128 



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



Remarks. The present study revealed that Paraugaptilus 

 mohri Bjornberg, 1975 belongs to the genus Arietellus (see 

 below). Arietellus shows sexual dimorphism in the antenna 

 and mandibular palp, as described in Paraugaptilus by 

 Deevey (1973). However, no sexual dimorphism is exhibited 

 in the maxillule, the maxilla and the maxilliped. 



Ecological note. Species of the genus are pelagic and 

 distributed in deep water throughout the world's oceans 

 (Brodsky, 1950; Vervoort, 1965; Roe, 1972, unpublished 

 data; Campaner, 1984). 



Arietellus plumifer Sars, 1905 (Figs 13-15, 17A,18L) 



Material examined. 2 $ and cf . 



Body length. $ 5.88 mm (28 VI 1985), 6.24 mm (26 XI 

 1965); Cf 5.46 mm. 



Description. Female. Cephalosome separate from first pedi- 

 gerous somite. Genital double-somite (Figs 13A,B,14) as long 

 as wide, almost symmetrical, with pair of gonopores ventrolat- 

 erally and anterior to single ventromedial copulatory pore; 

 paired copulatory ducts chitinized, each running anteriorly to 

 connect with seminal receptacle near genital operculum; semi- 

 nal receptacle located lateromedialfy, half as long as double- 

 somite, produced posteriorly with rounded posterior tip, 

 tapering anteriorly; receptacle duct beneath copulatory duct, 

 opening near inner corner of genital operculum. 



Antennule symmetrical, 20-segmented; seventh (X) to 

 ninth (XII) segments and 11th (XIV) and 12th (XV) seg- 

 ments only partly fused. Fusion pattern and armature ele- 



ments as follows: I-IV-9 + 2 aesthetascs, V-2 + aesthetasc, 

 VI-2, VII-2 + aesthetasc, VIII-2, IX-2 + (small) aesthetasc, 

 X-2, XI-2 + aesthetasc; XII-2, XIII-2 + aesthetasc, XIV-2 

 + aesthetasc, XV-2 +aesthetasc, XVI-2 + aesthetasc, 

 XVII-2 + aesthetasc, XVIII-2 + aesthetasc, XIX-2 + 

 aesthetasc, XX-2 + aesthetasc, XXI-2 + aesthetasc,XXII-l, 

 XXIII-XXVIII-12 + 2 aesthetascs (Fig. 13C). First (I-IV) to 

 seventh segments fringed with long setules along posterior 

 margin. 



Antenna: first endopod segment without inner seta, second 

 segment with 2 short inner setae of unequal lengths (Fig. 

 15D) and 5 terminal setae and reduced setule terminally; 

 exopod indistinctly 7-segmented; setal formula 0,1,1,1,1,0,3. 

 Mandibular palp (Fig. 13E,F): endopod absent; first exopod 

 segment having relatively reduced seta, fifth segment carry- 

 ing normal seta and vestigial element. 



Maxillule: praecoxal arthrite (Fig. 13G) with 5 naked 

 spines, 1 short process and row of long setules; coxal endite 

 (Fig. 13G) carrying relatively long spinulose seta, fringed 

 with numerous long setules along distal margin; basal seta 

 lacking; endopod (Fig. 13G, indicated by arrowhead) rudi- 

 mentary, almost fused with basis, unarmed. Maxilla: first 

 praecoxal endite bearing thick naked seta and vestigial ele- 

 ment, second praecoxal endite having 2 spinulose setae (Fig. 

 13H); basal spine (Fig. 131) with 2 rows of minute spinules 

 along ventral margin. 



Maxilliped: sixth endopod segment (Fig. 15A.B) having 

 elongate seta d with row of stout spinules whose base 

 ornamented with lamellar projection (Fig. 15C), finely ser- 

 rated, medial-length seta c and reduced setae a and b. 



Fig. 14. Arietellus plumifer, female. SEM micrographs of genital double-somite of female. A, Genital double-somite, ventral view showing 

 large copulatory pore (indicated by an arrow), scale bar = 100 p.m; B, Right gonopore, scale bar = 30 urn; C, Copulatory pore, scale bar = 

 20 u.m. 



