through the shell of an animal that has withdrawn on 

 being lifted out of the sea in a tow net. When un- 

 disturbed it spreads its pseudopodial network in sur- 

 face waters and feeds on diatoms and algae, other 

 protozoans, and occasionally even larger animals. 

 Elphidhiin crispa is another pelagic form, and is a 

 giant among modern species. Its flattened, spiral, 

 sculptured, many-chambered shell reaches a diam- 

 eter of ^s of an inch and superficially resembles a 

 small snail shell, so that originally it was classed as a 

 moUusk. Leeuwenhoek first found this genus in the 

 stomach of a shrimp, but Elphidium can ingest, along 

 with its unicellular plant diet, the small copepods 

 that are relatives to the shrimp. 



Many forams harbor green or yellow bodies be- 

 lieved to be modified flagellates. Reproduction in 

 forams takes place by multiple division and involves 

 an alternation of asexual and sexual forms. In the 

 typical many-chambered species the forms that re- 

 produce asexually have shells of small size, those that 

 reproduce sexually have larger shells. The sex cells 

 are usually flagellated but sometimes are ameboid. 

 The life cycles of forams are marvelously complex, 

 but details must be sought in advanced treatises. 



THE HELIOZOANS 



The "sun animalcules" or heliozoans, found mostly 

 in fresh waters, are spherical ameboid protozoans 

 with stiff radiating pseudopods that serve only for 

 feeding, not for moving about. The pseudopods are 

 supported by stiff internal protoplasmic rods and 

 covered with thin, clear, streaming surface proto- 

 plasm. In many species the body has a gelatinous 

 covering in which foreign particles or secreted plates 

 or needles of silica are imbedded. Or it may be en- 

 closed, as in the common but lovely Clathndina. in 

 a spherical latticed cage. Clathndina is fastened by a 

 stalk to the substrate, and the pseudopods protrude 

 through the lattice openings. The more typical free- 

 floating forms are motionless or move only very 

 slowly. Passing organisms that happen to touch the 

 outstretched stiff pseudopods adhere to them and are 

 quickly paralyzed, as if by a toxin. The pseudopods 

 may shorten and carry the prey to the main body 

 mass, or several may surround the victim first and 

 then slowly withdraw into the main body. The two 

 most familiar heliozoans of pond water are both 

 free-floating. The small Actinophrys sol has one nu- 

 cleus and a body that is not clearly divided into two 

 regions. The much larger Actinosphaeriiun ekh- 

 horni. visible to the naked eye, has a distinct outer 

 layer surrounding a granular interior in which one 

 can usually see recently eaten diatoms or other algae, 

 and small protozoans or crustaceans. A number of 

 small heliozoans may unite temporarily when they 

 capture and ingest large prey. Asexual reproduction 

 is by fission or budding. 



THE RADIOLARIANS 



The radiolarians are all marine and pelagic ame- 

 boid protozoans, abundant especially in warm seas. 

 They nearly always have siliceous skeletons, many 

 of these so exquisitely shaped that Haeckel, the great 

 German biologist and student of the radiolarians, 

 once called them the miniature jewelry of the abyss. 

 Mostly spherical, they extend long, fine, usually 

 stiff raylike pseudopods from which they take their 

 name. The pseudopods are sticky and capture dia- 

 toms, protozoans, and copepods that adhere to them. 

 Radiolarians are of large size as protozoans go. The 

 giant Tlialassicola niicleala is about ' -, of an inch in 

 diameter, and its closely related colonial relatives 

 reach 1 inch or more in length. Tlialassicola has no 

 skeleton, but in most radiolarians siliceous needles 

 are fused into a beautifully symmetrical latticework. 

 The lattice is most often spherical, and in some spe- 

 cies there are a number of concentric latticed spheres, 

 one within the other, like the balls made to show off 

 the skills of Chinese ivory carvers. There is also a 

 bewildering variety of helmet-shaped, disk-shaped, 

 and bell-shaped lattices — all combined in every pos- 

 sible way with beautiful and bizarre ornamentations 

 of spines, hooks, branching thorns, and long, grace- 

 fully curved extensions. The almost endless differ- 

 ences in radiolarian skeletons, each produced in a 

 consistent inherited pattern by what appears to be a 

 relatively formless blob of protoplasm, makes one 

 wonder if this protoplasm is as unorganized and as 

 similar in the various species as its appearance in the 

 naked amebas might lead us to believe. 



A great variety of shell shapes can be seen in many 

 samples of foraminiferan material. ( Otto Croy ) 



