PHYLOGENY OF ARIETELLID COPEPODS 



165 



similis, P. buchani, P. bermudensis (Deevey, 1973) and P. 

 meridionalis {= P. buchani sensu Sars, 1924, 1925). In 

 contrast, males of P. similis and P. bermudensis are relatively 

 plesiomorphic in that compound segment VIII-X retains a 

 seta which is derived from ancestral segment VIII. 



In contrast to the exopodal segmentation, the endopods of 

 arietellids are constantly 2-segmented with the second to 

 fourth ancestral segments almost completely fused. The first 

 segment bears a single minute seta in Crassarietellus, Cam- 

 paneria, Paramisophria, Metacalanus and Pilarella, and is 

 unarmed in Paraugaptiloides, Arietellus, Paraugaptilus, Sar- 

 sarietellus and Scutogerulus. The number of inner setae on 

 the second compound segment is variable: 3 in Crassarietel- 

 lus, Campaneria, Paramisophria, Sarsarietellus, Scutogerulus 

 and Pilarella; 2 in Paraugaptiloides, Arietellus, Paraugaptilus 

 and Metacalanus (Paraugaptilus has 1 or 2 setae on it). The 

 number of terminal setae on the compound segment is 6 in 

 Paraugaptiloides, Arietellus, Paramisophria, Paraugaptilus 

 and Sarsarietellus, and 5 in Crassarietellus, Campaneria, 

 Metacalanus, Scutogerulus and Pilarella. 



Sexual dimorphism is found in the antennary rami of 

 Arietellus and Paraugaptilus. The reduction of one of the 2 

 medial setae on the second endopodal segment of Arietellus 

 and some species of Paraugaptilus is retained only in the 

 female. In Paraugaptilus the relative length of the first and 

 second endopodal segments is different in the sexes. In 

 addition, some species of Paraugaptilus (Deevey, 1973; 

 present study) exhibit sexual differences in the exopod in that 

 the ancestral segment VIII is completely fused with segment 

 IX-X in the female and is unarmed, but incompletely fused 



with the compound segment and carrying 1 seta in the male. 

 The male shows a more plesiomorphic state in antennary 

 rami than the female. 



8. Mandible. Arietellids are typically carnivorous, feeding 

 on copepods and other small organisms (e.g., Ohtsuka & 

 Mitsuzumi, 1990; Ohtsuka et al., 1991). Their mandibular 

 gnathobases are well developed and heavily chitinized, with 

 three or four sharp teeth. 



The endopod is either reduced to 1 segment with 1 or 2 

 setae, or is unarmed and completely fused with the basis. The 

 more plesiomorphic state is retained in Crassarietellus, Cam- 

 paneria, Paraugaptiloides, Paramisophria. Metacalanus, Sar- 

 sarietellus, Scutogerulus and Pilarella, and the derived state 

 found in Arietellus and Paraugaptilus. 



The first exopodal segment has a normally developed seta 

 in all genera, except for some species of Arietellus and 

 Paraugaptilus. In these two genera this seta is sexually 

 dimorphic. The males are furnished with a normally devel- 

 oped seta, whereas the females bear a vestigial seta (Sars, 

 1924; Deevey, 1973; present study). On the fifth exopodal 

 segment, the remarkable reduction of the outer terminal seta 

 is exhibited only by Arietellus (Figs 13D,18B) and Paraugap- 

 tilus (Fig. 32B). 



9. Maxillule. Arietellids exhibit a wide variety of trans- 

 formed states in the praecoxal arthrite, the coxal endite and 

 epipodite, the basal endite and the endopod. These charac- 

 ters were used to define some arietellid genera by previous 

 authors such as Sars (1903), Rose (1933), Brodsky (1950), 

 Campaner (1977) and Ohtsuka et al. (1993a). 



The maximum number of elements on the praecoxal arth- 



B 



H 



X / 



IX 



VIM 



VII 



VI 



IV 



II 



/ 



L 



/ 



/ 



/ 



/ 



L 



L 



L 



L 



L 



L 



L 



L 



L 



L 



L 



L 



/.... 



/ 



7 



L 



L 



/ 

 L 



L 



L 



L 



L 

 L 



L 



L 



J 

 / 

 / 

 / 



Fig. 41. Schematic illustration of fusion patterns and armature of antennary exopods of the arietellid genera. A, Hypothetical calanoid 

 ancestor; B, Crassarietellus; C, Paramisophria giselae; D, Campaneria, Paraugaptiloides, Paramisophria japonica, Sarsarietellus, 

 Scutogerulus; E, Metacalanus; F, Arietellus; G, Paraugaptilus similis, male; H, P. similis, female. Solid and dotted lines indicating complete 

 separation between segments, and incomplete fusion or suture between segments, respectively. 



