84 FRESHWATER ANIMALS 



die pecten of the postabdominal claw. Either the teeth of this 

 pecten were much larger than those of the proximal and distal 

 pectens, the "pulex" criterion, or they were the same size as 

 those of the other pectens, the "longispina" criterion (see Fig. 

 8). However, classifying species on the basis of a single charac- 

 ter, while often convenient, frequently, if not usually, fails to 

 indicate the phylogenetic relationships between these species. 

 It has become increasingly apparent that Wagler's simplified 

 classification of Daphnia does not avoid this pitfall. 



We can possibly appreciate the results of these taxonomic 

 philosophies, which we might call the "polynomial" and the 

 "simplified," where they have both been used to classify the same 

 assemblage of forms. In 1950 Kiser applied the polynomial phi- 

 losophy to the North American Daphnia. His classification named 

 51 entities. These comprised four species, 14 "subspecies," and 

 33 "forms." His Daphnia pulex consisted of seven subspecies, 

 three of which have one, three, and five forms, respectively. His 

 Daphnia longispina is composed of six subspecies, four of which 

 have four, six, six, and eight forms, respectively. Pennak (1953) 

 divides the North American Daphnia into the same four species. 

 He considers that Daphnia pulex and Daphnia longispina are 

 each highly variable species, but that little is gained by naming 

 the more distinctive forms of each. However, the systems of 

 classification of both Pennak and Kiser are basically the same, 

 because each places primary emphasis on variation in a single 

 character, the relative size of the teeth in the middle comb of 

 the postabdominal claw. Detailed study has revealed that there 

 are six North American species that would be considered Daph- 

 nia pulex in either of the previously mentioned classifications 

 (D. pulex Leydig, D. middendorffiana Fischer, D. sch0dleri Sars, 

 D. catawba Coker, D. parvula Fordyce, D. retrocurva Forbes); 

 and seven that would have been considered D. longispina (D. 

 ambigua Scourfield, D. longiremis Sars, D. rosea Sars, D. laevis 

 Birge emend. Brooks, D. duhia Hcrrick emend. Brooks, D. gale- 

 ata mendotae Birge, D. thorata Forbes). Interestingly, D. longis- 

 pina O. F. Miiller, originally described in Europe, docs not occur 

 in North America. Examination of Figs. 8 and 9 will reveal some 



