158 



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



dorsalmost of which tricuspid; endopod rudimentary, 

 1-segmented with 2 setae; seta on first exopod segment not 

 reduced; outer seta on fifth segment relatively long. Maxil- 

 lule; praecoxal arthrite with 6 elements (5 setae and 1 

 process); coxal epipodite with 5 setae; coxal endite with 1 

 long seta; basal seta absent; endopod bearing 2 setae. Max- 

 illa: first praecoxal endite with 2 setae and vestigial element, 

 second praecoxal endite with 2 setae; basal spine with 2 rows 

 of spinules. Setal formula of endopod segment of maxilliped 

 1,4,4,4,3,3,4; setae a and b on sixth endopod segment rela- 

 tively well developed. 



Leg 1 with 1 outer spine on third exopod segment. Leg 4 

 with inner seta on coxa. Leg 5: coxae separate from reduced 

 intercoxal sclerite; endopod represented by 1 seta; exopod 

 and basis separate. Exopod 1-segmented bearing 1 short 

 spine on outer margin and 1 short and 1 long spine terminally. 



Type species. Pilarella longicornis Alvarez, 1985 (mono- 

 typic). 



Remarks. As Alvarez (1985) has already pointed out, the 

 genus Pilarella is very similar to Metacalanus, but can be 

 distinguished from the latter in the structures of antennules, 

 maxillule and caudal rami. The present study revealed that 

 the genital double-somite of Pilarella resembles that of Scu- 

 togerulus. A short supplementary description follows, provid- 

 ing details of setation and genital structure that were not 

 apparent in the original description (Alvarez, 1985). 



Ecological notes. The species was collected from near- 

 bottom at a depth of 135 m (Alvarez, 1985), and is, presum- 

 ably, a shallow-water hyperbenthic species. 



Pilarella longicornis Alvarez, 1985 (Fig. 37) 



Material examined. 3$$, paratypes, Copepod collection 

 of Departmenta de Zoologia, Instituto de Biociencias, Uni- 

 versidade de Sao Paulo, Brasil, No. 186. 



Body length. 1.53 to 1.73 mm (after Alvarez, 1985). 



Description. Genital double-somite (Fig. 37A) wider than 

 long; genital system symmetrical; genital aperture slit-like, 

 located just posterior to mid-length; large circular gonopores 

 present at outermost extremity of genital aperture and small 

 copulatory pore at innermost extremity; copulatory and 

 receptacle ducts short; seminal receptacle relatively small, 

 located medial to gonopore. Caudal rami slightly asymmetri- 

 cal, with right ramus narrower and just shorter than left, with 

 setae II and III relatively long. 



Antennules (see Fig. 39 ) asymmetrical, left longer than 

 right and reaching to end of caudal rami; both antennules 

 21-segmented; posterior proximal margin lacking long set- 

 ules. Fusion pattern and armature as follows: I-IV-9 + 2 

 aesthetascs, V-2 + aesthetasc, VI-2, VII-2 + aesthetasc, 

 VIII-2 + aesthetasc, IX-2 + aesthetasc, X-2 + aesthetasc, 

 XI-2 + aesthetasc, XII-2 + aesthetasc, XIII-2 + aesthetasc, 

 XI V-2 + aesthetasc, XV-2 + aesthetasc, XVI-2 + aes- 

 thetasc, X VII-2 + aesthetasc, XVIII-2 + aesthetasc, XIX-2 

 + aesthetasc, XX-2 + aesthetasc, XXI-2 + aesthetasc, 

 XXII-1, XXIII-1, XXIV-XXVIII-12 + 2 aesthetascs. 



Antenna: second endopod segment (Fig. 37B) with 3 setae 

 of unequal lengths at midlength and 5 setae terminally; 

 exopod indistinctly 7-segmented. Maxillule: praecoxal arth- 

 rite (Fig. 37C) with 6 elements (5 setae and 1 process); coxal 

 epipodite with 5 setae; endopod bearing 2 setae of unequal 



lengths (Fig. 37D). Maxilla: first praecoxal endite with 2 

 setae and vestigial element (Fig. 37E), second praecoxal 

 endite with 2 spinulose setae; basal spine with 2 rows of 

 spinules. Maxilliped: setae a and b on sixth endopod segment 

 (Fig. 37F) relatively well developed. 



Leg 1 with 1 outer spine on third exopod segment. Leg 4 

 with short inner seta on coxa. Leg 5: coxae separate from 

 small intercoxal sclerite; endopod represented by 1 relatively 

 long seta; exopod and basis separate; exopod 1-segmented 

 bearing 1 short spine on outer middle margin and 1 short 

 outer and 1 long inner spine terminally. 



DISCUSSION 



Ancestral states and character transformation 



All genera of the family Arietellidae except Rhapidophorus 

 are described in detail and their characters are discussed prior 

 to analysis of the phylogenetic relationships between the 

 genera. Within a single genus various states can be observed 

 in appendage segmentation and setation patterns. For 

 example, Metacalanus species show a variety of character 

 states in the antennules (Fig. 22) and fifth legs (Fig. 

 26E,F,H). In such a case, the most plesiomorphic state is 

 selected as the ancestral state for the genus, using the 

 principle of deduction of ancestral states proposed by Huys & 

 Boxshall (1991). Fig. 22 schematically depicts the segmenta- 

 tion and setation of right and left female antennules of 2 new 

 species of Metacalanus collected from Okinawa, South Japan. 

 Asymmetry in segmentation and setation is exhibited in both 

 species. The fewest segmental fusions and the greatest num- 

 ber of armature elements on each segment are combined 

 from both antennules of these two species in order to arrive at 

 a hypothetical ancestral condition. The hypothetical anten- 

 nule of ancestral Metacalanus so constructed is used for 

 comparison with antennules of other arietellid genera. 



In the antenna and mandibular palp of Arietellus and 

 Paraugaptilus , which show sexual dimorphism, the more 

 plesiomorphic state from either sex is selected as the generic 

 character state. By reference to the ancestral character states 

 for Calanoida (Huys & Boxshall, 1991) the evolutionary 

 trends within the family are traced. 



1. Body plan. The most primitive condition in the family 

 can be seen in Crassarietellus and Sarsarietellus . The body is 

 symmetrical with complete separation between the cephalo- 

 some and the first pedigerous somite; there is no projection at 

 the tip of the cephalosome, no strong dorso- and ventrolat- 

 eral processes on the last prosomal somite, and no specializa- 

 tion of the caudal ramus. 



Asymmetry in the body, except for female genital double- 

 somites, can be seen in the ventrolateral processes on the last 

 prosomal somite in Arietellus giesbrechti (Sars, 1924, 1925), 

 A. mohri (Bjornberg, 1975), and A. sp.; in the ventrolateral 

 corners of the second and third pedigerous somites in Parami- 

 sophria giselae (Campaner, 1977); and in the prosome of 

 Paramisophria platysoma (Ohtsuka & Mitsuzumi, 1990). 

 These are more apomorphic states compared with congeners 

 which have symmetrical counterparts. The asymmetrical 

 prosome of P. platysoma appears to result from its specialized 

 adaptation to the hyperbenthic zone (Ohtsuka & Mitsuzumi, 

 1990). 



The cephalosome is separate from the first pedigerous 



