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



rite (5 spines and process) occurs in Crassarietellus , Campan- 

 eria, Paraugaptiloides, Arietellus, Paramisophria, 

 Sarsarietellus and Pilarella. In Sarsarietellus the outer proxi- 

 mal spine is incompletely fused to the arthrite, while in the 

 other six genera the fusion is complete enough to form a 

 process. Both Paraugaptilus (5 spines) and Scutogerulus (4 

 spines and process) show more advanced states, and the 

 reduced element may be the inner proximal spine in both 

 genera. Metacalanus exhibits the most apomorphic state, in 

 the number of elements (0-2 setiform spines), and the 

 elements are not so strongly chitinized as in other genera. 



On the coxal endite a single seta is present in all the genera 

 except for Paraugaptilus. The relative length and the orna- 

 mentation of the seta are variable within polytypic genera. 

 The number of setae on the coxal epipodite varies in ari- 

 etellids. The maximum number (8 setae) is retained in 

 Paraugaptiloides , Arietellus, Paraugaptilus and Sarsarietellus , 

 whereas there are 6 in Crassarietellus and Campaneria, 5 in 

 Metacalanus, Scutogerulus and Pilarella. A vestigial basal 

 seta is present in Crassarietellus, Campaneria, Paraugapti- 

 loides, Paramisophria and Sarsarietellus, but absent in Ari- 

 etellus, Metacalanus, Paraugaptilus and Pilarella. The 

 position of this seta indicates that it probably represents the 

 second basal endite. 



The endopod is variously modified. The most plesiomor- 

 phic state, 1-segmented with 3 setae, is found in several 

 species of Paramisophria. A 1-segmented endopod with 2 

 setae is present in Crassarietellus, Campaneria, Paraugapti- 

 loides, Arietellus, Sarsarietellus and Pilarella; a 1-segmented 

 endopod with a single seta in Arietellus, Metacalanus and 

 Scutogerulus. Species of Arietellus and Metacalanus, espe- 

 cially the former, exhibit a variety of transformed states in the 

 endopod. The most apomorphic state in these 2 genera is 

 complete incorporation into the basis. Several species of 

 Arietellus display an intermediate state with the endopod 

 represented by a rudimentary, unarmed knob, almost fused 

 to the basis. In Paraugaptilus the endopod is completely 

 incorporated into the basis. 



10. Maxilla. The armature elements on the first and second 

 praecoxal endite, and the ornamentation on the basal and 

 endopodal setae are unique to each genus. On the first 

 praecoxal endite the most primitive state (2 setae and a 

 vestigial element) is retained in Crassarietellus, Campaneria, 

 Paraugaptiloides, Sarsarietellus, Paramisophria (only P. gise- 

 lae) and Pilarella. Arietellus, Metacalanus, Paraugaptilus and 

 Scutogerulus share the more apomorphic state (1 seta and a 

 vestigial element). In all these genera it is the outer seta on 

 the endite of the more plesiomorphic genera that is absent 

 and the inner one that remains, based on the position of the 

 setae on the endite. 



On the second praecoxal endite, 2 setae are present in 

 Crassarietellus, Campaneria, Paraugaptiloides, Arietellus, 

 Paramisophria, Metacalanus, Sarsarietellus and Pilarella, and 

 a single seta in Paraugaptilus and Scutogerulus. All genera 

 exhibit 2 setae on the first and second coxal endites. The 

 basal spine is variously ornamented in all genera except for 

 Paramisophria whose spine is bare. In Campaneria (Fig. 

 10G), Paraugaptiloides (Fig. 11F), Arietellus (Figs 

 13I,18F,G) and Sarsarietellus (Fig. 36G), the basal spine is 

 relatively elongate, ornamented with 2 rows of fine, long 

 spinules densely distributed along the entire length except for 

 the bare terminal part. Crassarietellus (Figs 5B,8D) also 

 carries a long basal spine with 2 rows of relatively thick 

 spinules distributed about at midlength. In Paraugaptilus 



(Fig. 29D) and Scutogerulus (Fig. 34D), the spinules are 

 minute and sparsely distributed. Metacalanus (Fig. 211) bears 

 a basal spine unique within arietellids; the spine is relatively 

 short, with 2 rows of minute, rigid spinules at midlength. In 

 Pilarella the basal spine is elongate with a single row of 

 spinules at midlength. 



