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



Scutogerulus exhibit a more primitive state than genera found 

 in other habitats, with the exception of Sarsarietellus which, 

 however, may be a deep-water hyperbenthic species (Cam- 

 paner, 1984). In contrast, the shallow-water pelagic and 

 hyperbenthic genera Metacalanus, Paramisophria and 

 Pilarella independently exhibit relatively derived genital sys- 

 tems. The bathypelagic genera Arietellus and Paraugaptilus 

 have also independently developed a more apomorphic geni- 

 tal system than the deep-sea hyperbenthic genera. 



3. Caudal ramus. The caudal rami of almost all arietellids 

 are symmetrical. However, asymmetry of caudal rami is 

 exhibited in Scutogerulus, in which the left ramus is slightly 

 longer than the right (Bradford, 1969; present study, Fig. 

 33 A), and in Pilarella in which the left caudal ramus is slightly 

 larger than the right (present study). 



Except in Metacalanus the armature elements on the 

 caudal ramus are all retained. In all genera seta I is minute 

 and setae III— VII are developed to varying degrees. Seta II is 

 relatively minute or completely absent in Metacalanus , but 

 always present in the other genera. Arietellus pavoninus has 

 highly specialized caudal rami with densely plumose seta II 

 that is directed anteriorly (Sars, 1924, 1925). 



4. Rostrum. All arietellids have a well-developed rostrum 

 produced ventrally with a pair of filaments. Both sexes of 

 Metacalanus curvirostris have a rostrum that curves to the left 

 (Ohtsuka, 1985). 



5. Female antennule. The antennulary segmentation and 

 setation patterns of female arietellids are summarized in Fig. 

 39. Some genera show variability in segmentation and/or 

 setation. In particular, Metacalanus exhibits asymmetry in 

 both segmentation and armature (Fig. 22). The segmentation 

 and setation of Crassarietellus represent the most plesiomor- 

 phic state within the family, displaying both the maximum 

 segmentation and the greatest number of armature elements 

 as follows (Fig. 39A): separation of ancestral segment III 

 from IV; segments IV to XXI each with 2 setae and aes- 

 thetasc; segments X-XII separate; segments XIV and XV 

 separate; segments XXIII and XXIV separate. 



Ancestral segments I— III are fused in Crassarietellus (Fig. 

 39A), Scutogerulus (Fig. 39C), Sarsarietellus (Fig. 39B) and 

 Paramisophria (Fig. 39D), and segments I-IV in Arietellus 

 (Fig. 39E), Metacalanus (Fig. 39G), Paraugaptilus (Fig. 39F) 

 and Pilarella (Fig. 39H). Segments XXIII and XXIV are 

 separate in Crassarietellus , Paramisophria, Scutogerulus, Sar- 

 sarietellus, Metacalanus and Pilarella, and fused in Arietellus 

 and Paraugaptilus . The complete fusion of segments IX and 

 X is unique to Metacalanus. 



The loss of an aesthetasc on segment IV is found in seven 

 genera; that on segment II in Pilarella; that on segment VI in 

 Arietellus, Paraugaptilus, Metacalanus and Pilarella; those on 

 segments VIII and X in Paraugaptilus and Metacalanus; that 

 on segment XII in Arietellus and Paraugaptilus; those on 

 segments XXII and XXIII in Pilarella. One element on 

 segment XIII is reduced in Paraugaptilus and Metacalanus. 

 One seta on compound segment XXVI-XXVIII is reduced in 

 Arietellus and in Paraugaptilus similis. 



The presence of a duplicated aesthetasc at the extreme tip 

 of antennule of Paraugaptilus similis is interpreted here as an 

 individual abnormality. 



The right and left antennules are markedly asymmetrical in 

 length in the genera Paramisophria, Metacalanus and 

 Pilarella, which are mainly distributed near the sea bed. This 

 asymmetry has been related to the peculiar swimming behav- 

 iour of these genera at the sediment-water interface (see 



Ohtsuka & Mitsuzumi, 1990). The ornamentation of the right 

 and left antennules is slightly asymmetrical on the terminal 

 segments in the bathypelagic genus Paraugaptilus. 



