instead of giving abbreviated diagnoses of 

 these, a condensation of Lindemann's key for distin- 

 guishing these families is given below in order to offer 

 a brief survey of the order. 



Key to the Families of the Peridlniales 

 (Lindemann, 1928, p. 79) 



A. Shell tough- skinned; composed of unequally sized, in- 

 distinct, major polygons, not visible in young stages 

 Glenodiniaceae 



A. Shell consists of more or less heavy armor composed 

 of dissimilar polygonal plates which are evident in 

 yoimg stages B 



B. Girdle Indistinctly developed as a narrow band . . 

 Podolampaceae 



B. Cell with very distinct girdle C 



C. Cell in apical view quite or nearly circtilar; epitheca 

 distinctly smaller than hypotheca, flat, lid-shaped. 

 Either there are spinelike processes with a central 

 axis which extend in different directions (each about 

 as long as the body), or the antapical pole carries 2 to 

 3 strong spines D 



C. Cell of other shapes; there are frequently processes 

 or spines but these are never so long as the body nor 

 with a central axis E 



D. Processes or spines only on the hypotheca .... 

 Ceratocoryaceae 



D. Both epitheca and hypotheca carry long processes . 

 Cladopyxlaceae 



E. Girdle equatorial or anterior; only one plate at the 

 antapex, which terminates in a horn or spine . . . 

 Oxytoxaceae 



E. Commonly at least two antapicals, or one antapical 

 and one posterior intercalary; rarely one antapical, 

 in which case there is no end spine or point . . F 



F. Cell strongly flattened anteroposterlorly; antapicals 

 none or more than two G 



F. Cell otherwise shaped H 



G. AnUpical plates absent (?); longitudinal axis oblique 



