FAMILY PERIDINIACEAE 



11 



SYSTEMATIC DESCRIPTION 



As indicated on page 4 , the following families are 

 included in this paper: Peridiniaceae, Ceratocoryaceae, 

 Gonyaulacaceafe, Goniodomaceae, Ceratiaceae. The ar- 

 rangement of the families does not indicate relation- 

 ships, but rather expresses the degree to which the fam- 

 ilies have been studied; the first ones the most inten- 

 sively. 



Family PERIDINIACEAE 



Diagnosis . "Shape of the cell variable, spherical 

 to longish; small horns often on the hypotheca. Apex 

 present or absent. Girdle circular or somewhat spi- 

 raled; there are right and left spirals. Theca in 'youth' 

 quite thin, later usually developed into stronger theca 

 which falls apart into dissimilarly shaped polygonal 

 plates. Tabulation very different, variable, malforma- 

 tions even common. It is scarcely possible to set up 

 for Peridinium and its relatives, general valid plate 

 patterns; mostly there are 6-7 precingular plates, 5-6 

 postcingular, and 2 antapical plates which only in Dl- 

 plopsalis may be coalesced. The tabulation of the epi- 

 theca is more variable than the hypotheca. Surface of 

 the theca with areolae, papillae, spines, lists, or pores; 

 seldom smooth. Plasma of marine forms sometimes 

 colored. Stigmas in freshwater forms rare and little 

 considered, often pale. In marine forms pusules. 

 Chromatophores often in large numbers. Plasma inclu- 

 sions, starch, fatty substances, pyrenoids, rods (rhab- 

 dosomes). Nucleus roimdish to longish. Colony forma- 

 tion in one case. Formation of cysts after casting of 

 theca. Different icinds of reproduction. Length 18 mi- 

 crons to 300 microns. Fresh-, brackishwater, and ma- 

 rine." (Lindemann, 1928, p. 88.) 



Three genera are established at present. They can 

 be differentiated in the following manner according to 

 Lindemann (1928, p. 88): 



A. Only one of the antapical plates drawn out into a 

 short, hollow horn or spinelike point; shape + spin- 

 dle-shape Heterocapsa 



B. Cell otherwise shaped 



a. Shape at both poles more or less ellipsoidally 

 compressed; at the left margin of the longitudinal 

 furrow (on the hypotheca) is a conspicuous list 

 which can reach over to the antapex; antapical 

 plates two, rarely one Diplopsalis 



b. Otherwise shaped, two antapical plates 



Peridinium 



Remarks . The above description and key clearly in- 

 dicate the insufficiency of our present knowledge. This 

 allows us to make neither a clear-cut definition of the 

 family Peridiniaceae as contrasted with the remaining 

 families, nor to establish generic diagnoses and descrip- 

 tions which will fit into the family description and at the 

 same time be exclusive and distinct. It should be empha- 

 sized that Lindemann (1928) was not at fault. His at- 

 tempt at classifying the Peridineae was remarkably suc- 

 cessful, considering the meager data at his disposal. 

 The only genus of the family treated in this report is 

 Peridinium. 



Genus PERIDINIUM Ehrenberg 

 Diagnosis 

 See Lindemann, 1928, p. 89. 

 Description 



Remarks . Because of our present hazy conception 

 of this genus, a redescription is necessary. The follow- 

 ing description is based solely on the representatives in 

 which the skeletal morphology has been worked out in 

 detail. It is intended to be but tentative and thus to be 

 filled in and rounded out as more material accumulates. 

 It must be stressed, however, that amendment should be 

 made only on the basis of material obtained by the com- 

 plete dissection of specimens and of material subjected 

 to a statistical analysis of form variation. 



Dimensions . Among the forms in this report the 

 total length (1) varied from 44 microns in P. pallidum 

 to 275 microns in P. truncatum; the diameter (d) from 

 35 microns in P. pallidum to 200 microns in P. trunca- 

 tum. Many other forms ascribed to this genus are 

 smaller; e.g., P. faeroense is 16 microns in diameter. 



Shape . All the forms treated in this report, except 

 P. pallidum, possess three well-developed horns, al- 

 though many other species ascribed to the genus are 

 hornless and some even spineless, and, in extreme 

 cases, completely spherical. Whether all these species 

 should be regarded as generically identical cannot be 

 decided at this time. The body is usually longer than 

 wide, but may be spherical, though rarely wider than 

 long. All the forms here treated are much longer than 

 wide, owing primarily to the long horns, the 1/d ratio 

 being as high as 1.5 in P. truncatum . The h/d ratio, 

 which expresses the length of the body exclusive of the 

 antapical horns (h) relative to the diameter, varies 

 from 0.53 in P. claudicanoides to 1.76 in P. depressum 

 var. tenellum . The angle which expresses the amount 

 of anteroposterior compression of the body a varies 

 from 78° in P. depressum to 139" in P. depressum var. 

 convexius . 



Girdle . The girdle is more or less equatorial, 

 sometimes encircling the body in one plane, but usually 

 forming either a descending or an ascending spiral. Al- 

 though it is usually displaced, there is never any over- 

 hang. It seldom encircles the body at right angles to 

 the longitudinal axis, but is deflected from this position; 

 in the forms treated herein, this deflection is from 10° 

 to 15°. The girdle may or may not be excavated. 



Sulcus . The sulcus is a groove on the ventral side 

 of the body extending from the ends of the girdle, or 

 from somewhat anterior to them, to the antapex of the 

 body. In it lies the flagellar pore. The pore is usually 

 oval in shape and the theca of the sulcus is so con- 

 structed that the pore opens laterally instead of directly 

 ventrally. The plate complex of the sulcus may spread 

 out to some extent, forming a wide ventral area with the 

 sulcus proper located within it. 



Plate pattern . If the broad generic concept of 

 Lindemann (1928) is accepted, there are a great number 

 of plate patterns represented in the members of Peri - 

 dinium . This is particularly true of the epitheca. The 