The ornamentation on the endopodal setae is also charac- 

 teristic of each genus. In Crassarietellus, Campaneria, 

 Paraugaptiloides, Paramisophria, Metacalanus, Sarsarietellus 

 and Pilarella, the inner margin of these setae is furnished with 

 a row of slender, simple spinules (see Fig. 11G), whereas in 

 Arietellus, Paraugaptilus and Scutogerulus the ornamentation 

 is variable. Arietellus develops a lobate structure basally on 

 each spinule (Fig. 15B,C), while both Paraugaptilus (Fig. 

 27G) and Scutogerulus (Fig. 34F) carry a row of triangular 

 spinules along the inner margin of each seta. In arietellids 

 such setal ornamentation on the maxilla is also found on the 

 well-developed setae of the terminal endopod segments of 

 the maxilliped. Bradford (1969) referred to the setal orna- 

 mentation on the maxilla and maxilliped of Scutogerulus as 

 'shield-shaped appendages' in her definition of the genus. 



11. Maxilliped. Variation in arietellids can be found in the 

 armature on the fourth to sixth endopodal segments. The 

 innermost seta on the fourth and fifth segments is relatively 

 well-developed in all the genera except for Arietellus, in 

 which it is reduced to a vestigial element or is completely 

 absent. In Crassarietellus (Figs 6B,C,8E), Metacalanus (Fig. 

 26A,B), Paramisophria (Fig. 19D), Paraugaptilus (Fig. 27F) 

 and Pilarella, the innermost setae on the fourth and fifth 

 endopodal segments are of almost equal length; in Campan- 

 eria (Fig. 10H), Paraugaptiloides (Fig. 12B), Sarsarietellus 

 (Fig. 35C,D) and Scutogerulus (Fig. 34E) the innermost seta 

 on the fourth endopodal segment is longer than that on the 

 fifth. 



On the sixth endopodal segment the most plesiomorphic 

 state, with setae a and b developed, is retained in Crassari- 

 etellus (Fig. 5C), Paramisophria (Fig. 19E), Metacalanus 

 (Fig. 26C) and Pilarella (Fig. 37F); the most apomorphic 

 state, namely, reduced setae a and b is found in Arietellus 

 (Fig. 18H-K), Paraugaptilus (Fig. 27G) and Scutogerulus 

 (Fig. 34F). Campaneria (Fig. 101), Paraugaptiloides (Fig. 

 12B) and Sarsarietellus (Fig. 35E) show an intermediate 

 condition: only seta a is reduced and seta b is relatively long. 

 In Paraugaptilus only seta c is specialized, with its terminal 

 part heavily chitinized and serrated along the inner margin 

 (Figs 27G, 32E). Paraugaptiloides, however, shows no spe- 

 cialization of seta c (Fig.l2B). 



12. Leg 1. On the third exopodal segment two outer spines 

 are retained in Crassarietellus, Campaneria, Paraugaptiloides, 

 Arietellus, Paramisophria, Paraugaptilus and Sarsarietellus. 

 A single outer spine is found in Metacalanus, Scutogerulus 

 and Pilarella. Consideration of the relative position of the 

 spines suggests that it is the proximal spine that is lost in these 

 three genera. 



13. Legs 2 and 3. All genera and species, except for the 

 cave-dwelling Paramisophria galapagensis , retained the maxi- 

 mum setation of the endopods of legs 2 and 3: seta and spine 

 formula 0-l;0-2;2,2,4. In P. galapagensis the seta and spine 

 formula of the endopod is 0-l;0-2;2,2,3 (Ohtsuka et al., 

 1993a). This represents the most apomorphic state known in 

 arietellids. 



14. Leg 4. An inner coxal seta or a vestigial element is 

 present only in Paraugaptiloides, Paraugaptilus and Pilarella. 

 It is absent in the other genera, although a fourth copepodid 



