all kinds, preventing them from settling among the 

 feeding zooids. Usually the little jaws continue to 

 clamp on victims until they die and decompose. Bac- 

 teria and other microorganisms from the decay proc- 

 esses may well augment the diet of the feeding mem- 

 bers of the bryozoan colony. 



Under the microscope the gelatinous matrix of a Pec- 

 tinatella colony is seen to be studded with delicate 

 flower-like individuals, each with a crown of ciliated 

 tentacles that gather food. (Pennsylvania. Ralph 

 Buchsbaum) 



About 6000 different species of living moss ani- 

 mals have been discovered, distinguished primarily 

 upon differences in the chambers they construct. One 

 small class is confined to fresh water. With rare ex- 

 ceptions, all members of the other, larger class live 

 where the sea has its full salinity. Most are shore or 

 shallow-water forms. They occur in all latitudes. Some 

 are known from depths of 19,500 feet. 



Fresh-water Bryozoans 



( Class Phylactolaematd) 



A microscope is needed to see that in this class a 

 little flap of body wall projects over the mouth as 

 though guarding the gullet. Yet this detail has given 

 the name of the class, from the Greek phylacterion, 

 a guard, and laiinos, the gullet. Far more obvious is 

 the fact that the tentacle crown is horseshoe-shaped 

 or at least kidney-shaped, rather than circular. The 

 body wall of each zooid contains a layer of muscles 

 and the body cavity (coelom) is a colonial affair, con- 

 tinuous from one zooid to the next. 



Fresh-water bryozoans are widely distributed, often 

 cosmopolitan. During warm weather they reproduce 

 sexually, but when winter comes they bridge it in the 

 form of asexually produced armored balls of cells 

 called statoblasts. These latter tolerate freezing in the 

 ice, and can be carried from pond to pond on the 

 muddy feet of birds and muskrats. The statoblasts 

 are released in autumn when the parent colony dies 

 and disintegrates. 



On the undersides of stones and sticks in ponds and 

 streams, particularly in shady places, fine-branching, 

 vinelike growths or bushy clumps with a zooid in 

 each end chamber are usually either Fredericella or 

 Phnnatella. The former has oval or kidney-shaped 

 crowns of tentacles, the latter strictly horseshoe- 

 shaped food-capturing organs. 



Another type of moss animal in fresh waters pro- 

 duces masses of gelatinous material as a base. Pec- 

 tinatella individuals form a thin crust over the com- 

 mon jelly secretion, organized into a mosaic of brown- 

 streaked areas each half an inch across, on a mass 

 reaching two feet or more in diameter. The brown 

 streaks radiate from a center, yet each streak is itself 

 a complex colony — a radial line of zooids. Each 

 area in the mosaic may include twelve to eighteen 

 zooids, all reaching out their feeding tentacles, yet 

 able to snap back into the protection of the jelly. 



Pectimitella's central jelly becomes the repository 

 for the innumerable statoblasts. These are armed with 

 a belt of hooks around an encircling air-filled cushion 

 suggesting a life preserver. Empty shells of germi- 

 nated statoblasts and dead ones sometimes drift to 

 shore in windrows, speckling a beach to a width of 

 one to four feet from the water. 



Pectinaiella forms fixed masses on underwater ob- 

 jects. CristaielUi remains oval or elongate, as a creep- 

 ing ruglike colony often encountered on the under- 

 side of a water-lily leaf. These colonies glide very 

 slowly over plant stems, apparently through con- 

 certed movement of the muscles in the body wall; 

 of the zooids that secrete the underlying jelly. Half 

 an inch to an inch a day are respectable speeds for 

 this bryozoan. At intervals a colony of Chstatella 



152] 



