FISHERY BULLETIN: VOL. 71, NO. 4 



ever, they occupy a discrete position relative 

 to the remainder of the sites on the segment. 

 This class of variation also deserves increased 

 attention as a potential fine scale indicator of 

 intrapopulation genetic variation. 



Thus for application of integumental organs 

 to copepod systematics at or above the rank of 

 species, variation encountered during this study 

 appears to be of no consequence. Moreover, the 

 intraspecific variability observed may on the 

 basis of experience with subteiiuis provide a 

 dependable, measurable source for studying 

 population homogeneity and gene flow. 



PERFORATION SITES 

 IN THE GENUS 



Intra- and interspecific comparisons of per- 

 foration number and arrangement are facili- 

 tated by compelling evidence that sites similar 

 in location and associated organ (i.e., gland 

 pore or sensilla type) within and between species 

 are homologous. Tables 3 and 4 and figures of 

 individual species summarize the evidence that 

 in general perforation number and topographic 

 arrangement are essentially constant and 

 characteristic for each species. Further, all of 

 the available observations indicate that the 

 type of organ found at any particular perfora- 

 tion site is also constant. 



As shown below, constant differences in num- 

 bers and arrangement of perforations between 

 the morphologically more similar species are 

 small. Quantitative and topographic differences 

 are correspondingly greater between species 

 that are more dissimilar morphologically (e.g., 

 Figures 9, 11, 13, 15). However, the total num- 

 ber of perforation sites in the genus appears to 

 be about two times the number found in any 

 one species (Figure 5). 



To construct Figure 5 an assessment of the 

 extent of interspecific homology in sensilla and 

 pores of Eucalanus was obtained by rigorous 

 comparison of all the species segment by seg- 

 ment. The tabulation was restricted to desig- 

 nated sites, i.e., those occun-ing in 10% or more 

 of the specimens of each species. As described 

 above, sites are judged to be homologous if they 

 occur on the same segment in the same general 

 position relative to the pattern characteristic 



of the segment and represent the same kind of 

 organ (gland pore or type of sensilla). The place 

 of insertion of the segment's paired appendages 

 and the topographic position relative to the 

 other sensilla and gland pores of the segment 

 aid in locating perforation sites. Overlaps of 

 camera lucida sketches were also helpful when 

 allowance was made for relative and absolute 

 differences in size. Allowance was also made 

 for small-scale variation of one or two perfora- 

 tions relative to another one or a set as in peg 

 and pore pairings; small differences in the 

 spacing between adjacent sites and rotation of 

 one site relative to another was observed fre- 

 quently within the general pattern arrangement 

 of individual species. 



The analysis reveals 163 different dorsal pore 

 and sensilla sites and 30 lateral sites on each 

 side of the body. The total number of different 

 sites within the genus (223) is less than twice 

 that of the species with the highest individual 

 score (Table 3). Thus most sites in the genus 

 appear to be common to many of the species and 

 an appreciable number is common to all (Figure 

 6). 



Examination of small numbers of copepodid 

 stages IV and V, adult males of all species and a 

 few specimens of copepodid stage III indicated 

 conformity of each to the pattern characteristic 

 of the species, except for segments that undergo 

 sexual modifications in the process of matura- 

 tion. 



PERFORATION NUMBERS AND 



PATTERNS AMONG THE SPECIES 



GROUPS 



Interspecific comparison of the perforations 

 observed in Ei(cakuius is, as already mentioned 

 above, greatly simplified by the not unreasonable 

 assumptions that repetitious similarities in 

 pattern are dependent upon and a direct reflec- 

 tion of genetic similarities. With this as a 

 working hypothesis, reducing and assimilating 

 the distribution of perforation sites was enhanced 

 by assembling similarities among the different 

 species and by using for comparisons all other 

 constant topographic features of the integument. 



All the species have in common 37 tergal 

 sites, best seen in dorsal view and 9 pleural sites 



980 