6. Male left antennule. The antennulary segmentation and 

 setation patterns of male arietellids are summarized in Fig. 

 40. Ancestral segments II to IV are incompletely fused in 

 Campaneria (Fig. 40A) and completely fused in the other six 

 genera. Fusion of segments IX-X is unique to Metacalanus 

 (Fig. 40G), whereas complete separation of segment XXI 

 from XXII is found only in Campaneria. Each of ancestral 

 segments II and III carries 2 setae and an aesthetasc in 

 Crassarietellus (Fig. 40B), and 1 seta and an aesthetasc in the 

 other genera. In Arietellus aculeatus segments I to IV bear 1, 

 2, 2 and 2 aesthetascs, respectively. The presence of one 

 additional aesthetasc on each segment from II to IV seem to 

 be a secondary addition found in the males of many pelagic 

 calanoids (see Huys & Boxshall, 1991). Huys & Boxshall 

 (1991) speculated that duplication of aesthetascs in males is 

 an adaptation for the open pelagic environment. The oceanic 

 pelagic species A. aculeatus shows duplication of aesthetascs, 

 and neither shallow- nor deep-water hyperbenthic arietellids 

 have such duplication. However, no other pelagic species of 

 either Arietellus or Paraugaptilus has such duplication, and its 

 occurrence within a single species of a relatively derived 

 genus may indicate that the duplication of aesthetascs in A. 

 aculeatus arose independently. 



A seta on segment XV is modified, by loss of its proximal 

 articulation with the segment, into a process in Arietellus, 

 Paraugaptilus and Paraugaptiloid.es; a seta on segment XXII 

 is also modified into a process in Crassarietellus, Campaneria 

 and Metacalanus. Only in Paraugaptilus and Paraugaptiloid.es 

 does the compound segment XXIV-XXV carry a large 

 distally directed process (Figs 11B, 30E, 32F). From its 

 position, this process may be derived from a setation element 

 of segment XXIV, but we consider it more likely that it 

 represents an outgrowth of the segment. The loss of a seta on 

 the compound segment XXVI-XXVIII is found in Arietellus 

 and Paraugaptilus. The lack of a seta on segment XIII is 

 unique to Metacalanus. 



7. Antenna. The ancestral condition of the antennary 

 exopod of Copepoda is shown by Huys & Boxshall (1991): 

 the exopod consists of 10 separate segments; first to ninth 

 segments each bearing a single seta, the 10th segment with 3 

 setae (Fig. 41A). The segmentation and setation patterns of 

 the arietellid genera are schematically depicted in Fig. 

 41B-H. In all genera, ancestral exopodal segments I and II, V 

 and VI, VI and VII, and VII and VIII are either completely 

 separate or incompletely fused with a suture still visible. In all 

 genera, ancestral segments IV, V, VI and VII each carry 1 

 seta while segments I, II, III and IX are unarmed. Segment X 

 carries 3 setae except in Paraugaptilus (Fig. 41G,H). A seta is 

 present on segment VIII in Crassarietellus (Fig. 41B), Cam- 

 paneria (Fig. 41D), Paraugaptiloides (Fig. 41D), Parami- 

 sophria (Fig. 41D), Metacalanus (Fig. 41E), Sarsarietellus 

 (Fig. 41D), Scutogerulus (Fig. 41D) and Pilarella (Fig. 41D), 

 but absent in Arietellus (Fig. 41F) and female Paraugaptilus 

 (Fig. 41H). Complete fusion of ancestral segments II-IV 

 occurs in Campaneria, Paraugaptiloides, Arietellus, Parami- 

 sophria, Metacalanus, Paraugaptilus, Sarsarietellus, Scu- 

 togerulus and Pilarella. Complete fusion of segments VIII-IX 

 occurs in Arietellus, Metacalanus and female Paraugaptilus. 

 The most advanced state is found in female Paraugaptilus 

 (Fig. 41H): ancestral segments VIII to X are completely 

 fused to form an unarmed, bulbous compound segment in P. 



