Luminescent dinoflagellate. Noclihica scintUlans, is 

 noted for tinting the sea surface pink in the daytime, 

 lighting it at night. (England. D. P. Wilson) ' 



the world. On the California coast several epidemics 

 of shellfish poisoning in men have been attributed to 

 the eating of a common California mussel, Mytihis 

 calif oniiamis, which may in summer become loaded 

 with Gonyaulax catenella, known to produce a very 

 toxic substance. 



The most significant of all dinoflagellates are the 

 typical genera Peridinium and Ceralium, of both 

 fresh and salt water, which have large numbers of 

 species and of individuals. Ceratium has three spines 

 on its enclosing armor, and these tend to be short and 

 thick in cold, highly saline waters and very thin and 

 long in warm, less salty waters. The greater surface 

 of the longer, thinner spines retards sinking in the 

 less dense low-salinity warmer water, so that it is 

 actually easier, in certain oceanographic studies, to 

 use the species of Ceratium as a "biological indi- 

 cator" of salinity than it is to make actual measure- 

 ments of salt content. 



Noctilucu is one of the largest, most aberrant, and 

 most conspicuous of the flagellates. What is usually 

 considered a single species, preferably called Nocti- 

 lucu scintillans ("night light that scintillates"), oc- 

 curs off oceanic shores all over the world. The pin- 



head-sized, nearly spherical, and mostly gelatinous 

 bodies are colorless, pale pink, or yellowish, and 

 when dense can make extensive areas of the sea ap- 

 pear, in the daytime, like pak tomato soup. At night 

 this protozoan is a major cause of the luminescence 

 of seas. As ships plow through the water, disturbing 

 billions of NoctHuca, the waves that they set up 

 flame in the darkness, and the trailing wake scin- 

 tillates with minute flashes. Where A'ccr/Ywra-laden 

 waters are thrown with great force against steep 

 rocky shores, the nighttime displays are truly spec- 

 tacular, suggesting fireworks set off under water, 

 though this bioluminescence, or animal light, gives 

 off no measurable heat and dissipates little of the 

 animal's energy. In marine waters that enter plumb- 

 ing installations, the luminescent effects can be start- 

 ling. Inshore winds may compact Noctiluca to a sur- 

 face crust on the waters and also bring them ashore, 

 where they are seen, on sand beaches, as a red scum 

 at high tide mark. A noctiluca was once described 

 by T. H. Huxley as looking like a little peach, with a 

 waving, finger-like tentacle as long as the body, 

 emerging from the place where the stalk of a peach 

 might be. Under the microscope we see that the curl- 

 ing tentacle emerges from one end of a pouchlike 

 depression. The animal floats mostly with the feed- 

 ing pouch down, and the tentacle wafts diatoms and 

 dinoflagellates toward the mouth, or even manages 

 to cram in the larvae of copepods or other crusta- 

 ceans, which distort the enclosing Noctiluca body. 

 Digestion goes on in the protoplasmic mass that lies 

 at the bottom of the pouch, and that branches and 

 rebranches into fine filaments radiating out through 

 the thin gelatinous bulk that adds to the buoyancy of 

 the animal. Organisms too small to be easily strained 

 out of the water by larger animals are thus converted 

 into packages of Noctiluca size. These are then avail- 

 able to small crustaceans, which form the next links 

 in the chains of animals of increasing size that make 

 up the network of animal feeders of the seas. 



THE EUGLENOID FLAGELLATES 

 Distance lends no enchantment to Eiiglena in the 

 mass, and to many people a green pond scum of this 

 flagellate is not pleasing. But close up, under the 

 magnifying powers of a microscope, a single eu- 

 glena, propelled gracefully across a lighted micro- 

 scope field, rich green in color and often beautifully 

 sculptured with surface ornamentation, is as lovely a 

 sight as any living organism. In the various species of 

 Euglena the pellicle may be striated, or ridged with 

 rows of spines or knobs, often spirally arranged; and 

 it is highly elastic, permitting the wormlike creeping 

 "euglenoid" movements named for this common ge- 

 nus. In euglenoids of other genera the pellicle may 

 be rigid. At the front end of a spindle-shaped eu- 

 glena is a flasklike depression, the gullet, and from 



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