the tip of the process appears to be divided 

 into two minute points. The rostrum consists 

 of two slender filaments. The mandibular palp 

 (fig. 3) is uniramous and has 4 segments; the 

 distal segment has 2 long plumose setae. The 

 mandibular blade is armed with 5 rostral teeth 

 (fig. 4). The fifth leg (fig. 5) has a long seta 

 on the posterior surface of the basis that ex- 

 tends beyond the end of the exopod. This seta 

 is much longer than that figured by Sars 

 (1925). 



This species has been recorded from the 

 Azores and oflF Gibraltar by Sars (1907, 1925) 

 and from the Great Barrier Reef by Farran 

 (1936). 



FAMILY ARIETEl.LIDAE 



Arietellus aculeattis (T. Scott, 1894) 

 (Plate 12, figs. 6-16) 



Rhincala)ius aculeatus T. Scott, 1894, p. 31, 

 plate 2, figs. 11-24. 



Arietellus setosus Giesbrecht and Schmeil, 

 1898, p. 124. 



Arietellus aculeatus, A. Scott, 1909, p. 143, 

 plate 44, figs. 4-7; Farran, 1929, p. 270; Wil- 

 son, 1950, p. 165. 



Occurrence 



Sta. 3. 1 adult male, 3.60 mm.; 



1 fifth copepodid male, 2.90 mm. 



This species was originally erected on the 

 basis of a single immature male from the Gulf 

 of Guinea and placed in the genus Rhi)icalavus 

 (T. Scott, 1894). Afterward it was made a 

 synonym of Arietellus setosus by Giesbrecht 

 and Schmeil (1898). A. Scott (1909) found a 

 single mature female in the Siboga plankton. 

 Upon this female and the immature male, A. 

 Scott reestablished his father's species. Farran 

 (1929) reported a mature male from off New 

 Zealand but gave no detailed description. The 

 following description is from an adult male ref- 

 erable to this species in the present collections. 



Description of Male 



The total length is 3.60 mm. The proportions 

 of the prosome to the urosome are 4:1. The 

 fir.st metasomal segment is separated from the 

 cephalosome, but the fourth and fifth meta- 

 somal segments are completely fused. The fore- 



head has a very strong spiniform process, 

 which is curved slightly downward in lateral 

 aspect (fig. 7). The rostrum is composed of 

 two slender filaments, which are almost hidden 

 between the basal portions of the antennules. 

 The spiniform projections of the last metasomal 

 segments are slightly asymmetrical and rather 

 divergent, but the tips are curved slightly in- 

 ward. Of these projections the right one is 

 slightly longer, reaching to the middle of the 

 fourth urosomal segment (fig. 6). The urosome 

 is 5-.segmented ; the second to fourth .segments 

 are of nearly equal length. 



The left antennule is modified for grasping 

 the female and is 19-segmented. Figure 8 shows 

 the arrangement of the setae and aesthetes. 



The antenna (fig. 9) is composed of a rather 

 small basipod, a 2-segmented endopod, and a 6- 

 segmented exopod. The endopod is longer than 

 the exopod ; both are slender. 



The mandibular palp (fig. 10) lacks an 

 endopod; the basis is longer than the exopod. 

 The mandibular blade (fig. 11) is armed with 

 4 large teeth, 3 of which are grouped. 



The maxillule (fig. 12) has 2 inner lobes, of 

 which the first has 5 spines and the second a 

 single spine. The single outer lobe has 8 setae. 

 The exopod is relatively large, with 3 setae at 

 the apex. The endopod is absent. 



The maxilla and maxilliped are similar to 

 those of A. setosus as figured by Giesbrecht 

 (1892). 



The coxa in the first pair of legs (fig. 13) 

 has an internal seta, and the basis has an inter- 

 nal and an external seta. The endopod is 3- 

 segmented ; the first segment has 1 internal 

 seta, the second segment 2 internal setae, and 

 the third segment 2 internal setae, 1 external 

 seta, and 2 terminal setae. The exopod is also 

 3-segmented ; the first and second segments each 

 have 1 external spine and 1 internal seta. The 

 third segment has 4 internal .setae, 2 external 

 spines, and a terminal spine. 



The basipod of the .second leg (fig. 14) has a 

 single seta on the internal margin of the coxa. 

 The endopod is 3-segmented ; it has 1 internal 

 seta on the first segment, 2 internal setae on 

 the second segment, and 8 setae on the third 

 .segment. The exopod is also 3-segmented ; the 

 fir.st and second segments each have 1 internal 

 .seta and 1 slender, curved external spine. The 



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U.S. FISH AND WILDLIFE SERVICE 



