MORPHOLOGY AND TAXONOMY OF MASTIGOPHORA 275 



etc.) have attaching trunks or peduncles recalHng the epimerites 

 of gregarines; others are sessile, while still others are unattached 

 coelozoic parasites of body cavity or gut. A curious Cestode-like 

 form, found in the intestines of maldanid annelids, was discovered 

 by Dogiel (1907) and described as a Mesozoon under the name of 

 Haj^Iozcon (Fig. 133). Chatton (1920), however, has shown that 

 its affinities are with the Blastodinidte and particularly with Blasto- 

 dinium. 



The Dinoflagellida are distributed amongst three sub-orders— 

 Diniferina, Adinina and Cystoflagellina. 



Sub-order 1. Diniferina, Bergh. 



The majorit\' of forms with characteristic dinoflagellate struc- 

 tures are placed here. One or more transverse furrows bearing 

 flagella are typically present, and the longitudinal flagellum is 

 usually directed backward. Three Tribes are recognized: (1) 

 Gymnodinioida^; (2) Perididinioidae, and (3) Amphilothioidse. 



Tribe A. Gymnodinioid^, Bergh, Em. Poche.— As the name 

 indicates these interesting forms are either naked or provided with 

 delicate cellulose coverings which are not laid down in plate form. 

 In respect to furrows, flagella, and general structure the}' conform, 

 even when naked, to other members of the su})-order. They are 

 usually somewhat dorso-ventrally flattened and provided with 

 many small discoidal green or yellow chromatophores although 

 some species are colorless. Stigmata are occasionally present, 

 located in or near the longitudinal furrow. Nutrition is either 

 autotrophic or heterotrophic (saprozoic, holozoic, or parasitic) and 

 reproduction usually takes place during enc;\'stment, rarely in the 

 motile stages. 



In Hemidinium, Stein, the cross furrow does not run entirely 

 around the cell, but, with the flagellum, stops in the center of the 

 dorsal surface. Gymnodininm is frequently colorless, taking in solid 

 food and, in some species {Gymnodinium zachariasi, Lemmermann), 

 forming branched pseudopodia. Other species {Gymnodinium para- 

 siticinn, Gymnodiniinn rosewn) are parasitic on the eggs of copepods. 

 Other genera are peculiar in having onh' a short free-swimming 

 period after which they pass into an alga-hke resting phase. Such 

 forms as Cystodinimn and Gymjiodininm hnnda are strikingly 

 suggestive of the Phytodinidse in ha^•ing motile stages lasting 

 from only a few minutes to an hour or so, while in Ilyjinodinium 

 no motile stage whatsoever is known. It is in the life history of 

 these types that the so-called "horned cysts" are found (see p. 271). 

 The genus Gknndinivm difl'ers from most of the Gymnodinidfe in 

 having a definite but delicate and non-articulated .shell (Fig. 131, J). 



