Remex obesus Monniot C., 1983

Kim, Il-Hoi & Boxshall, Geoff A., 2020, Untold diversity: the astonishing species richness of the Notodelphyidae (Copepoda: Cyclopoida), a family of symbiotic copepods associated with ascidians (Tunicata), Megataxa 4 (1), pp. 1-6 : 454-458

Remex obesus Monniot C., 1983

( Figs. 301–303 )

Material examined. 6 ♀♀, 4 ♂♂ (MNHN-IU-2018- 1890) from Ascidiainterrupta Heller, 1878 , Riviere Sens, Gaudeloupe; 5 ♀♀ (MNHN-IU-2018-1891) from A. interrupta, Grande Anse , Guadeloupe; 18 ♀♀, 4 ♂♂ (MNHN-IU-2018-1892)and dissected 2 ♀♀, 1 ♂ (figured) from A. interrupta, Pointe des Salines , Martinique; 10 ♀♀, 7 ♂♂ (MNHN-IU-2017-2079) from A. interrupta, MADIBENTHOSStnAR 063 (14°27.3 Ń, 60°55.5 Ẃ), depth 21-26 m, 10 September 2016; 10 ♀♀ (MNHN-IU-2017-2144) from A. interrupta, MADIBENTHOS Stn AR 051 (14°29.6 Ń, 61°05.5 Ẃ), depth 5-25 m, 07 September 2016; 3 ♀♀, 1 ♂ (MNHN-IU-2017-2148) from A. interrupta, MADIBENTHOSStnAR 172 (14°24 Ń, 60°49.6 Ẃ), depth 19-24 m, 12 September 2016.

Descriptionoffemale. Body ( Fig. 301A ) small, slightly depressed, consistingof cephalosome, neck region, expanded brood pouch, and narrow urosome. Body length 697 μm in dissected specimen. Cephalosome 91×158 μm, with rounded anterior and lateral margins. Neck region comprising first to third pedigerous somites. Brood pouch 303×274 μm, formed by fused fourth and fifth pedigerous somites, bearing leg 4 anteroventrally and leg 5 posteroventrally ( Fig. 301A, B ). Freeurosome ( Fig. 301B ) 5-segmented, curved dorsally: genitalsomite 27×74 μm; 4 abdominalsomites 61×74, 53×56, 30×48, and 32×42 μm, respectively. Caudalramus ( Fig. 301B, C ) elongate, about 17 times longer than wide (250×15 μm), whip-like, flexible: armedwith 1 proximal and 5 distal, small setae; proximal seta positioned at 20% of ramus length.

Rostrum ( Fig. 301D ) shield-like, articulated at base, 1.7 times longerthan wide (24×14 μm), truncated distally. Antennule ( Fig. 301E ) consistingof 3 broad proximal segments and 4 narrower distal segments; armature formula indistinctly 2, 14, 4, 1 aesthetasc, 1 aesthetasc, 2+aesthetasc, and 8+3 aesthetascs. Antenna ( Fig. 301F ) 3-segmented, consistingof unarmed coxa and allobasis, and unsegmented free endopod bearing 1 seta in middle and several minute spinules subdistally on inner margin; terminal claw slender, about 0.7 times as long as free endopodal segment.

Labrum ( Fig. 301G ) small, subcircular, with narrow, truncate apex. Mandible ( Fig. 301H ) with 5 teethand 2 small setaeon coxal gnathobase: basis with 1 seta subdistally onmedial margin: exopod widerthan long, armed with 5 setae (medial and outer setae shorter than 3 distal setae): endopod clearly articulated from basis and clearly 2-segmented, armedwith 3 and 7 setae on firstandsecondsegments, respectively; 2 of 3 setaeon first segment naked and much smaller than distal seta. Maxillule ( Fig. 301I ) with 8 setae on arthrite, 1 on each coxal endite and epipodite, 3 on basis, 4 on exopod and 5 on endopod; all setae on exopod and 3 outer setae on endopod bluntly tipped. Maxilla ( Fig. 301J ) 3-segmented, consistingof syncoxa, basis, and 1-segmented endopod; setae on syncoxa arranged as 4, 1, 2, and 3; basis with strong claw plus 2 unequal setae; endopod small with 4 naked setae and 1 distinct, spiniform process. Maxilliped ( Fig. 302A ) 2-segmented; armedwith 5 pinnate setaeon first segment and 3 naked setae on second.

