PHYLOGENY OF ARIETELLID COPEPODS 



161 







A 



w 



-va:::. 

 c 



" ;: W 



i—UP. 



M2 



! seminal receptacle 

 :: copulatory duct 

 receptacle duct 



Fig. 38. Evolutionary trends in the structures of the female genital systems of the arietellid genera. A, Fusion of copulatory pores to form 

 single pore, and anterolateral migration of both gonopores; B, Posterior migration of both gonopores and copulatory pores, and separation 

 of. copulatory pore from gonopore; C, Anterolateral migration of gonopores, and separation of copulatory pore from gonopore and their 

 asymmetrical arrangement and enlargement; D, Lateral migration of both gonopores and copulatory pores, and separation of copulatory 

 pore from gonopore; E, Lateral migration of both gonopores and copulatory pores. Pg: Paramisophria giselae; Pj: Paramisophria japonica; 

 Pc: Paramisophria cluthae; Sa: Sarsarietellus abyssalis; Ap: Arietellus plumifer; Ml: Metacalanus species 1; M2: Metacalanus sp. 2; Ps: 

 Paraugaptilus similis; Ch: Crassarietellus huysi; Sp: Scutogerulus pelophilus. g: gonopore; c: copulatory pore. 



morphic genital system. In Scutogerulus and Pilarella each 

 copulatory pore shares a common opening with the gonop- 

 ore, whereas in Crassarietellus each copulatory pore is sepa- 

 rate from the gonopore and located beneath the ventral flap. 

 The latter is probably more derived since the copulatory 

 pores are separate from the gonopores. In both trends, the 

 copulatory duct is relatively short and the seminal receptacle 

 is a simple spherical shape. 



In the specimens of Crassarietellus examined, a pair of 

 fertilization tubes from the spermatophore remnant (Figs 

 2A,3) was still connected to the copulatory pores. In this 

 genus each copulatory pore seems to be relatively large and 

 opens onto the inner surface of the ventral flap. The end of 



the fertilization tube terminates in a mass of brownish opaque 

 material (see Fig. IE, dotted) positioned where the copula- 

 tory pore opens. The gonopore is not covered by a genital 

 operculum, as in other arietellid genera (Fig. 2C,D). An 

 exposed gonopore, as in Crassarietellus, is also found in the 

 deep-sea hyperbenthic calanoid family Hyperbionycidae 

 (Ohtsuka et al., 1993b). Owing to the complete absence of 

 armature elements on leg 6 in the Calanoida, it is unknown 

 whether the absence of a genital operculum in Crassarietellus 

 represents a secondary loss or a more plesiomorphic state 

 than other arietellids. Radiation of the genital systems of 

 arietellids can be related to their different habitats. Gener- 

 ally, deep-sea hyperbenthic genera such as Crassarietellus and 



