ing attached colony, and if abundant in water reser- 

 voirs, imparts a fishy odor to the water, like that of 

 cod-liver oil. Also colonial is Syiiura, with the indi- 

 viduals attached at their inner ends and the flagellar 

 ends extending out radially in all directions. Synura 

 may be very numerous under the ice of ponds in 

 winter. When it is the dominant form in a pond, 

 the water has an odor like that of ripe cucumbers or 

 muskmelon and tastes both bitter and spicy. The 

 odors and tastes imparted by flagellates are due to 

 aromatic oils stored as food reserves and liberated 

 when the animals die. One part of oil from Synura 

 can be detected in twenty-five million parts of water, 

 so that it may be necessary to filter the water or to 

 add to it minute quantities of copper sulphate which 

 inhibits the growth of the small organisms without 

 doing readily detectable harm to man or other ani- 

 mals. Marine chrysomonads often are enclosed in 

 beautiful latticed cases or have the body surface cov- 

 ered or embedded with secreted plates of calcium 

 carbonate called coccoliths. These range from flat 

 oval disks to plates ornamented with long rodlike 

 or trumpetlike extensions. The coccoliths of bottom 

 deposits from tropical and subtropical seas were 

 well known to biologists long before the living flagel- 

 lates that produced the skeletons had ever been seen. 

 The disintegrated skeletons continue to be deposited 

 at a rate that is estimated for an area in the North 

 Atlantic, at a depth of 7200 feet, to be sixty billions 

 of shells per square meter (about ten square feet) 

 annually. They add their bulk to the more numer- 

 ous and more durable shells of ameboid protozoans 

 (forams and radiolarians). 



THE CRYPTOMONADS 



Cryptomonas, of fresh water, is a photosynthetic 

 cryptomonad with two flagella protruding from a dis- 

 tinct opening at the front, and two yellowish or 

 brownish green pigment bodies. The very similar but 

 colorless and saprozoic Chilonionas is the common- 

 est and most familiar cryptomonad of stagnant fresh 

 waters. We know a great deal about its remarkable 

 nutrition. It can synthesize protoplasm from inor- 

 ganic material provided that certain chemicals are 

 present. 



THE DINOFLAGELLATES 



The numerous dinoflagellates are distinguished by 

 the two flagella seen in all the typical forms. In 

 these a long flagellum trails downward with the long 

 axis of the body from a hole in a longitudinal 

 groove, and another flagellum undulates in steady 

 waves in a groove that encircles the body at right 

 angles to the upright axis. They swim in a bouncy 

 sort of way, and occur in incalculable numbers, pro- 

 viding the nutritional basis for the surface-floating 

 animal populations in all seas and in ponds and 



lakes. Some cause the destructive "red tides" re- 

 ferred to below. Most of them are photosynthetic, 

 usually have an eyespot, and have green, yellow, or 

 brown pigment bodies. The single nucleus is very 

 large. Some dinoflagellates live as floating rounded 

 forms that look like algae. Many are believed to be 

 the yellow alga-like bodies seen inside marine proto- 

 zoans, especially in tropical radiolarians. Others are 

 external or internal parasites. The colorless forms 

 engulf small organisms in ameboid fashion. 



Marine dinoflagellates, Ceratium tripos, with three 

 long spines on the encasing armor, are tremendously 

 abundant in surface waters. One extrudes a long fla- 

 gellum. (England. D. P. Wilson) 



The typical dinoflagellates, all with two grooves 

 and two flagella, may be either armored or unar- 

 mored, the latter kind either naked or enclosed in a 

 ceflulose membrane. Most are marine, but some 

 genera are also numerous in fresh waters. Gymnodi- 

 nhiin hrevis. a marine species, suddenly "bloomed" 

 in 1947 in concentrations higher than five million to 

 a quart, causing a "red tide" off the Florida coast. 

 The toxin provided by such large numbers of dino- 

 flagellates killed coastal marine animals over a wide 

 area, and littered the beaches for many miles with a 

 hundred pounds of rotting fish per running foot. Off 

 the southern and Lower California coast destructive 

 red tides are caused in certain summers by the rise 

 of Gcmyaiilax polyliedra, a heavily armored dino- 

 flagellate whose toxin kills fishes, shrimps, crabs, 

 barnacles, oysters, and clams. Similar dinoflagellate- 

 caused red tides also occur off the Atlantic coast of 

 Spain and Portugal, and either red or yellow tides 

 cause serious local problems in many other parts of 



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