PHYLOGENY OF ARIETELLID COPEPODS 



167 



stage of Paramisophria sp. collected from South Japan carries 

 a minute inner coxal seta (Ohtsuka et al., 1991, Fig. 6J,K). 

 The maximum setation on the third endopodal segment is 

 retained in all the genera and species except for P. galapagen- 

 sis: 2,2,2 in P. galapagensis and 2,2,3 in other taxa (Ohtsuka 

 etal., 1993a). 



15. Female leg 5. The female fifth legs of arietellids are 

 variable, as in several other calanoid families and the 

 misophrioid family Misophriidae by Huys & Boxshall (1991). 

 Campaner (1984) compared the structure of leg 5 in both 

 sexes but drew no strict homologies of segmentation and 

 armature elements. 



Fig. 42 schematically depicts apparent evolutionary trends 

 in the structure of female leg 5 within the genera Arietellus, 

 Paraugaptilus, Paramisophria, Metacalanus and Pilarella. 

 Within the genus Arietellus, three obvious evolutionary 

 trends in segmentation and setation can be recognized: 

 incorporation of the endopod into the basis, reduction of 

 endopodal setae, and fusion of coxa, basis and both rami. The 

 genus Paramisophria also exhibits two distinct evolutionary 

 trends: reduction in numbers of endopodal setae and of 

 exopodal spines. In the genus Metacalanus reduction of the 

 endopod, and fusion of both rami into the basis plus reduc- 

 tion in number of elements on the exopod occur. Based on 

 these evolutionary trends, the derivation of the Paraugaptilus 

 state from an Arietellus-Mke condition, the relationships 

 between Sarsarietellus and Paramisophria spp., and the deri- 

 vation of Metacalanus from a Paramisophria-Yike ancestor, as 

 already proposed by Campaner (1984), are supported. The 

 setation of Crassarietellus (Fig. 6K,L) suggests a close rela- 

 tionship with Paramisophria, especially in the endopod seta- 

 tion. 



Consideration of the plesiomorphic states exhibited in leg 5 

 of all female arietellids indicates that the hypothetical ances- 

 tor may be characterized by having retained a) the coxa, the 

 basis and 3-segmented exopod and 2-segmented endopod as 

 separate segments; b) basal seta present; c) intercoxal sclerite 

 separate from coxae; d) setal formula of endopod segments 

 0-2;0,l,l; and e) setal formula of exopod I-0;I-0;II,I,0. 



In Crassarietellus and Scutogerulus the endopod is dis- 

 tinctly separate from the basis, is 1-segmented, and bears 2 

 and 1 setae respectively. In Arietellus, Paramisophria, Meta- 

 calanus, Paraugaptilus, Sarsarietellus and Pilarella the endo- 

 pod is completely or incompletely fused with the basis, and is 

 represented by 0-4 setae. In Paramisophria the number of 

 setae on the endopod ranges from to 2; in Arietellus from 1 

 to 3 setae. In Metacalanus, Paraugaptilus and Pilarella the 

 endopod is represented by 0-1 seta, and is almost completely 

 incorporated into the basis. 



In P. japonica (Ohtsuka et al., 1991, Fig. 3F,G) and 

 Scutogerulus (Bradford, 1969, Fig. 181) the exopod is com- 

 posed of 2 distinct segments. Particularly in P. japonica the 

 ancestral second and third exopodal segments are incom- 

 pletely fused with a suture visible on the anterior surface. In 

 Crassarietellus (Fig. 6K,L) and Sarsarietellus (Fig. 36H) the 

 first to third exopodal segments are almost fused with a 

 suture just visible. In Arietellus (except for A. mohri and A. 

 sp.), almost all species of Paramisophria (except for P. 

 giselae), Metacalanus (except for M. aurivilli and M. acutio- 

 perculum) and Pilarella, the exopod is distinctly 1-segmented, 

 but variably armed. Arietellus carries only a single terminal 

 spine; Paramisophria bearing 2 or 3 lateral and 2 terminal 

 spines; Metacalanus has 1 terminal spine or 2 terminal and 1 

 lateral spine. The unarmed exopods of A. mohri and A. sp. 



are lobate and almost completely fused with the basis. In M. 

 aurivilli and M. acutioperculum the exopod is represented by 

 a small knob with a single terminal seta. In Paraugaptilus the 

 exopod is completely incorporated into the basis. 



