Nobinerilla exilipes, Kim & Boxshall, 2020

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 : 285

Nobinerilla exilipes gen. et sp. nov.

( Figs. 190 , 191 )

Typematerial; Holotype (intact ♀, MNHN-IU-2014- 21295 ) anddissectedparatype (♀, figured) from Symplegma alterna Monniot C., 1988 , Uie Bay, New Caledonia, depth 18 m, Monniot coll., 11 March 1987.

Etymology. The name is derived from the Latin exil (=slender) and pes (=a foot) and refers to the slender exopod of leg 5.

Description of female. Body ( Fig. 190A ) compressed, 1.51 mm long. Cephalosome and metasome fused; metasome unsegmented, strongly inflated, 1.13×0.84 mm in lateral view, broad in dorsal two-thirds and narrow in ventral third. Free urosome ( Fig. 190B ) stout, 5-segmented, graduallynarrowing posteriorly: genitalsomite longest, 102×257 μm; 4 abdominalsomites 90×207, 70×180, 50×170, and 75×127 μm, respectively. Caudal ramus ( Fig. 190C ) 2.1 times longer than wide (74×35 μm) and as long as anal somite: armed with 6 naked setae; outer lateral and dorsal setae positioned at 52 and 67% of ramus length, respectively; distal longest seta slightly longer than caudal ramus.

Rostrum ( Fig. 190D ) widerthan long (68×90 μm) with rounded apex and slightly concave lateral margins. Antennule ( Fig. 190E ) about 190 μm long and 7-segmented; armatureformula: 3, 16, 8+aesthetasc, 4, 2+aesthetasc, 3+aesthetasc, and 7+aesthetasc; all setae naked.Antenna ( Fig. 190F ) slender, withshort coxa; basis 2.6 timeslongerthan wide, unarmed; firstendopodal segment about 1.7 times longer than wide (55×32 μm); compound distal endopodal segment distinctly narrower than first and 4.1 times longer than wide (85×21 μm); armed with 6 small setae plus small terminal claw, about one-thirdaslongas segment.

Labrum ( Fig. 190G ) withlarge, denselysetulose posteromedianlobeandsetuloseposteriormargin.Mandible ( Fig. 190H ) with 5 teeth, including 2 smallproximal teeth, on coxal gnathobase; basis with small medial seta; exopod with 5 setae, 2 distal setae shorter than proximal 3; endopod with 4 and 5 setae on first and second segments, respectively. Maxillule ( Fig. 190I ) with 9 setaeon arthrite, 1 broad setaon coxal endite; 2 on epipodite; 3 on basis, 4 on exopod, and 3 on endopod. Maxilla ( Fig. 191A ) 5- segmented; syncoxa with 9 setae (3, 1, 2, and 3 on first to fourth endites, respectively), clawplus 1 setaon basis, and 1, 1, and 2 setaeon first to third endopodal segments, respectively. Maxilliped ( Fig. 190J ) unsegmented with 10 setae medially and 1 outer distal seta.

Legs 1–4 ( Fig. 191 B-E) with 3-segmented rami. Inner coxal seta absent in legs 1, 2, and right legs 3 and 4, but present in left legs 3 and 4; inner coxal seta on left leg 4 rudimentary. Outer setaon basis large in leg 1, but small in legs 2–4. Inner distal spine absent on basis of leg 1 ( Fig. 191B ). Second exopodal segment of leg 1 lacking inner seta. Three inner setae on endopod of leg 1 small, shorter than width of endopod at base. Exopod 1.3 times longer thanendopod inleg 1 and 1.4 timeslongerinlegs 2–4. First exopodal segment longer than other exopodal segments in all legs. First and second endopodal segments of legs 2–4 with bilobed, densely setulose anterodistal margins. Third endopodal segment of legs 2–4 not elongate, more or less twice as long as wide and only slightly longer than second endopodal segment. Armature formula for legs 1–4 as in N. filipes .

Leg 5 ( Fig. 191F ) with naked outer distal seta on protopod. Exopod about 4.4 times longer than wide (109×25 μm), with 5 rows of fine spinules on inner surface; distal and subdistal setae subequal in length, both naked.

Male. Unknown.

Remarks. Nobinerilla exilipes gen. et sp. nov. is very similar to N. filipes . They have several unusual features in common: (1) the mandible bears only 5 setae on the second endopodal segment; (2) the basis of leg 1 lacks an inner distal spine; (3) the second exopodal segment of leg 1 lacks an inner seta; (4) the endopod of the maxillule has 3 setae; and (5) the positions of the two setae on the elongate exopod of leg 5 are also characteristic, one on the apex and the other subdistally on the outer margin.

Nevertheless, these two species can be separated by the following differences: (1) the body of N. exilipes gen. et sp. nov. (1.51 mm long) is much smaller than that of N. filipes which is 2.55 and 3.26 mmlong in our specimens and 2.28 mm long in the specimen of Illg & Dudley (1961); (2) the caudalramus of N. exilipes gen. et sp. nov. is about 2.1 times longer than wide and the longest caudal seta is slightly longer than the caudal ramus itself, whereas the caudal ramus of N. filipes is 3.1 times longer than wide and all its caudal setae are less than half the length of the caudal ramus; (3) all setae on the antennule are naked in N. exilipes gen. et sp. nov., whereas several antennular setae are pinnate in N. filipes ; (4) the third endopodal segment of legs 3 and 4 of N. exilipes gen. et sp. nov. is not elongate, and is only slightly longerthan the second exopodal segment and about twice as long as wide, compared to that of N. filipes which is elongate, more than twice as long as the second endopodal segment and morethan 4 timeslongerthan wide; and (5) the exopod of leg 5 of N. exilipes gen. et sp. nov. (109 μm long, 4.4 times longerthan wide) is distinctly shorter than that of N. filipes (258 μm long, 6.3 times longer than wide in our specimen). These differences are sufficient to justify the establishment of the new species.

Figures

FIGURE 190. Nobinerilla exilipes gen. et sp. nov., female. A, habitus, right; B, urosome, ventral; C, caudal ramus, ventral; D, rostrum; E, antennule; F, antenna; G, labrum; H, mandible; I, maxillule; J, maxilliped. Scale bars: A, 0.2 mm; B, 0.1 mm; C, F–H, 0.05 mm; D, E, I, J, 0.02 mm.

FIGURE 191. Nobinerilla exilipes gen. et sp. nov., female. A, maxilla; B, leg 1; C, left leg 2; D, left leg 3; E, left leg 4; F, leg 5. Scale bars: 0.05 mm.