SYSTEM ATICS AND PHYLOGENY OF ZAUSODES 



117 



Table 1 Segmentation of 9antennule (Al) and antennary exopod (A2), armature formula of antennary exopod and swimming legs P2-P4 in Perissocope 

 (2 species) and 12 species of the Zausodes complex. The swimming leg armature formulae of Z. cinctus Krishnaswamy and P. adiastaltits Wells have 

 been corrected (see text). 







Seg 



mentation 







Armature 













Al 



A2 



A2 



P2 



P: 





P4 



arenicolus 





8 



1 



2 



0.1.223 



0.1.221 



0.1.323 



1.0.221 



0.1.323 



1.0.121 



areolatus 





6 



1 



2 



0.1.223 



0.1.221 



0.1.323 



1.221 



0.1.323 



1.121 



biarticulatus 





8 



2 



(2+2) 



0.1.223 



0.1.221 



0.1.323 



1.1.221 



0.1.323 



1.221 



cinctus 





7 



1 



2 



0.1.223 



0.1.221 



0. 1 .323 



1.1.221 



0.1.323 



1.1.221 



cookorum 



[9] 

 [cf] 



8 



2 



(2+2) 



0.1.223 



0.1.221 



0.1.323 



1.0.221 



0.1.322 

 0.1.323 



1.221 



kirstenae 



[9] 

 [cf] 



8 



2 



(2+2) 



0.1.223 



0.1.221 



0.1.323 



1.0.221 



0.1.322 

 0.1.323 



1.0.221 



limigenus 





7 



1 



2 



0.1.223 



0.1.121 



0.1.323 



1.0.221 



0.1.323 



1.121 



paranaguaens 



is 



7 



1 



2 



0.1.223 



0.1.120 



0.1.323 



1.0.221 



0.1.323 



1.121 



septimus 





8 



1 



2 



0.1.223 



0.1.221 



0.1.323 



1.0.221 



0.1.323 



1.121 



sextus 





7 



1 



2 



0.1.223 



0.1.221 



0.1.323 



1.0.221 



0.1.323 



1.121 



shulenbergeri 





7 



1 



2 



0.1.223 



0.1.121 



0.1.323 



1.0.221 



0.1.323 



1.121 



stammeri 





7 



1 



2 



0.1.223 



0.1.121 



0.1.323 



1.0.221 



0.1.323 



1.121 



Perissocope 























adiastaltus 





7 



3 



(2+0+3) 



0.1.223* 



0.1.221 



0.1.323 



1.1.321 



0.1.323 



1.1.121 



biarticulatus 





8 



3 



(1+0+3) 



1.1.223 



0.1.221 



1.1.323 



1.1.321 



1.1.322 



1.1.221 



* Wells (1968) figured P2 exp-3 with formula 323; this is clearly based on an aberrant specimen since no extant harpacticoid has more than 7 elements on 

 this segment (Huys & Boxshall, 1991; also confirmed by re-examination of other type material). 



setae on exp-2. Comparison with the 3-segmented exopod in 

 Tighopus suggests that the proximal lateral seta on exp-2 in these 

 genera originates from the incorporated middle segment and there- 

 fore the ancestral setal formula must have been [2,1 ,3]. In Perissocope 

 the lateral seta on exp-2 is lost resulting in a [2,0,3] formula in P. 

 adiastaltus Wells or [ 1 ,0,3] in P. biarticulatus Watkins. Further setal 

 reduction has occurred in the Zausodes complex where only 2 setae 

 are retained on the distal segment in the most primitive species 

 (biarticulatus, kirstenae, cookorum), or secondarily, the exopod 

 became an unsegmented bisetose ramus (all other species). 



( 7) Armature praecoxal endite maxilla 



Some species of Perissocope have 5 elements on the praecoxal 

 endite of the maxilla (Huys et al., 1996; Fig. 106F) which is the 

 highest number recorded in any member of the Harpacticidae. This 

 number is reduced to four (state 1) or three setae (state 2) in the 

 Zausodes complex. Ito (1979) recorded variability in the maxilla of 

 Z. biarticulatus and regarded the 3-setae condition as the typical 

 one. The 'atypical' maxilla illustrated in his Fig. 3-1 shows 4 

 elements arranged in the same pattern as found in Z. arenicolus (Fig. 

 3B) and Z septimus (Mielke, 1990: Abb. 3A). On the basis of this 

 similarity we have scored state 1 for Z biarticulatus. Lang (1965) 

 showed only 2 setae on this endite but we suspect that the third one 

 was overlooked and have given this species a score 2 accordingly 

 (Table 3). 



(8) Armature PI exp-3 



The distal exopod segment of PI is small or vestigial in the 

 Harpacticidae and typically embedded in the distal margin of the 

 middle elongate segment. Huys et al. (1996) described the basic 

 armature of this segment as four unhinged claws, 1 hinged claw and 

 a seta, but careful re-examination of a range of genera revealed that 

 the seta in reality belongs to the middle exopod segment. This seta is 

 often small (e.g. Fig. 5C) and sited at the distal inner corner of enp- 

 2. Huys et al. 's misconception stems from observations of 

 Harpacticus and Zaus in which the distal segment is largely incorpo- 

 rated in the middle one. In other genera such as Harpacticella and 

 Tigriopus the distal segment is well delimited showing the real 



origin of the inner seta (Ito, 1970, 1977; Ito & Kikuchi, 1977). Both 

 Perissocope and the Zausodes complex deviate from the normal 

 armature pattern by the presence of two hinged (geniculate) claws 

 (see above). The modification of one of the simple claws into a 

 second geniculate one is a synapomorphy for these taxa. Species of 

 the Zausodes complex have lost one of the simple claws, retaining 

 only four elements on exp-3 (2 geniculate and 2 simple claws). 



(9) Armature PI enp-1 



Harpacticidae typically possess a well developed inner seta on the 

 proximal endopod segment of PI. The exceptions to this rule are the 

 species belonging to the Zausodes complex which have secondarily 

 lost this seta. 



( 10) Armature P2 enp-3 



Most Harpacticidae have 2 inner setae on the distal endopod seg- 

 ment of P2. Some species within the Zausodes complex possess 

 only 1 seta on this segment (Fig. 15 A; Table 1). This reduction has 

 evolved convergently in other genera such as Harpacticus (e.g. H. 

 compsonyx) and Tigriopus. 



(11 ) Armature P3 enp-2 



The inner seta on the middle endopod segment of P3 is present in 

 most harpacticid genera, including Perissocope. Within the Zausodes 

 complex, however, this seta is commonly lost and is retained only in 

 Z biarticulatus (and the imperfectly described Z cinctus - see 

 below). 



(12) Armature P3 enp-3 



Species of Perissocope and most other genera of the family possess 

 3 inner setae on the distal endopod segment of P3. Various reduc- 

 tions occur in the more advanced genera Tigriopus, Paratigriopus 

 and Discoharpacticus. All species of the Zausodes complex invari- 

 ably have 2 inner setae on this segment. 



(13) Armature P4 exp-3 



Sexual dimorphism in the number of armature elements on the P4 

 exopod is extremely rare within the Harpacticoida. In some species 



