130 



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



Leg 1: third exopod segment with 2 subterminal serrate 

 spines. 



Leg 5 (Fig. 17A): coxae incompletely fused with intercoxal 

 sclerite; right basal seta extremely elongate; endopod repre- 

 sented by knob with 2 plumose setae; exopod incompletely 

 fused with basis, 1-segmented, carrying 1 terminal spine. 



Male. Left antennule (Fig. 15E) distinctly 19-segmented; 

 8th to 11th segments only partly fused near posterior margin; 

 fusion pattern and armature elements as follows: I-IV-7 + 2 

 aesthetascs (1-3 + aesthetasc, II— 1 + aesthetasc, III— 1 + 

 aesthetasc, IV-2 + aesthetasc), V-2 + aesthetasc, VI-2 + 

 aesthetasc, VII-2 + aesthetasc, VIII-2 + aesthetasc, IX-2 + 

 aesthetasc, X-l + aesthetasc + process, XI-2 + aesthetasc, 

 XII-1 + aesthetasc + process, XIII-1 + aesthetasc + pro- 

 cess, XIV-1 + 2 aesthetascs + process, XV-1 + aesthetasc + 

 process, XVI-2 + aesthetasc, XVII-2 + aesthetasc, XVIII-2 

 + aesthetasc, XIX-1 + aesthetasc + 2 processes, XX-1 + 

 aesthetasc + process, XXI-XXIII-2 + aesthetasc + 2 pro- 

 cesses (XXI-aesthetasc + 2 processes, XXII-1, XXIII-1), 

 XXIV-XXVIII-11 + 2 aesthetascs (XXI V-l + 1, XXV-1 + 

 1 + aesthetasc, XXVI-XXVIII-7 + aesthetasc); no suture 

 visible between segments XXV and XXVI. First (I-IV) to 

 sixth (IX) segments fringed with long setules along posterior 

 margin. 



Antenna: second endopod segment (Fig. 15F) with 1 short 

 and 1 long seta medially and 5 setae and 1 vestigial setule 

 terminally. Mandibular palp (Fig. 15G): first exopod segment 

 with well-developed seta. 



Leg 5 (Fig. 18L): both coxae fused to intercoxal sclerite to 

 form common plate, right coxa almost fused with basis, left 

 coxa completely separate from basis. Right leg: basal seta 

 considerably elongate; endopod 1-segmented, spatulate; exo- 

 pod indistinctly 3-segmented, first segment with 1 spine on 

 outer corner, second incompletely fused with third, furnished 

 with triangular process and 2 tufts of fine setules on inner 

 corner and 1 spine on outer corner, third segment spatulate, 

 with subterminal outer setule and terminal vestigial element. 

 Left leg: endopod indistinctly 2-segmented, first and second 

 segments unarmed; exopod indistinctly 3-segmented, first 

 segment with 1 spine on outer corner, second segment 

 incompletely fused with third, expanded inwards, bearing 1 

 subterminal outer spine, third segment small, having minute 

 spinule and 2 spines almost fused basally with segment, 

 terminal one bifid at tip. 



Arietellus mohri (Bjornberg, 1975), new combination 

 (Figs 16A, 17C, 18A,B,F,H) 



Material examined. $ , U.S. National Museum, reference 

 number USNM 150095. 



Body length. 6.40 mm (after Bjornberg, 1975) 



Description. Female. Cephalosome separate from first 

 pedigerous somite. Genital double-somite (Fig. 16A) as long 

 as wide, with anterior pair of gonopores located ventrolater- 

 al^ anterior to single ventromedial copulatory pore as in A. 

 plumifer; copulatory ducts much more chitinized and wider 

 than in A. plumifer, slightly asymmetrical, left duct divergent 

 into blind tubule near left genital operculum; seminal recep- 

 tacle the same shape as in A. plumifer. 



Right antennule (left antennule missing distal segments) 

 with fusion pattern and armature as A. plumifer except for 

 missing elements. Antenna: first endopod segment unarmed, 

 second segment with 2 inner setae of unequal length medially 



and 5 setae and 1 vestigial setule terminally; exopod 

 7-segmented, setal formula: 0,1,1,1,1,0,3. Mandibular palp 

 (Fig. 18A,B): endopod absent; exopod 5-segmented, first to 

 fourth segments each with 1 seta, first segment with well- 

 developed seta, fifth segment with 1 long seta and vestigial 

 seta. 



Maxillule: praecoxal arthrite with 5 naked spines and 1 

 bare process; coxal endite with 1 naked, thick seta terminally, 

 fringed with long setules along ventral margin; coxal epi- 

 podite with 8 setae; endopod absent. Maxilla: first praecoxal 

 endite with long, bare seta and 1 vestigial element; basal 

 spine (Fig. 18F) with 2 rows of spinules along ventromedial 

 margin. Maxilliped: fourth and fifth endopod segments each 

 with only 2 well developed setae and lacking innermost seta, 

 sixth segment (Fig. 18H) with vestigial seta a and short seta b. 



Leg 1: basis with inner and, possibly, outer (scar present on 

 outer margin) setae; third exopod segment with 2 lateral 

 bipinnate spines. Leg 4, possibly, with 1 basal outer seta (scar 

 present). Leg 5 (Fig. 17C): coxa and intercoxal sclerite almost 

 fused, but suture line visible on left side; basis completely 

 fused with coxa. Right leg: outer basal seta more elongate 

 than left one; endopod represented by small knob with 

 vestigial element at tip; exopod almost fused with basis, but 

 suture visible only on anterior surface, unarmed, round. Left 

 leg: basis with concavity on inner margin; outer basal seta 

 thick, plumose; endopod reduced to low prominence with 

 spinulose seta terminally; exopod almost completely fused 

 with basis, unarmed, round. 



Remarks. Bjornberg (1975) assigned one female of a new 

 species collected from the southeastern Pacific (depths: 

 1932-3142 m) to the genus Paraugaptilus, probably because 

 of the remarkably reduced fifth legs. The present 

 re-examination revealed that it belongs to Arietellus not to 

 Paraugaptilus , on the basis of the following characters: (1) 

 the genital double-somite with single copulatory pore ventro- 

 medially; (2) the first, sixth and 10th antennulary segments 

 carrying 2, 1 and 1 aesthetascs, respectively; (3) the antennu- 

 lary segment XXVI-XXVIII with 7 setae and 1 aesthetasc; 

 (4) the coxal endite of maxillule bearing 1 relatively well 

 developed seta and fringed with long setules along ventral 

 margin; (5) the second praecoxal endite of maxilla having 2 

 setae; (6) the endopodal setae of maxilla carrying sharp 

 spinules with lamellar structure basally; (7) the fourth and 

 fifth endopodal segments of maxilliped lacking innermost 

 seta; (8) leg 4 without inner coxal seta; (9) leg 5 with distinct 

 distal lobe derived from exopod; (10) the right basal seta of 

 leg 5 considerably elongate. 



Although Bjornberg (1975) described the species in rela- 

 tively great detail, the present re-examination of the holotype 

 revealed that her description included several misinterpreta- 

 tions, particularly in the mouthparts and legs. These are 

 amended in the present description. 



Arietellus aculeatus (T. Scott, 1894) (Figs 

 16F,G,18D,E,0) 



Material examined. 9 ar >d 2 Cf Cf. 



Body length. °- 4.62 mm; o" 3.77, 3.79 mm. 



Description. Female. Cephalosome separate from first 

 pedigerous somite. Left antennule similar to that of female 

 A. plumifer except for following points: segments VIII and X 

 each with minute aesthetasc; segment XIV carrying 2 setae 