Legs 1–4 ( Fig. 302 B-E) with 3-segmented exopods and 2-segmented endopods; exopods distinctly longer than endopods. Innercoxalsetaabsentinlegs 1–4. Outer seta on basis large in leg 1, vestigial in leg 2, and small in legs 3 and 4. Basis of leg 1 with inner distal seta (not spine). Exopod of leg 3 twice as long as endopod. Leg 4 with extremely unequal rami; exopod about 10 times longerthan endopod; 3 exopodal segments 4:2: 3 in proportional lengths; third exopodal segment tipped with 3 smallsetae (or spines), median seta curved, hook-like. Armature formula for legs 1–4 as in generic diagnosis. Leg 5 ( Fig. 302F ) represented by small exopodal lobe bearing 2 unequal setae.

Descriptionofmale. Body ( Fig. 303A ) extremely slender, graduallynarrowingposteriorly, 11-segmented. Body length 773 μm. Prosome-urosome boundary obscure. Caudal rami ( Fig. 303A ) divergent, slender, about 13 times longer than wide (209×16 μm) and 4.6 times longerthan anal somite.

Rostrum ( Fig. 303B ) directed anteriorly, fused to dorsal cephalic shield, with parallel lateral margins and convex distal margin. Antennule 7-segmented ( Fig. 303C ); proximal 3 segments broader than distal 4 segments; shortest fourth segment obscure; armature formula 2, 14, 4, 0, 3, 4, and 11+aesthetasc. Antenna ( Fig. 303D ) robust, chelate; small coxa unarmed; basis broadened, with 3 dentiform processes along medial margin, proximal process opposing tip of terminal claw; endopod unsegmented, armedwith 1 setasubdistally; terminal claw clearly articulated from and as long as endopod. Labrumand maxillulesimilar tothose of female. Mandible with 3 large setaeon first endopodal segment. Maxilla with smaller dentiform process on endopod than in female. Maxilliped with indistinct articulation between segments.

Legs 1 lacking outer setaon basis. Leg 2 as in female. Leg 3 with large inner seta on first endopodal segment. Leg 4 ( Fig. 303F ) very different from that of female; exopod 2.2 timeslongerthan endopod, with 4 bluntly tipped setae (1 on first and 3 on third segments, as in female); endopod with unarmed first segment, but armedwith 3 setae on second segment. Leg 5 ( Fig. 303E ) represented by 1 seta. Leg 6 ( Fig. 303E ) represented by 2 setae on genital operculum.

Remarks. The specimens examined here were collected from the type host at the type locality. Some parts of the original description of this species are not in accord with our observations. The above redescription includes corrections and clarifications of the original description, mainly with regard to body segmentation, the segmentation and setation of the mandible and maxilla, the presence of a maxilliped, and the armature of legs 1 and 2.

Figures

FIGURE 301. Remex obesus Monniot C., 1983, female. A, habitus, dorsal B, urosome, ventral; C, right caudal ramus, dorsal; D, rostrum; E, antennule; F, antenna; G, labrum; H, mandible; I, maxillule; J, maxilla. Scale bars: A, 0.1 mm; B, C, 0.05 mm; D–J, 0.01 mm.

FIGURE 302. Remex obesus Monniot C., 1983, female. A, maxilliped; B, leg 1; C, leg 2; D, leg 3; E, leg 4; F, leg 5. Scale bars: A, F, 0.01 mm; B–E, 0.02 mm.

FIGURE 303. Remex obesus Monniot C., 1983, male. A, habitus, dorsal; B, rostrum; C, antennule; D, antenna; E, fifth pedigerous and genital somites, ventral; F, leg 4. Scale bars: A, 0.1 mm; B–F, 0.02 mm.