FISHERY BULLETIN: VOL. 73, NO. 4 



Figure 6. -Distal part of first thoracic leg (maxilliped) showing 

 diagnostic features of species of Nemato.icelis: a, N. microps; b, N. 

 atlantica; c, N. gracilis; d, N. tenella; e, N. difficilis; f, N. 

 megalops. da, dactylus;pr, propodus. 



11, 



111. 



IV. 



Distal end of lateral process always reaching far beyond distal end of proximal process; 



proximal process strongly serrated (average number of teeth 10) (Figure 7c) ... . Pacific old form 



Distal end of proximal process always reaching beyond distal end of lateral process, but not 

 reaching distal end of median lobe; proximal process moderately serrated (average 

 number of teeth 6) (Figure 7c) Indian old form 



Proximal process extremely long, reaching far beyond distal end of median lobe. Proximal 



process without any serrations (Figure 7c) new form 



Proximal process much longer than lateral process, its distal end reaching as far as distal end 

 of median lobe. Proximal process slightly serrated (average number of teeth 3) (Figure 

 7c) intermediate of old and new forms 



The two forms of N. gracilif< can also be 

 separated with certainty by plotting the ratio of 

 the proximal process to the median lobe of petas- 

 ma against carapace length (Figure 10). The in- 

 termediate forms represent the presumed in- 

 tergradation of new and old forms, although they 

 appear to be much closer to the old form than to the 

 new form with respect to this character. The 

 difference in body lengths between old forms of 

 the Indian and Pacific oceans is also apparent from 

 this figure. Table 3 shows results of an analysis of 

 covariance on proximal process of the petasma and 

 carapace length of N. gracilis old and new forms. 

 Length of the proximal process of petasma of the 

 old form is significantly different statistically 

 from that of the new form. Body lengths of the old 

 forms in the Pacific and Indian oceans are sig- 

 nificantly different statistically. Both in- 

 termediate and new forms are smaller than the old 



forms. Lengths of both the median lobe and lateral 

 process are also different in these forms. 



Of the 55 morphological characters measured, 

 many showed statistically significant differences 

 between species pairs. For example, the following 

 characters of A^. gracilis were different from those 

 of N. microps: basal length of keel; length of car- 

 pus of first thoracic leg; lateral length of carapace; 

 length of carapace between apex of keel and its 

 posterolateral margin; length of carapace between 

 apex of keel and point above photophore on 

 seventh thoracic segment; distance between pho- 

 tophore on coxa of second thoracic leg and pho- 

 tophore on coxa of seventh thoracic leg; lengths of 



Figure 7.-Petasmae of Nematosceltn: a, N. megalops;; b, N. 

 difficilis; c, N. gracilis forms. Ip, lateral process; ml, median lobe; 

 pp, proximal process; ssp, spine-shaped process; tp, terminal 

 process. 



806 



