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basis produced distally into a large tooth-like 

 process (Figure II). Second to foux-th legs 

 (Figures IJ-L) similar to A. pacificu.^, but coxa 

 of fourth leg without spinules at base of inter- 

 nal seta. Terminal exopodal spines of second 

 to fourth legs with 15-17 teeth. 



Male. — Body lengths of eight type specimens, 

 1.58-1.68 mm. Proportional lengths of prosome 

 and urosome about 75:25. Body slender, with 

 forehead slightly produced (Figure 2A). Ros- 

 strum reduced. Metasomal process pointing 

 straight backward, reaching about distal end 

 of genital segment (Figures 2D, E). Second 

 to fourth urosomal segments and caudal 

 rami (Figure 2E) with width: length ratios of 

 1:0.98-1.05, 1:1.08-1.15, 1:1.12-1.19, and 1:1.82- 

 2.00, respectively. Antennules reaching about 

 distal end of fourth urosomal segment, nine- 

 teenth and longest segment (Figure 2G) with 

 width: length ratio of 1:4.9-5.1. On second leg 

 (Figure 2M), endopod reaching distal end of 

 second exopodal segment. On second and third 

 legs (Figure 2N), terminal exopodal spines 

 longer than third exopodal segments, with 

 about 29 and 23 teeth, respectively. Second to 

 fourth segments of fifth leg (Figure 20) with 

 width: length ratios of 1:3.7-4.2, 1:8.3-8.7, and 

 1:9.0-9.7, respectively. 



AETIDEUS ACUTUS FARRAN, 1929 



Male. — Body length, 1.22-1.36 mm according 

 to 48 randomly selected specimens. Propor- 

 tional lengths of prosome and urosome about 

 79:21. Dorsally, forehead (Figure 3B) more 

 produced than in A. ine.vicaitufi. Rostrum re- 

 duced. Metasomal process with wide base, dis- 

 tinctly curved downward when viewed laterally 

 (Figure 3E) and slightly curved inward in 

 dorsal view (Figure 3D). Second to fourth uro- 

 somal segments and caudal rami with width: 

 length ratios of 1:0.83-0.88, 1:0.75-0.81, 1:0.78- 

 0.81, and 1:1.64-1.83, respectively. 



Antennules reaching about distal end of 

 third urosomal segment, nineteenth and long- 

 est segment (Figure 3F) with width: length 

 ratio of 1:3.31-3.52. Other cephalic appendages 

 similar to A. nie.vicanus. On second leg (Figure 

 3L), endopod reaching distal end of second 

 exopodal segment. Terminal exopodal spines of 

 second and third legs (Figure 3M) longer than 

 their third exopodal segments, with about 23 

 and 18 teeth, respectively. Terminal exopodal 

 spines of fourth legs (Figure 3N) shorter than 

 their third exopodal segments, with about 16 

 teeth. Second to fourth segments of fifth leg 

 (Figure 30) with width: length ratios of 1:3.41- 

 3.78, 1:6.72-7.33, and 1:6.00-6.60, respectively. 



Remark.'^. — The female of A. nie.vicaitus is dis- 

 tinguished from A. annatu.'i by the slender 

 body, long antennules which extend beyond the' 

 caudal rami by two segments and, particularly, 

 the fourth leg which lacks spinules at the base 

 of the coxal seta found in all other species of 

 the genus (Bradford, 1971). The male of A. 

 mexicaiius is very close to that of A. armatu.'i 

 as described by Bradford but seems to differ 

 from it in the proportions of the caudal rami 

 and of the second to fourth segments of the fifth 

 legs. However, the importance of these charac- 

 ters in the distinction between the two species 

 is yet to be determined. 



Di.'^tribHtio)i. — A. mexicaitH.'< was found in a 

 number of plankton samples taken from the 

 upper 500 m in the Gulf of Mexico by the RV 

 Alantii/os in September 1971. A. arniatus re- 

 corded from the Caribbean Sea by Park (1970) 

 belongs to this new species. 



Remarks. — The male of A. acutus was first de- 

 scribed very briefly by Bradford (1971). The 

 present specimens seem to be in agreement 

 with her descriptions. The male of A. acutus 

 is easily distinguished from those of A. niexi- 

 caiius and A. gie.sbrechti by its considerably 

 smaller size. In the shape of the forehead, meta- 

 somal process, and antennule, it is closely re- 

 lated to A. gieahrechti, but differs from this 

 species in the relative lengths of the urosomal 

 segments and caudal rami. 



The female specimens of A. acutus in the 

 present study (1.48-1.62 mm in body length 

 according to 80 randomly selected specimens) 

 are identical with the specimens described by 

 Park (1968) from the Pacific, and can be readily 

 recognized by the shape of the spermatheca 

 (Figure 3A). The appendages are similar to 

 those of A. pacificus as described by Park (1968), 

 except that the maxillule carries 3-1-3 + 6 setae 

 on the endopod. 



217 



