MESOZOIC AND CAINOZOIC DINOFLAGELLATE CYSTS 



13 



(4) The Morphology of Cysts. 



(a) Major Cyst Types. 



The cysts are always smaller than the motile cell and can be grouped according to 

 their degree of contraction. The degree of contraction also affects their general 

 appearance, for those which are most condensed bear little superficial resemblance 

 to the parent cell, whereas those that are near the motile cyst in size closely resemble 

 it in appearance. Consequently two groups of cysts are here recognized, the chorate 

 (or condensed) cysts and the proximate cysts. 



In both these groups of cysts, the two wall layers are generally in close contact and 

 only rarely come apart, but there is a third group, here called the cavate cysts, in 

 which a space, or spaces of notable size, occurs between the periphragm and endo- 

 phragm. This space is here named the pericoel ; it separates an inner body (cap- 

 sule) formed by the endophragm from the outer cyst wall, the cavity of this inner 

 body is called the endocoel. 



(b) Cyst Openings. 



The polygonal openings found on cysts have been called pylomes by Eisenack. 

 This is, however, a broad term and includes also circular or slit-like openings which 

 are in no way characteristic of, or confined to, the dinoflagellates. Evitt's term 

 archaeopyle refers specifically to those kinds of pylome which characterize some 

 dinoflagellate cysts. They are usually polygonal and precisely located and orientated 

 on the test, corresponding to specific locations in the structure of the tabulate dino- 

 flagellates. The terminology used here generally corresponds to that proposed by 

 Evitt (1961, text-figs. 5-8), with the addition of epitractal, for archaeopyles formed 

 by breakage parallel, and immediately anterior to, the cingulum (equivalent to 

 epithecal archaeopyles of Norris 1965), and cingular, for archaeopyles formed by 



A A 



11 



Y7 



conical subconical tapering cylindrical infundibular flared tubiform buccinate 



lagenate bulbose 



annular 



complex 



soleate 

 c mplex 



J> 



r f 



arcuate 

 complex 



LjUJWl-iHv 

 •I }■ 



■ifMnit' 



linear simulate 



complex complex 



o 



CD' 



erect curved sinuous 



latispinous 



cross sections 



slender 



□ 



Fig. 3. Illustrations of the terms used to describe the overall shape of the 

 processes and process complexes. The distal end is uppermost in each case. 



