138 



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



Remarks. The fusion pattern of the antennulary segments is 

 slightly different from the male of P. japonica in which 

 segments XXI and XXII are incompletely fused whereas 

 segments XXIII and XXIV are separate. 



Genus Metacalanus Cleve, 1901 



Diagnosis (emended). Female. Body compact, small, mea- 

 suring approximately 1 mm in body length. Prosome oval in 

 dorsal view, not produced frontally; cephalosome and first 

 pedigerous somite separate or weakly fused; posterior cor- 

 ners of last prosomal somite produced to form ventrolateral 

 lobe, without dorsolateral processes; urosome short, less than 

 one-third length of prosome. Genital double-somite wider 

 than long, with ventrolateral pair of gonopores or only right 

 gonopore (left reduced) located posteriorly; paired copula- 

 tory pores small, located near inner corner of genital aperture 

 (in the case of reduction of left gonopore, only right copula- 

 tory pore present); anal operculum either developed, triangu- 

 lar or not. Caudal rami symmetrical, longer than wide, with 

 seta II reduced or completely lacking; seta III relatively 

 small. 



Antennules asymmetrical, left longer than right and reach- 

 ing to end of prosome, different in fusion pattern and 

 armature; indistinctly 18- or 20-segmented in right antennule, 

 16- or 18-segmented in left; posterior proximal margin lack- 

 ing long setules; segments I-IV up to VI; segments IX and X 

 fused; segments XII to XIV fused in left; segments II, VII 

 and IX with 1 or 2 setae; segment XIII with 1 seta; segments 

 II, IV, VI, VIII and X lacking aesthetasc; segments V, XII 

 and XIII with or without aesthetasc; compound segment 

 XXVI-XXVIII with 8 setae and aesthetasc. Antenna: first 

 endopod segment with 1 inner seta, second with 2 setae 

 medially and 5 setae terminally; exopod indistinctly 

 7-segmented. Mandibular gnathobase lacking tuft of setules; 

 4 teeth on cutting edge, dorsalmost of which trifid at tip. 

 Mandibular palp: endopod almost fused to basis, represented 

 by small knob with 1 or 2 setae terminally; seta on first 

 exopod segment not reduced; outer seta on fifth exopod 

 segment relatively long. Maxillule: praecoxal arthrite with 

 0-2 spines; coxal endite with or without 1 short seta; coxal 

 epipodite with 5 setae; endopod absent or 1-segmented, 

 bulbous with 1 seta. Maxilla: first praecoxal endite with 1 seta 

 and 1 rudimentary element; basal spine with 2 rows of minute 

 spinules proximally; endopodal setae with row of spinules 

 along inner margin. Maxilliped: setal formula on first to sixth 

 endopod segments 1,4,4,3,3,4; innermost seta on fourth and 

 fifth endopod segments not reduced; only distalmost seta on 

 these segments well-chitinized and long; setae a and b on 

 sixth endopod segment not reduced. 



Third exopod segment of leg 1 with single outer spine. Leg 

 5: coxae separate from intercoxal sclerite; endopod repre- 

 sented by 1 seta or completely absent; exopod and basis fused 

 or separate; exopod either 1-segmented, with 1-3 spines or 

 represented by small knob bearing 1 seta. 



Male. Body as in female, measuring less than 1 mm in body 

 length. Left antennule 16-segmented; segments I-IV, IX-X 

 and XII-XIV fused; segment XIII without seta; segment XXI 

 separate from XXII. Leg 5: coxae and intercoxal sclerite 

 fused; basis separate from coxa; endopod absent; exopod 

 3-segmented, third segment with large seta almost fused with 

 segment. 



Type species. Metacalanus aurivilli Cleve, 1901 (= Scottula 



ambariakae Binet and Dessier, 1968) (monotypic). 



Other species. M. inaequicornis (Sars, 1902); M. acutioper- 

 culum Ohtsuka, 1984; M. curvirostris Ohtsuka, 1985; M. 

 species 1 and 2 from Okinawa. 



Remarks. Metacalanus was recognized as a senior synonym 

 of Scottula Sars, 1902 by Campaner (1984). 



Ecological note. M. aurivilli seems to be epipelagic in 

 subtropical waters in the Indo-West Pacific (cf. Greenwood, 

 1978). Other species are hyperbenthic in shallow waters in 

 temperate and subtropical regions (cf. Sars, 1903; Ohtsuka, 

 1984, 1985), or are marine cave-dwellers (Ohtsuka et al., 

 1993a). 



Metacalanus species 1 (Figs 21B-I,23,25A,26A-G) 



Material examined. 4 9$ and cf. 



Body length. $ 0.81, 0.83, 0.83, 0.84 mm; cf 0.77 mm. 



Description. Female. Cephalosome only partly fused with 

 first pedigerous somite. Genital double-somite (Figs 

 21B,23B) wider than long, asymmetrical, left gonopore and 

 copulatory pore completely absent; right gonopore located 

 near posteroventral margin of double somite, anterior half 

 opening, covered by oval flap, possibly derived from leg 6; 

 outer half gonopore frilled with cuticular flap (Fig. 23 A); 

 copulatory pore (Fig. 23C) small, oval in shape, approxi- 

 mately 4.0 |xm in long axis and 1.0 jjliti in short axis, near 

 inner distal corner of gonopore (copulatory pore blocked by 

 spermatophore remnant); single seminal receptacle large, 

 about half width of somite, located ventromedially; copula- 

 tory duct short, curved. Anal operculum triangular as in M. 

 acutioperculum. 



Antennules asymmetrical, left longer than right, different 

 in fusion pattern and armature (see Fig. 22). Right antennule: 

 segments X to XII and XIV and XV fused only partly near 

 posterior margin; fusion pattern and armature as follows: 

 I-IV-9 + 2 aesthetascs (1-3 + aesthetasc, II-2, III— 2 + 

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

 thetasc, VIII-2, IX-X-4 + aesthetasc (IX-2 + aesthetasc, 

 X-2), XI-2 + aesthetasc, XII-2 + aesthetasc, XIII-1 + 

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

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

 XIX-2 + aesthetasc, XX-1 + aesthetasc, XXI-2 + aes- 

 thetasc, XXII-1, XXIII-1, XXIV-XXVIII-12 + 2 aes- 

 thetascs (XXI V-l + 1, XXV-1 + 1 + aesthetasc, 

 XXVI-XXVIII-8 + aesthetasc). Left antennule different 

 from right one in following: segments XII to XIV fused, with 

 5 setae and 2 aesthetascs (XII-2, XIII-1 + aesthetasc, XIV-2 

 + aesthetasc); segment XX with 2 setae and aesthetasc. 



Antenna: exopod (Figs 21E,25A) indistinctly 7-segmented; 

 setal formula 0,1,1,1,1,1,3 (2 setae and vestigial element). 

 Mandibular palp (Fig. 21F): endopod 1-segmented, almost 

 fused with basis, with 2 setae of unequal lengths; first exopod 

 segment carrying long seta, fifth segment bearing 2 normal 

 setae of unequal lengths. Maxillule (Fig. 21G): praecoxal 

 arthrite with 2 slender setae; coxal endite having 1 short seta; 

 coxal epipodite having 5 setae; basal seta absent; endopod 

 (indicated by arrowhead) 1-segmented, bulbous, with short 

 seta terminally. Maxilla: first and second praecoxal endites 

 with 1 seta plus 1 vestigial element and 2 setae respectively 

 (Fig. 21H); basal spine (Fig. 211) with 2 rows of short spinules 

 proximally. Maxilliped: fourth and fifth endopod, segments 