The intercoxal sclerite and coxa are completely separate in 

 Sarsarietellus, Metacalanus, Pilarella and P. giselae, and 

 incompletely in Crassarietellus and Arietellus (except for A. 

 mohri and A. sp.). In Paramisophria (except for P. giselae), 

 Paraugaptilus, A. mohri and A. sp. fusion is almost or 

 completely accomplished. 



Little attention was paid to the variability within a genus by 

 Campaner (1984). Within genera such as Arietellus, Parami- 

 sophria and Metacalanus , the reduction in segmentation and 

 setation is more variable than expected. Reductions in seg- 

 mentation and setation appear to occur independently within 

 each genus. For instance, the fusion between coxa and 

 intercoxal sclerite probably evolved independently in Arietel- 

 lus (see Fig. 17) and Paramisophria (Fig. 20E,F). The num- 

 ber of elements on both rami vary widely in these genera, 

 whereas the outer basal seta is consistently present in all 

 genera and species. In Arietellus the right basal seta is slightly 

 or considerably longer than the left. 



16. Male leg 5. Campaner (1984) showed a possible rela- 

 tionship between the male fifth legs of arietellids, based 

 mainly on the presence or absence of the endopod on either 

 side. However, the homologies of segmentation and setation 

 were not considered in detail. Compared with the female fifth 

 legs, the male legs are less variable in segmentation and 

 setation within a genus. A scheme indicating possible deriva- 

 tions of segmentation and setation is given in Fig. 43. 



The hypothetical ancestral state is based on all taxa and 

 consists of a) intercoxal sclerite and coxa separate; b) coxa 

 completely separate from basis; c) basal seta present; d) 

 2-segmented, unarmed left endopod; e) 1-segmented, 

 unarmed right endopod; f) 3-segmented right and left exo- 

 pods; and g) setal formula I-0;I-1;III,I,0. The presence of a 

 basal seta and the numbers of first and second exopodal 

 elements are constant in all genera. 



Although the left endopod of Paramisophria japonica 

 (Ohtsuka et al., 1991, Fig. 4K) and the right endopod of 

 Paraugaptiloid.es (Fig. 12E) each bear a minute terminal 

 spinule, we are not certain whether it is homologous with a 

 true setation element. 



In Campaneria, Paraugaptiloid.es , Arietellus and Paraugap- 

 tilus, both right and left endopods are present. In the first 

 three genera a distinctly or indistinctly 2-segmented left 

 endopod is present, while the right endopods of all four 

 genera comprise a single segment. In Paraugaptiloides the 

 first and second endopodal segments are completely separate 

 and are accompanied by musculature, indicating that the 

 articulation between these segments is functional. In Cras- 

 sarietellus and Paramisophria (except for P. cluthae) only the 

 left endopod is retained and the right endopod is absent; the 

 former has an indistinctly 2-segmented left endopod while in 

 the latter this ramus is 1-segmented. In Metacalanus both 

 right and left endopods are completely absent. 



The most plesiomorphic state in segmentation and arma- 

 ture of the exopod is retained in Paramisophria: in both legs, 

 the third segment is separate from the second (cf. Fosshagen, 

 1968) and 4 elements are present on the third segment of both 

 legs (see Ohtsuka & Mitsuzumi, 1990, Fig. 4E,F). In Cras- 

 sarietellus and Paraugaptiloides a vestigial outer proximal 

 element is present on the left third exopod segment, which 

 carries 4 elements in total. The number of elements on the 



