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



contrast A. simplex lacks all these characteristics (see Sars, 

 1924, plates 118, 120). Paramisophria species typically have a 

 pair of pointed dorsolateral and rounded or prominent vent- 

 rolateral processes on the last prosomal somite (e.g., Sars, 

 1903; Fosshagen, 1968; Campaner, 1977; McKinnon & Kim- 

 merer, 1985; Ohtsuka, 1985; Ohtuska & Mitsuzumi, 1990). 

 Although some cave-living species of Paramisophria lack 

 such processes (Ohtsuka et al., 1993a), there is a cave-living 

 Paramisophria with processes in Bermuda (Fosshagen, per- 

 sonal communication). The genera Paraugaptilus and 

 Paraugaptiloides consistently exhibit a pair of dorsolateral 

 processes on the last prosomal somite and no cephalic projec- 

 tion (Sars, 1924; Gaudy, 1965; Deevey, 1973; Bradford, 

 1974). Sarsarietellus has weakly developed dorsolateral 

 and/or ventrolateral processes on the last prosomal somite 

 (Sars, 1924, 1925; Heinrich, 1993). Crassarietellus, Metacala- 

 nus, Scutogerulus , Pilarella and, possibly, Campaneria lack 

 dorsolateral processes on the last prosomal somite and a 

 cephalic projection (Bradford, 1969; Alvarez, 1985; present 

 study). 



2. Genital double-somite. The present study has revealed 

 an amazing variety of genital systems of arietellid females. 

 The hypothetical ancestral calanoid proposed by Huys & 

 Boxshall (1991) was characterized by paired genital apertures 

 located about in the middle of the genital double-somite. This 

 basic condition is displayed by the genera Crassarietellus (Figs 

 1D,E,2A), Scutogerulus (Fig. 33B,C) and Pilarella (Fig. 

 37A). The paired gonopores are ventrolateral^ located at 

 about the midlength of the genital double-somite, and the 

 paired copulatory pores are situated either posterior to the 

 gonopores or at the midlength of the somite. Scutogerulus 

 exhibits the most plesiomorphic state, similar to that of the 

 primitive family Pseudocyclopidae (see Huys & Boxshall, 

 1991, Fig. 2.2.32): the gonopore and the copulatory pore 

 share a common opening, with the copulatory pore located 

 on the innermost part of the common opening; the gonopore 

 is located in the outer part of the common opening. Although 

 Huys & Boxshall (1991) did not mention the location of 

 paired seminal receptacles of the ancestor, it is likely that 

 they lie ventrally just beneath the gonopores as proposed for 

 the ancestor of the Cyclopoida (see Huys & Boxshall, 1991, 

 Fig. 2.8.37). 



Fig. 38 schematically depicts possible evolutionary trends 

 in structure of the female genital system in the Arietellidae, 

 based on the relative positions of gonopores and copulatory 

 pores. Five major trends are recognizable: (A) fusion of 

 copulatory pores to form a single common pore and antero- 

 lateral migration of gonopores; (B) posterior migration of 

 both gonopores and copulatory pores; (C) anterolateral 

 migration of gonopores, and asymmetrical arrangement and 

 enlargement of copulatory pores; (D) lateral migration of 

 both gonopores and copulatory pores, and copulatory pore 

 covered by ventral flap; (E) lateral migration of both gono- 

 pores and copulatory pores, copulatory pore uncovered. The 

 first three trends (A-C) are accompanied by the formation of 

 a pair of genital opercula, each of which closes off a gonopore 

 and opens anteriorly with a posterior hinge. The gonopore is 

 separate from the copulatory pore in all except the last trend 

 (E). The first evolutionary trend (A) is exhibited in Parami- 

 sophria, Arietellus and Sarsarietellus. The copulatory ducts 

 are heavily chitinized in Arietellus and Sarsarietellus (see Figs 

 13B,16A-C) but not so in Paramisophria (Figs 19A,20A). In 

 addition, each copulatory duct is connected to a medial part 

 of the seminal receptacle, but not so anteriorly as in Arietellus 



and Sarsarietellus. Even within the genus Paramisophria, a 

 remarkable trend is exhibited. In P. japonica and P. reducta, 

 the copulatory pore is located ventro-medially, whereas in P. 

 platysoma, P. itoi and P. cluthae the pore is present on the 

 left side of the genital double-somite (Ohtsuka & Mitsuzumi, 

 1990; Huys & Boxshall, 199i; Ohtsuka et al., 1991, 1993b). 

 Alternatively, the copulatory pore can be located on the right 

 side as in P. giselae. These asymmetrical species are thought 

 to be more derived than P. japonica. 



In Arietellus the genital system is essentially the same as in 

 Paramisophria, but may be relatively more apomorphic in 

 having: (1) copulatory ducts much more heavily chitinized; 

 and (2) enlargement of the copulatory pore. In Sarsarietellus 

 the systems are basically similar to those of both Parami- 

 sophria and Arietellus, but are more closely related to Arietel- 

 lus in having the two previously mentioned apomorphic 

 states. 



The genus Metacalanus exhibits the second trend (B). 

 Primitively, M. species 2, M. inaequicornis (Campaner, 

 1984), M. acutioperculum (Ohtsuka, 1984), M. curvirostris 

 (Ohtsuka, 1985) and, possibly, M. aurivilli display paired 

 gonopores and copulatory pores which are located along the 

 posterior margin of the genital double-somite. The gonopores 

 are relatively large. The copulatory pore is clearly separate 

 from the gonopore (see Figs 23A,24A), and is located near 

 the anterior inner corner of the gonopore. The seminal 

 receptacles are located ventrally at almost the same level as 

 the gonopore, and each is connected via a short, chitinized 

 copulatory duct. M. species 1 shows a further derived state 

 since it completely lacks the genital system on the left side. 

 The right genital structure of this species is quite similar to 

 that of the right side of other Metacalanus species, but is 

 bounded by a chitinized flap along the outer lateral margin 

 and the copulatory pore is slightly oblong in shape compared 

 with the rounded pore of the other congeners (see Figs 

 23,24). 



The third trend (C) is exhibited by the genus Paraugaptilus. 

 The gonopores are almost symmetrically sited anteriorly (see 

 Figs 28A, 31A) while the copulatory pores are extremely 

 asymmetrical (see Fig. 31B). The right copulatory pore is 

 slit-like and situated in a large circular ventral depression; the 

 left pore is a large pore located posterior to the right. The left 

 copulatory duct is much longer than the right, although both 

 ducts are heavily chitinized. The seminal receptacles are 

 relatively small, bulbous, and located just posterior to the 

 gonopore; the right is better developed than the left (Fig. 

 27A,B). However, both genital systems are probably func- 

 tional because of the presence of well-developed muscles 

 which provide an opening-closing mechanism for the genital 

 operculum on both sides. In the recently established calanoid 

 family Hyperbionycidae (Ohtsuka et al., 1993b), only the left 

 genital system is functional; the right side lacks musculature 

 around the gonopore and is probably no longer functional. 

 Only two species of Paraugaptilus were available for the 

 present study but Gaudy's (1965) and Deevey's (1973) illus- 

 trations of the ventral surfaces of the female genital double- 

 somites of P. mozambicus and P. bermudensis suggest that 

 these species exhibit the same genital systems. 



The fourth (D) and fifth trends (E) are displayed by 

 Crassarietellus, and by Scutogerulus and Pilarella, respec- 

 tively. Both trends show primitive states of the female genital 

 system in the presence of paired and symmetrically arranged 

 gonopores, copulatory pores and seminal receptacles. How- 

 ever, both trends exhibit different variations of the plesio- 





