The Mastigophora 139 



(Fig. 4. 17, E). The epicone and hypocone, the anterior and posterior 

 regions of the body, are marked off by the girdle. The sulcus (longi- 

 tudinal furrow) is usually a straight groove intersecting the girdle, al- 

 though it may undergo spiral torsion (Fig. 4. 17, B), or may be expanded 

 into a "ventral area." From the sulcus arise the tentacle of Protodinifer 

 (Fig. 4. 17, E) and the prod of Erythropsis (Fig. 4. 17, G). The two 

 flagella of typical species also emerge through one or two flagellar pores 

 in the sulcus (Fig. 4. 17, A). The transverse flagellum is often ribbon- 

 like (81, 159). Occasionally, as in Peridinium, species within a genus 

 may differ in this respect (81). 



A theca, composed of a cellulose-like substance and sometimes im- 

 pregnated with calcium salts, is present in many dinoflagellates. The 

 typical theca is composed of plates, the margins of which may be sepa- 

 rated by intercalary bands (Fig. 4. 17, C) in some species and particularly 

 in older specimens. The theca covering the epicone is known as the 

 epitheca; the posterior portion, as the hypotheca. The two are joined 

 by the girdle hand, composed of one or more girdle plates. The theca 

 may, as in Ceratium hirundinella (Fig. 4. 17, F), contain pores through 

 which extend cytoplasmic papillae. 



There are commonly two vacuoles, or pusules (Fig. 4. 17, A), usually 

 containing a pink fluid. A slender c^jial extends directly from each 

 pusule to a flagellar pore or else joins a common canal which opens 

 externally. Intake of fluid has been observed in pusules of Peridinium 

 steini (155), and it has been suggested that a pusule may function as a 

 pharynx for intake of liquids and possibly solid particles (159). 



The nucleus usually contains one or more nucleoli and many long 

 chromosomes whose beaded structure may persist through mitosis. 

 Chromatophores, present in many species, are often golden-brown to 

 dark-brown, although sometimes yellow, orange, green, or bluish-green. 

 In addition, various cytoplasmic pigments — either diffuse or forming 

 granules or globules — occur in many species (159). The known pigments 

 include chlorophyll a, chlorophyll r, peridinin, /^-carotene, dinoxanthin, 

 diadinoxanthin, and neodinoxanthin (Chapter I). Stored reserves in- 

 clude starch and lipids. A simple stigma, composed of red granules, 

 occurs in various fresh-water species. At the other extreme, the Pou- 

 chetiidae possess a complex ocellus (Fig. 1. 17, H, M) composed of a 

 lens and a mass of pigment. 



The group shows a strong trend toward holozoic feeding, as indicated 

 by inclusions which are obviously ingested food in many species and 

 apparently such in others. In the chlorophyll-free Cochliodinium rosa- 

 ceum (159), Oxyrrhis marina (Fig. 4. 18, C), Noctiluca milaris, and 

 others, holozoic nutrition is undoubtedly important. Ingested food also 

 appears in various chlorophyll-bearing species of Gymnodinium, Gyro- 

 dinium, and Amphidinium (159). Furthermore, such thecate types as 



