FISHERY BULLETIN: VOL. 72, NO. 1 



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28 30 32 34 36 



LENGTH OF RIGHT A1 SEGMENT 18, mm 



Figure 32. — Length of right furcal ramus (ordinate) 

 plotted against length of segment 18 of right Al (abscissa) 

 for males of the four species of Puiitellina. 



the proximal end of the sac cemented to the 

 right side of the genital segment, morii and 

 sobrina in a virtually identical fashion, differing 

 somewhat from the condition found in platychela. 

 In plumata, however, attachment is restricted 

 to the proximal end of the neck, the remainder 

 of the neck and the entire sac hanging free from 

 the body but showing helical convolutions 

 similar to those present in the other congeners. 



Geographical Occurrence 



Three of the species, morii, sobrina, and platy- 

 chela, were found primarily in low latitudes 

 between 20°N and 20°S (Figures 8, 12, 15). 

 The three species are essentially allopatric to 

 one another, each predominating in a geograph- 

 ically different segment of equatorial circulation 

 in the world's oceans (see Table 20). Relatively 

 high frequencies of abundance or occurrence 

 coincided with eutrophic equatorial regions 

 characterized by a shallow O2 minimum layer 

 (^1 ml/liter) lying at or near the permanent 

 thermocline. The three species tend to concen- 

 trate in the uppermost 20 to 30 m of depth and 

 virtually disappear below 50 m (in preparation). 



The fourth sibling, plumata, is widespread in 

 subtropical latitudes (Figure 5) and may be 

 locally abundant in tropical regions downstream 

 from areas of persistent upwelling. It is the 



only species of the genus with a circumglobal 

 range but tends to be infrequent to absent in 

 tropical areas dominated by its equatorial 

 cognates (see Table 20). Its vertical distribution 

 appears to encompass the surface to 200-m 

 depth in subtropical latitudes, the lower limit 

 shoaling to about 100 m in tropical latitudes 

 (in preparation). 



Summation of Ph> logenetic 

 Similarities 



Thus within the framework of the 17 charac- 

 ters considered above, morii and sobrina show 

 the highest frequency of similar character 

 states. In practice their overall morphological 

 similarity is sufficient to require routinely 

 close inspection at appreciable magnifications 

 for reliable separation. Though the next most 

 frequently linked pairing, plumata and platy- 

 chela, show similarity in about 60% of the 

 features in Table 9, at low magnifications under 

 a stereomicroscope they are almost as distinct 

 from one another as each is from motii or 

 sobriiia. 



As noted in the calanoid genera, Labidocera 

 and Clausocalaiius (Fleminger 1967b; Frost 

 and Fleminger, 1968), the distinguishing 

 features of the sibling species in Pontellina are 

 limited to sexually modified characters, i.e., 

 the fifth legs, the genital segment, the posterior 

 corner of ThIV-V, the male right Al, and 

 the caudal furca. 



There is reason to regard plumata as re- 

 taining the strongest similarity to the Pontellina 

 ancestral stock. This view rests upon two fea- 

 tures: the slightly stronger resemblance of 

 sexually modified structures in plu //m^o, especial- 

 ly the ThIV-V spine in the female, to those of 

 Poiitellopsis and of the more eurytopic circum- 

 global distribution of plumata in comparison to 

 the restricted distributions of its equatorial 

 congeners. 



To examine the statistical significance of the 

 phylogenetic relationships inferred from the 

 characters given in Table 9 we have utilized a 

 computer program that detects significant 

 levels of co-occurrence among sets of overlapping 

 functions. The program has been informative in 

 the detection of communities as well as in 

 systematic classifications of flexibacteria (Fager, 

 1969). 



100 



