Pentachaetusspinatus, 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 : 494-497

Pentachaetusspinatus gen. etsp. nov.

( Figs. 328 , 329 )

Typematerial. Holotype (intact ♀, MNHN-IU-2014- 21378 ) anddissectedparatype (♀, MNHN-IU-2014- 21379) from unidentified immature host of family Didemnidae, Canal Woodin, Grande Terre New Caledonia, depth 32 m, Monniot coll., 12 March 1987.

Etymology.Thespecificnamereferstothepossession of the paired spiniform posterolateral processes on the dorsalcephalic shield.

Descriptionoffemale. Body ( Fig. 328A ) slightly expanded; bodylength 0.99 mm. Prosome curved ventrally: cephalosome well-defined from metasome; dorsal cephalic shield extended ventrolaterally and bearing paired posteroventral process; processes thin, straight, thorn-like, 25 μm long, ornamented with 4 or 5 fine spinules distally on dorsal margin ( Fig. 328B ). Metasome with 2 incomplete articulations dividing first to third pedigerous somites; third and fourth pedigerous somites fused, both containing large eggs inside. Free urosome ( Fig. 328C ) cylindrical, graduallynarrowing posteriorly:genitalsomite 42×97 μm, 4 abdominalsomites sparsely ornamented with setules on all surfaces, 47×86, 48×75, 36×67, and 54×62 μm, respectively. Anal somite with narrow posteromedian incision. Caudal ramus ( Fig. 328D ) tapering, about 3.3 timeslongerthan wide (65×20 μm), and ornamented with few setules; armed with 5 setae (outer lateral, dorsal, and 3 distal), all setae naked and longer than width of ramus at base, largest seta 105 μm long, 1.6 times longer than ramus, second longest adjacent seta 60 μm long; outer lateral and dorsal seta positioned at 27 and 43% of ramus length, respectively.

Rostrum ( Fig. 328E ) subtriangular, 69×70 μm, setulose, with blunt apex.Antennule ( Fig. 328F ) relatively slender, 147 μmlong, 6-segmented; armatureformula 2, 15, 5, 3+aesthetasc, 4+aesthetasc, and 10+2 aesthetascs; all setae naked; aesthetascs setiform (thin and short). Antenna ( Fig. 328G ) 3-segmented, comprising coxa, basis and unsegmented endopod; coxa and basis unarmed; endopod about 4.1 times longer than wide (62×15 μm) and as long as basis: armed with 6 setae arranged as 1, 2, and 3; proximalmost seta longer than width of endopod; 3 distal setae bluntly tipped, all shorter than claw; terminal claw small, about 20 μm long, one-quarter as long as endopod.

	Coxa	Basis	Exopod	Endopod
Leg 1	0-0	1-I	I-1; I, 1, 5 0-1;	0-1; 1, 2, 3
Leg 2	0-0	1-0	1-0; 1-0; 3, 1, 5	0-0; 0-0; 0, 2, 3
Leg 3	0-0	1-0	1-0; 1-0; 3, 1, 5	0-0; 1, 2, 2
Leg 4	0-0	1-0	1-0; 1-0; 3, 1, 4	0-0; 1, 2, 1

Labrum soft, hardly discernible. Mandible ( Fig. 328H ) with relatively narrow coxal gnathobase bearing 5 acute teeth and 1 small seta: basis with 1 setaonmedial margin: exopod with 5 setae, outermost only 0.6 times as long as other 4 setae: endopod 2-segmented; first segment with 1 proximally broadened seta; second segment with 4 unequal setae (proportional lengths of setae 1, 2, 3, and 2.2 from inner to outer). Maxillule ( Fig. 328I ) with 9 setae on arthrite, 1 on each epipodite and basis, 4 on exopod and 3 on endopod (endopodal setae unequal in length, medial seta shortest and outer longest). Maxilla ( Fig. 329A ) 4- segmented, armed with 4, 2, and 2 setae on first to third endites on syncoxa, claw plus 2 very unequal setae on basis, and 1 and 3 setae on first and second endopodal segments, respectively; claw on basis ornamented with several minute spinules distally on concave margin. Maxilliped ( Fig. 328J ) unsegmented, lobate, armedwith 6 setae and ornamented with spinules on outer surface.

Legs 1–4 ( Fig. 329 B-F) lacking inner coxal seta. Outer seta on basis pinnate in leg 1, but naked in legs 2–4. Leg 1 bearing small inner distal spine on basis, 12 μm long; exopod 2-segmented, with vestige of articulation on compound distal segment; 2 inner proximal setae on third endopodal segment markedly elongate, about 3 times longerthan ramus. All setae on legs 2–4 naked. Leg 2 with 3-segmented rami. Legs 3 and 4 with 3-segmented exopods and 2-segmented endopods; both legs slightly asymmetrical in length and in shape of setae on left and right sides; outer setae on exopod and all setae on endopod attenuated in left leg but bluntly tipped in right leg, and inner setae on third exopodal segment long in left leg but shorter in right leg (cf. Fig. 329D and E ). Armature formula for legs 1–4 as follows:

Leg 5 ( Fig. 329G ) consistingof protopodal lobe bearing digitiform outer distal process tipped with 1 seta, plus pointed inner (exopodal) process tapering distally from broad base and bearing 1 seta on outer margin.

Male. Unknown.

Remarks. Unlike its two congeners described below, Pentachaetusspinatus gen. etsp. nov. has thin, spiniform, horn-like processes posterolaterally on the dorsal cephalic shield. It also has a triangular rostrum which is as long as wide, the outer setaon the exopod of the mandible is 0.6 times as long as other 4 exopodal setae, and the inner exopodal process of leg 5 is broadened at its base. These and other differences between the species of Pentachaetus gen. nov. are summarised in Table 11 .

Figures

FIGURE 328. Pentachaetus spinatus gen. et sp. nov., female. A, habitus, right; B, posterolateral process of cephalic shield; C, leg 5 and urosome; D, left caudal ramus, lateral; E, rostrum; F, antennule; G, antenna; H, mandible; I, maxillule; J, maxilliped. Scale bars: A, 0.1 mm; B, D–J, 0.02 mm; C, 0.05 mm.

FIGURE 329. Pentachaetus spinatus gen. et sp. nov., female. A, maxilla; B, leg 1; C, left leg 2; D, left leg 3; E, right leg 3; F, left leg 4; G, leg 5. Scale bars: 0.02 mm.