FISHERY BULLETIN: VOL. 73, NO. 4 



B 



a 



e 



1.0 m m 



B 



Figure \.—A , antenna (ventral view) and B, eye (lateral view) of Nematoscelis: a, N. gracilis; b, N. atlantica; c, N. microps; d, N. tenella; 

 e, N. difficilis;/, N. megalops. en, endopod; sc, scale; sp, spine on proximal segment of protopod; ul, upper lobe; II, lower lobe. 



The present study shows that there are two dis- 

 tinct forms in Nematoscelis (jracilis. They are 

 distinguished as ecophenotypes and are referred 

 to here as the "old form" and the "new form." The 

 old form is identical in morphological characters 

 with the typical form described by Hansen (1910) 

 from the waters of the Indo-Australian 

 Archipelago, and the new form is distinguished 

 from the typical form on the basis of 

 morphological differences on the proximal process 

 of the petasma. There is also an apparent size 

 difference between the two forms: Body length of 

 the old form is significantly larger than that of the 

 new form (cf. Figure 5a, b). The upper lobe of eye 

 in the new form is slightly narrower than that in 

 the old form. Both forms are distinguishable only 



as adults. The old form occurs mostly in the 

 northern section of the tropical Indo-Pacific 

 subregion and has maximum abundance in the 

 oxygen-poor waters of the Arabian Sea, Bay of 

 Bengal, and eastern tropical Pacific Ocean. The 

 new form occurs in the region of the South Equa- 

 torial Current. Along the equatorial zone, where 

 the two forms overlap, an "intermediate" of the 

 two forms, with regard to the length of the 

 proximal process of petasma, is also encountered. 

 Geographical distributions of these forms are 

 described in Gopalakrishnan (1974). There are ap- 

 parent morphological differences between the old 

 forms of the Indian and Pacific oceans. The 

 following key is prepared for identifying the 

 forms of A^. gracilis: 



804 



