114 



S. KARAYTUG AND G.A. BOXSHALL 



in Figure 3B). First endopodal segment with spinular row near base 

 of inner distal seta caudally (arrowed in Figure 3B). 



Labrum with 3 spinules at either side of free posterior margin 

 (arrowed in Figure IE). Mandible with spinular row near base of 

 gnathobasic blades (arrowed in Figure IF). Maxillule with 

 proximalmost spine ornamented with spinules (arrowed in Figure 

 1 A). Maxilla (Figure 1 D) with praecoxa bearing spinular row dorsally 

 and with spinular row on outer margin. Coxa with scattered spinules 

 along outer edge. Syncoxa of maxilliped without spinules near base 

 of 3 setae (arrowed in Figure IB); basis with spinular row on anterior 

 surface and 2 diffuse groups of spinules on posterior surface. First 

 endopodal segment with 2 tiny spinules on anterior surface. Strong 

 seta fused to second endopodal segment, claw-like and ornamented 

 with spinules (arrowed in Figure IB). 



Legs 1 to 3 without mid-distal spinular row on posterior surface of 

 coxa (arrowed in Figures 4B,C; 5C). Coxae of legs 2-4 with spinular 

 row on anterior surface and with inner spine bearing large postero- 

 lateral spinule (arrowed in Figures 4A; 5A,B); basis with spinular 

 row on anterior surface near inner margin (arrowed in Figures 4A; 

 5A,B). Inner coxal seta of leg 1 semispinulose (arrowed in Figure 

 4D). Terminal endopodal segment of leg 3 with spine about half as 

 long as segment (Figure 5B). Coxa of leg 4 with complex ornamen- 

 tation on posterior surface; intercoxal sclerite with spinular rows on 

 anterior and posterior surfaces, and along distal margin (Figure 

 5A,D). 



Spine and seta formula as follows: 



Coxa 



Basis 



Exopod 



Endopod 



Legl 



0-1 



1-1 



I -1;I-1;III,5 



0-1 ;0-l; 1,1,4 



Leg 2 



0-1 



1-0 



I-1;I-1;III,I,5 



0-1:0-1; 1,1,4 



Leg 3 



0-1 



1-0 



I— 1 ;I— 1 ;III,5 



0-1:0-2:1,1,4 



Leg 4 



0-1 



1-0 



I-1;I-1;III,5 



0-l;0-l; 1,11,2 



Leg 5 (Figure 2C) with long inner spine, about 4 times as long as 

 segment; outer seta simple, just less than half as long as inner spine 

 and with spinules at base (arrowed in Figure 2C). 



Description of adult male 



Body length of specimen from England (Norfolk): 619 urn and body 

 width: 213 urn. Differing from adult female as follows: Genital 

 somite separate, ornamented with 3 complete, 1 incomplete dorsal 

 surface ridges and 4 incomplete ventral surface ridges; first, second 

 and third free abdominal somites each with 2 complete dorsal and 

 ventral surface ridges (Figure 6A.B). 



Antennule digeniculate (Figure 7A,B), indistinctly 1 6-segmented. 

 Segment 1 armed with 8 setae; setaA simple (arrowed in Figure 7E). 

 Segment 10 (= ancestral segment XV) produced on one side into 

 sheath enclosing segment 1 1 ventrally: armed with 2 setae, one of 

 which pear-shaped and constricted apically, constricted part bent 

 slightly inwards and with small terminal seta-like process, other seta 

 long and naked. Segment 1 1 bearing curved seta ornamented with 

 double row of strong denticles but not as strong as in P. fimbhatus 

 group; plus 1 naked seta (Figure 7E,F). Segment 12 armed with 

 curved seta similar to that of eleventh segment, plus short highly 

 chitinized seta. Segment 13 armed with 2 short naked setae. Seg- 

 ment 14 armed with 1 short spinulate setae proximally, 2 short naked 



setae, plus 1 modified element (Figure 7F), main part of element 

 lying along surface of segment and ornamented with longitudinal 

 ridges and small central pore. Segmental fusion pattern as follows I- 

 V, VI-VII, VIII, IX, X, XI, XII, XIII, XIV, XV, XVI, XVII, XVIII, 

 XIX-XX, XXI-XXIII, XXIV-XXVIII. 



