Rotlferae 



They are classified as plankton forms and as bottom forms. The former are more 

 IjQiortant and are used by the small and smallest fishes. In the eutrophic ponds of 

 Sachsenhausen, Pauly distinguished groups which occurred predominantly in plankton only 

 during one or several periods ( Conochilus. Brachionua . Anurea ); also the regular but sparing 

 ( Asplanchua. Synchaeta ); and singly and irregularly occurring forma ( Triarthra . Polyarthra. 

 Rattulua and many others). The rotifers ( Brachionua . Anurea and others) are likewise found 

 regularly in the trout ponds. 



Cruataceae 



The higher (about 1 cm. length) crustaceae, ring crabs ( Arthrestaca) . flea crabs 

 ( Oammarus pulex . Carlnogammarus ) and water asellus ( Asellus aouatlcus) are found almost 

 always in ponds, and the former particularly in trout ponds and in strong-current locations, 

 the latter on plants and in mudc^ or slightly unclean places. Of the small, mostly 1 to 5 

 mm. sized vegetation and bottom forms, the lentil crab ( Eurycercua lampllatus) . the water 

 flea ( Sida cristalllna ) and various Cyclops species are particularly frequent. 



Also found, but not exactly in large quantities are Ostraooda. Alopa species, Simo- 

 cephalua and Daphne magna . Ttiej prefer small, fresh3y-planted or organically fertilized 

 ponds. Some authors erroneously classify them as plankton forms, although they will dwell, 

 now and then, upon solid objects. 



Pauly. T/tiO investigated eutrophic ponds, found In carp ponds permanently prevalent 

 pure plankton forms, such as the following: Bosmina longlrostria. species of Diaptomus and 

 of Cyclops (also their larvae, the Naupl j ae ) . Occasionally the following also are present: 

 Diaphanosoma bracbyurum. Daphne longispina . flerlodaphnia and Polyphemus pedi cuius . Ceriod- 

 aphala especially is a typical representative of pond plankton, while other fonns, prevalant 

 in lakes (for instance Bythotrephes ) are always absent in ponds. Therefore, we can really 

 speak of a typical "pond" plankton. 



Oligotrophic ponds are characterized by an abundance (between the middle of May to the 

 middle of September) of the dustlike, upon detritus feeding clsulocerae . On the other hand, 

 Rotlferae are almost completely absent and Copepodae very rare. Animal plankton forms abound 

 in summer. 



Eutrophic ponds develop—during the sunmer semester — aside from vast masses of vegetable 

 plankton, great numbers of Botiferae. and which, according to Naumann devour great quantities 

 of dwarfed forms of vegetable plankton, without hindrance by larger plankton plants. 



TMle diptomus forms play a greater role, here, than In cUgotrophlc ponds, the amount 

 of animal summer plankton is small in foods tuff -rich ponds. 



Cladocaras become more rare ^en ponds go eutrophic, since their productivity is hampered 

 by vegetable plankton. Exception is to be made, though, for strongly organically fertilized 

 ponds, where Daphne and Sida forms get the upper hand in the beginning and retain it for some 

 time. 



Molluaks 



S mal l and lai^e mud snails ( Llrmae stagialla . J^. auricularia . J^, ovata and L. glabra) . 

 also small plate snails ( Planorbis vortex , g.. albus and more rarely £. contortusT are found 

 in almost every pond a short time aTter cultivation. 



Scarce are Bithynia tentaculata. Valvata piscinalis. Physa fontinalis and' other snails. 



Nordquist and Jeamefeldt mention Llnnae peregra in Swedish and Finnish ponds. This 

 snail regularly invades trout ponds in Germany and multiplies extraordinarily within a short 

 tlioe. 



32 



