116 



L. BOUCK, D. THISTLE AND R. HUYS 



A first indication of the artificiality of Lang's subdivision was 

 given by Ito (1979) who noted the similarity between the shape of 

 the PI exopod of Z. biarticulatus and that of the genus Perissocope. 

 Ito did not assign his species to Perissocope because it lacked the 

 proximally-born inner seta on PI enp-1 distinctive of this genus. 

 Watkins (1987) remarked that Zausodes and Perissocope are more 

 closely related morphologically, ecologically and zoogeographically 

 than either is to any other genus of the Harpacticidae. He suggested 

 that the similar body shape between Zausodes and the other 

 Zausodinae was a product of convergent evolution, particularly as 

 the various body somites contribute differently to the overall tear- 

 drop shape, and similar convergences are found in Harpacticus 

 compressus Frost, Discoharpacticus mirabilis Noodt and 

 Perissocope biarticulatus Watkins. 



Preliminary phylogenetic analysis (Huys, unpubl.) supports a 

 robust sistergroup relationship between Perissocope and Zausodes 

 sensu lato on the basis of the following synapomorphies: 



1 . strong sexual dimorphism in the shape of the rostrum; 



2. antennule 9 with fused segments 7 and 8 (representing ancestral 

 segments XXIV and XXV) forming compound double segment 

 (see below: character 1); 



3. armature of PI exp-3 consisting of 2-3 simple (unhinged) and 2 

 geniculate (hinged) claws (see below: character 8); confirmed by 

 re-examination of the type material off! adiastaltus Wells (BNHM 

 1967.7.11.5-6); 



4. sexual dimorphism of P2 involving the loss of the inner distal 

 seta of enp-3 in the male; this seta is generally reduced in length 

 in other harpacticid genera such as Harpacticus, Tigriopus and 

 Paratigriopus but is completely absent in Zausodes sensu lato 

 and Perissocope. 



With the recent description of P. biarticulatus by Watkins (1987) 

 the absence of the inner seta on P2-P4 exp-1 can no longer be 

 regarded as a synapomorphy linking Perissocope and Zausodes. 

 The adhesive mucus strings produced by the caudal rami and the 

 associated glands were first described for Z. sextus and Z. septimus 

 by Lang (1965) and subsequently also reported for species of 

 Perissocope by Watkins ( 1 987). This character is not unique to these 

 two genera since a similar mucus apparatus has also been recorded 

 in other representatives of the Harpacticidae (Watkins, 1987) and 

 even outside this family (Huys, 1990). 



Although the Zaus-Zausopsis clade is undoubtedly monophyletic, 

 recognizing it as a distinct subfamily Zausodinae would relegate the 

 Harpacticinae to a taxon of paraphyletic status. We recommend 

 therefore to abandon Lang's (1944, 1948) subfamilial classification 

 until a comprehensive phylogenetic analysis of the family is com- 

 pleted. 



Morphological characters 



(1) Segmentation 9 antennule 



The female antennule is primitively 9-segmented in the Harpacticidae 

 with segments 7 and 8 representing ancestral segments XXIV and 

 XXV, respectively. The homology of these segments is established 

 by their posterior setae (Huys & Boxshall, 1991). This ancestral 

 condition is found in the genera Harpacticus, Zaus, Discoharp- 

 acticus, Tigriopus and Paratigriopus. Within the former Zausodes 

 complex the number of antennulary segments ranges between 6 and 

 8. The 8-segmented state is derived by fusion of segments 7 and 8, 

 forming a double segment in Z. arenicolus, Z. septimus, A. 

 biarticulatus and the two species of Mucropedia. The origin of this 

 compound segment is unequivocally established by the presence of 



2 posterior setae. Comparison of ontogenetic studies of harpacticid 

 genera possessing 9-segmented antennules such as Tigriopus (Ito, 

 1970) and Harpacticus (Ito, 1971, 1976; Ito & Fukuchi, 1978) 

 indicates that the double segment is not the result of a failure in the 

 separation of segments 7 and 8 at an earlier stage in ontogeny since 

 both these segments are already expressed at copepodid I. The 

 double segment is also found in all other Zausodes species (Table 1 ) 

 in which the antennule is only 7- or 6-segmented. It is regarded here 

 as a synapomorphy linking Perissocope and the Zausodes complex. 

 A further derived state is found in the 3 Brazilian species (Jakobi, 

 1954), N. sextus, N. schulenbergeri and N. areolatus in which a 

 triple segment is formed by incorporation of segment 6 into the 

 double segment, producing a 7-segmented (or 6-segmented in N. 

 areolatus) antennule. This condition has independently evolved in 

 the genus Perissocope (Wells, 1968). Our study has revealed a 6- 

 segmented antennule in N. areolatus which represents an 

 autapomorphy for this species. It has originated through fusion of 

 segment 5 to the aesthetasc-bearing segment 4. 



(2) Proximal elements 9 antennule 



The armature elements on the 9 antennule are typically setiform in 

 the great majority of the genera in the Harpacticidae. In some 

 species of Zausodes sensu lato particular elements on the proximal 

 segments are modified into stout, rigid spines which typically bear a 

 subapical flagellum (Figs 8A; 14A). The position and number of 

 these spines is identical in all species for which they have been 

 recorded, i.e. two on segment 3 and one on segments 4 and 5 each. 

 Two spines are found on segment 4 in N. areolatus as a result of 

 secondary segmental fusion. 



(3) Distal elements 9 antennule 



Some species of Zausodes sensu lato possess two large, conspicuous 

 spines on segment 6 (or the homologous portion of segment 5 in the 

 6-segmented antennule of N. areolatus). These spines are typically 

 unilaterally pinnate or pectinate (Figs 8A; 14A) and easy to discern 

 without dissection. They are not found on the male antennules. 



(4) Setal ornamentation 9 antennule 



Species of Perissocope and Zausodes sensu lato typically have 

 antennulary setae which lack any form of ornamentation. Outgroup 

 comparison with other harpacticid genera such as Zaus (Ito, 1980) 

 and Harpacticus (e.g. Ito, 1976) suggests that this is the ancestral 

 condition. In the type species Z arenicolus (Fig. 2B) and Z septimus 

 (Lang, 1965; Mielke, 1990) the four proximal segments of 

 the 9 antennule bear pinnate setae, the plumosity being much more 

 expressed in the latter. This modification is regarded here as 

 apomorphic. 



(5) Segmentation antennary exopod 



Within the Harpacticidae the antennary exopod is 3-segmented only 

 in Tigriopus and some species of Perissocope. Comparison of 

 setation patterns indicates that the 2-segmented condition is derived 

 by fusion of the middle and distal exopod segments. This segmenta- 

 tion is found in most harpacticid genera such as Harpacticus, Zaus, 

 Zausopsis and Harpacticella, and in three species of the former 

 Zausodes complex {biarticulatus, kirstenae, cookorum). All other 

 Zausodes species show the further derived 1 -segmented state (Table 

 1), being the most reduced condition within the family. 



(6) Armature antennary exopod 



The maximum setation is found in Harpacticus, Zaus and Zausopsis 

 which possess 2 lateral setae on exp-1 and 2 lateral plus 2 apical 