Coxobasis of antenna with spinules near base of inner setae but 

 spinules smaller than those of female (Figure 6E). Sixth leg (Figure 

 6C) armed with 1 inner spine surrounded by spinules at base; middle 

 seta plumose and as long as inner spine; outer seta naked and about 

 half as long as inner spine. 



Variability, females. Arrangements of spinules on anal cleft 

 may vary (Figure 2D). Coxobasis of antenna sometimes with extra 

 spinular row on caudal surface (Figure 3D). 



Differential diagnosis, female. P. affinis is distinguished from 

 other Paracyclops species by the combination of its 1 1 -segmented 

 antennule; the surface ridges on the urosomal somites, the spinular 

 ornamentation of the anal cleft, and the presence of 1 seta on the 

 second endopodal segment of leg 4. 



P. affinis and P. canadensis are very closely related, but P. affinis 

 can easily be differentiated from P. canadensis by the possession of 

 three spines on the terminal exopodal segment of leg 3 (Figure 5B), 

 by the presence of spinules at the base of the outer seta of leg 5 

 (arrowed in Figure 2C); by having fewer surface ridges on the 

 genital, second and third free abdominal somites (Figure 2A,B); by 

 the spinular row not extending either side of anal cleft (Figure 

 2B,D); by the structure of the inner coxal spines of legs 2 to 4; and 

 by the presence of a spinular row on the anterior surface of the basis 

 of legs 2 to 4 near to the inner margin (Figures 4A; 5A,B). 



Remarks and comparisons 



Historically there has been some disagreement about the taxonomic 

 position of P. affinis. This species was originally published by Sars 

 (1863) under the name Cyclops affinis and this name was used by 

 several subsequent authors (Brady, 1878, 1892; Vosseler, 1886; 

 Schmeil, 1892; Van Douwe, 1909) even though Sars (1863) did not 

 mention the ornamentation of the caudal rami and did not include 

 any drawings in the original publication. Rehberg (1880) described 

 Cyclops pygmaeus as a new species on the basis of the length of the 

 caudal setae and the ornamentation of the caudal rami which he used 

 to distinguish it from C. affinis. C pygmaeus was regarded by Sars 

 (1913-18) as a synonym of C. affinis and is here also considered to 

 be a synonym of P. affinis. Claus (1893a) placed C. affinis in a new 

 subgenus, Heterocyclops on the basis of the pattern of development 

 of the antennule. Later Sars (1913-18) included C. affinis in a new 

 genus, Platycyclops, but ignored or overlooked earlier work by 

 Claus (1893). Platycyclops is a synonym of Paracyclops Claus, 

 1 893. The inadequacy of Sars's description of C. affinis (Sars, 1913- 

 18) prompted Lowndes (1932) to redescribe C. affinis, correcting 

 some errors in Sars's descriptions. Harada (1931) distinguished P. 

 sitiseiensis from P. affinis on the basis of the proportional length of 

 the spines of leg 4 and the stronger inner spine of leg 5, however, 

 these characters are not significantly different from P. affinis des- 

 cribed herein. Therefore P. sitiseiensis is regarded as a synonym of 

 P. affinis, as already indicated by Monchenko (1974). The length of 

 the inner spines of fifth and sixth legs of male P. affinis from Lake 



Table 1 Body length (BL) and width (BW) measurements (in urn) of P. 



affinis 



from various 



localities (N = number of specimens 



measured) 





Locality 



Sex 



BL (mean ± SD) 





Range 



BW(mean ± SD) 



Range 



N 



England (Ringmere) 

 England (Norfolk) 

 Sweden (Upsala) 



9 

 9 

 9 



709 ± 12 

 692 ± 20.2 



827 ± 60 





684-723 

 657-731 

 753-877 



267 ±5.5 

 261 ±11.7 

 269 ± 7.8 



254-272 

 244-281 

 262-277 



10 

 13 

 4 



