170 



S. OHTSUKA, G.A. BOXSHALL AND H.S.J. ROE 



Fig. 44. Cladogram depicting relationships among arietellid genera. 



shifts in habitat utilization during the evolutionary history of 

 the family. Substitution of habitat type (Fig. 45) onto the 

 cladogram shown in Fig. 44 indicates that the Arietellidae 

 originated in the hyperbenthic zone. The most plesiomorphic 

 representatives of both lineages still inhabit this zone. The 

 Metacalanus-gwup has largely remained in the ancestral 

 hyperbenthic habitat although it has successfully colonized 

 anchialine caves (Ohtsuka et al., 1993a) and at least one 

 species of Metacalanus is epipelagic. In contrast, the most 

 apomorphic representatives of the Arietellus-group, the gen- 

 era Arietellus and Paraugaptilus , have successfully colonized 

 the open pelagic realm. 



A similar analysis of habitat utilization was performed on 

 the genera of the copepod family Misophrioidae by Boxshall 

 (1989). The 10 genera of this family were placed in two 

 lineages, both of which originated in the deep-water hyper- 

 benthic zone. The first offshoot of the Archimisophria- 

 lineage, represented by the genus Archimisophria Boxshall, 

 1983, has remained in the ancestral habitat but all the derived 

 representatives of this lineage are found in anchialine caves 

 and crevicular habitats. The most plesiomorphic representa- 

 tive of the Misophria-Mneage, the genus Misophriopsis Box- 

 shall, 1983, also inhabits the hyperbenthic zone but other 

 members of the lineage have successfully colonized the 

 pelagic zone, the shallow- water hyperbenthic zone and, inde- 

 pendently, anchialine habitats. 



There are interesting parallels between the Arietellidae 

 and Misophriidae. The ancestry of both families appears to 

 be closely associated with the deep-water hyperbenthic zone. 

 Plesiomorphic genera in both families have remained in the 

 ancestral habitat but more derived representatives now utilize 

 a broader spectrum of habitat types, including the shallow- 



er assarietellus 

 Paramisophria 

 Metacalanus 

 Pilarella 



Arietellus 



Paraugaptilus 



Scutogerulus 



Paraugaptiloid.es 



Sarsarietellus 



Campaneria 



water hyperbenthic zone, the open pelagic realm and anchia- 

 line caves. Certain habitat shifts appear to have occurred at 

 least twice, independently, within these two families. The 

 colonization of anchialine habitats appears to have taken 

 place twice in the Arietellidae, once within Metacalanus and 

 once within Paramisophria, just as Boxshall (1989) found for 

 the Misophriidae. Arietellids appear to have invaded the 

 open pelagic zone three times (the Arietellus- Paraugaptilus 

 group, Paraugaptiloides , and within the genus Metacalanus). 



Key to genera of the family Arietellidae 



la Leg 1 with 1 outer spine on third exopod segment 2 



lb Leg 1 with 2 outer spines on third exopod segment 3 



2a Maxillule with 5 spines and 1 process on praecoxal arthrite; 

 maxilla with 1 seta on distal praecoxal endite; caudal seta II 

 developed; genital double-somite (9) with paired genital sys- 

 tem, each copulatory pore opening within slit-like genital slit, 

 shared with gonopore Scutogerulus Bradford , 1 969 



2b Maxillule with 5 spines and 1 process on praecoxal arthrite; 

 maxilla with 2 seta on distal praecoxal endite; caudal seta II 

 developed; genital double-somite ($) with paired genital sys- 

 tem, each copulatory pore opening within common genital 

 aperture, shared with gonopore Pilarella Alvarez, 1985 



2c Maxillule with 0-2 elements on praecoxal arthrite; maxilla with 

 2 setae on distal praecoxal endite; caudal seta II reduced; 

 genital double-somite ($) with gonopore and copulatory pore 

 separate and located posteriorly Metacalanus Cleve, 1901 



3a Maxillule with 6 setae on coxal epipodite 4 



3b Maxillule with 8-9 setae on coxal epipodite 5 



