SYSTEM ATICS AND PHYLOGENY OF ZAUSODES 



119 



not all) species of Perissocope such as P. biarticulatus. Within the 

 Zausodes complex 2 setae are found in only four species (Table 1), 

 however in both biarticulatus and cookorum the distal segment 

 represents the fused enp-2 and -3, obscuring the origin of the 

 proximal inner seta. Comparison with the closely related kirstenae, 

 in which all segments are expressed, suggests that both inner setae 

 are derived from enp-3. 



(17) Shape P5 exopod of both sexes 



The P5 exopod is usually oval or elongate in both sexes. In one 

 species group of the Zausodes complex the exopod is distinctly 

 round (e.g. Figs 15D, 18D) which by outgroup comparison with 

 Perissocope and other genera is regarded here as the apomorphic 

 condition. 



(18) Shape P5 9 endopodal lobe 



The endopodal lobe is well developed in the majority of female 

 harpacticids, including most members of the Zausodes complex. In 

 four species (biarticulatus, kirstenae, cookorum, cinctus) the whole 

 baseoendopod is modified, forming a transversely elongated plate, 

 and the endopodal lobe is no longer expressed (Figs 23B; 30C). 



(19-20) Armature P5 9 endopodal lobe 



Species belonging to Perissocope and the Zausodes complex typi- 

 cally have 5 well developed setae on the P5 endopodal lobe of the 

 female. In some species of the latter particular elements have 

 undergone secondary reduction in size. In the cookorum-kirstenae- 

 biarticulatus group the innermost seta is rudimentary and sited at 

 the extreme distal corner near the articulation with the exopod 

 (Figs 23B, 30C; character 19 in Table 3). Further reduction has 

 occurred in biarticulatus where the three innermost setae are com- 

 pletely vestigial (Ito, 1979). In the type species Z. arenicolus the 

 3rd and 4th setae (counted from the innermost according to Huys 

 et al. (1996)) are very reduced and the innermost one is well 

 I developed. This reduction is treated separately as character 20 in 

 Table 3 and scored as state 1 in both arenicolus and Septimus. In 

 the latter one of the smaller setae is lost, retaining only 4 elements 

 on the endopodal lobe (Lang, 1965; Mielke, 1990). The reduction 

 of setae 3 and 4 in biarticulatus is regarded here as a further 

 derived state of character 19 and not as the apomorphic state of 

 character 20. 



(21) Armature antennulecf 



Male antennules in the Harpact icidae are of the subchirocer or chirocer 

 type. Armature elements are typically modified on the segments 

 located either side of the geniculation. In one group of the Zausodes 

 complex the male antennule also possesses a modified element on 

 segment 3. It is represented by a strong spine which is situated dorsal ly 

 near the distal margin of the segment (Figs 1 2F, 1 8 A). 



(22-23) Modification P2 enp-2 cf 



The male P2 endopod is of high significance in understanding the 

 phylogeny of the Harpacticidae (Ito, 1984). Many genera possess an 

 outer spinous apophysis on the middle endopod segment which 

 attains its maximum size in Harpacticus and Discoharpacticus. 

 Analysis of the phylogenetic relationships within the family (Huys, 

 unpubl.) suggests that this apophysis has become gradually smaller 

 during harpacticid evolution and was lost independently in 

 Paratigriopus, Harpacticella and Zaus-Zausopsis. A similar regres- 

 sive evolution has also been documented in the Paranannopidae for 

 a similar apophysis on the male P2 endopod (e.g. Gee & Huys, 1 99 1 ; 

 Huys & Gee, 1993, 1996). Within the Perissocope- Zausodes'' 

 lineage the apophysis is clearly in a state of reduction. The genus 



Perissocope combines both species with a slender apophysis (P. 

 biarticulatus, P. exiguus, P. bayeri) and species without such an 

 uncinate process (P. adiastaltus). Within the former Zausodes com- 

 plex only the type species Z arenicolus possesses a short spinous 

 outgrowth on P2 enp-2 (Fig. 7E) whereas all other species have lost 

 the apophysis completely (Figs 12D, 17C, 22D). 



In both kirstenae and cookorum the inner element of P2 enp-2 is 

 sexually dimorphic, being setiform in the 9 and modified into a short 

 stout spine in thecf(character 23 in Table 3; Figs 22D, 29A). 



(24) Modification P2 enp-3 cf 



The outer spine on the distal endopod segment of the male P2 is 

 frequently modified in the Harpacticidae. In male Harpacticus the 

 outer spine is usually lost at the final moult or not formed at all in any 

 male copepodid instar (Ito, 1984). In some species such as H. 

 furcatus Lang the outer spine is represented by a rudimentary setule 

 (Ito & Fukuchi, 1978). In other genera such as Tigriopus, 

 Paratigriopus and Zaus the outer spine is not sexually dimorphic 

 and articulating with the segment. A different modification is found 

 in male Perissocope where the outer spine is completely integrated 

 into the distal segment, forming a long, slender apophysis (e.g. 

 Vervoort, 1964; Pallares, 1975; Watkins, 1987; Wells, 1968). A 

 similar apophysis was found by Ito (1979) in Z. biarticulatus and in 

 two new species (kirstenae, cookorum) described here. In the latter 

 the apophysis is represented by a spinous process which is minutely 

 pectinate at the inner subapical margin and about equal in length to 

 the outer spine in the female (Figs 22D, 29A). 



(25) Modification P3 enp-2 cf 



Distinct sexual dimorphism on the P3 endopod is rare in the 

 Harpacticidae. Differences in surface ornamentation between the 

 sexes are occasionally found in Harpacticus (Ito, 1976; Ito & 

 Fukuchi, 1978) and in species of the Zausodes complex 

 (shulenbergeri, kirstenae), however, these have not been included in 

 the analysis. A more pronounced modification involves the forma- 

 tion of a mucroniform process at the outer distal corner of the middle 

 segment. This is found in the genus Perissocope and in two closely 

 related species of the Zausodes complex (kirstenae, cookorum) 

 (Figs 22E, 29D). 



Data matrix and analysis 



In order to resolve the relationships within the Zausodes complex 

 the analysis was executed at the species level. The characters used in 

 the analysis of phylogenetic relationships between Perissocope and 

 the 12 species of the Zausodes complex are listed in Table 2. The 

 character states are explained inside square brackets using the 

 multistate system: = the ancestral state, 1 = the derived state, 2 = 

 a further derived state. The scores for each character and taxon are 

 compiled in matrix format in Table 3. A question mark indicates 

 missing data, either because the appendage or structure is unknown 

 in that species (certain sexually dimorphic characters could not be 

 scored because only one sex is known) or because it was impossible 

 to score the character accurately due to the lack of detail in the 

 original descriptions (cf. Jakobi, 1954). Z. cinctus Krishnaswamy 

 was excluded from the analysis. Its status is discussed below. 



RESULTS AND DISCUSSION 



Two most parsimonious trees were obtained with tree-length 36 

 and consistency index 0.778 (Fig. 33). Both trees differ only in the 

 position of Z septimus which in tree A forms a monophyletic group 



