5^. THE INVERTEBRATA 



Order CHLOROMONADINA 



Phytomastigina which have numerous green chromatophores or are 

 colourless ; with reserves of oil ; gullet ; and complex contractile vacuole ; 

 without transverse groove ; possessing a delicate pellicle, or amoeboid. 



Vacuolaria. Typical, bright green members of the group, which 

 pass much of the life history in the palmella stage. In fresh waters. 



Order DINOFLAGELLATA 



Phytomastigina which have numerous yellow, brown, or green 

 chromatophores or are colourless; with reserves of starch or oil or 

 both; with complex vacuole system; with two flagella, one directed 

 backwards and usually in a longitudinal groove (sulcus) and the other 

 transverse, usually in a more or less spiral groove (annulus) ; usually 

 with an armour of cellulose plates, but sometimes amoeboid. 



The complex vacuoles of dinoflagellates are not, as was held, con- 

 tractile, but contain water driven into them through their external 

 pores by the action of the flagella. Their function is unknown. 

 Possibly they are hydrostatic, or alimentary, or both. 



The plane of fission is oblique, but resembles the longitudinal 

 fission of other Mastigophora in passing between the two flagella. 

 Fission may be within or without a cyst: in either case it may be 

 simply binary or repeated ; within a cyst it is sometimes multiple. The 

 products of repeated binary fission of pelagic forms sometimes hang 

 together for a considerable time as a chain. The occurrence oisyngamy 

 is suspected but has not yet been proved beyond doubt. 



The typical members of this order are free-living and highly 

 organized, but it includes forms which are greatly degenerate and 

 only recognizable as belonging to it while they are spores. The 

 members may be holophytic, saprophytic, or holozoic, feeding in 

 the latter case by pseudopodia either from a spot on the sulcus or at 

 any point. They are usually pelagic, sometimes parasitic, and for the 

 most part marine. 



Ceratium (Fig. 40 A). Typical, armoured, holophytic species; with 

 three long spines. In freshwater forms the chromatophores are green ; 

 in marine species they are yellow or brown. 



Dinophysinae. Pelagic genera, often of bizarre form, with the 

 annulus at one end of the body, and the shell in two lateral plates. 



Polykrikos (Fig. 40 B). Soft-bodied species; colourless and holo- 

 zoic; with the flagella and other external features repeated several 

 times along the axis of the body, and the nucleus also repeated, 

 but not in correspondence with the other features (see p. 10). The 

 protoplasm contains peculiar nematocyst-like organs. Holozoic. 



