Pentachaetus longisetatus, 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 : 498-503

Pentachaetus longisetatus gen. et sp. nov.

( Figs. 332 , 333 )

Typematerial. Holotype (intact ♀, MNHN-IU-2014- 21381 ) , paratype (intact ♀, MNHN-IU-2014-21382), and dissectedparatype (♀, figured) from Leptoclinides sp. (MNHN-IT-2008-4861 = MNHNA 2/ LEP /111), CRRF CRCHO 561, on reef slope, Baluan, Papua New Guinea (02°32,27’S, 147°17.97’E), depth 24 m, L. Martin coll., 22 June 2003.

Etymology. The specific name refers to the long terminal seta on the caudal ramus, which is distinctly longerthan that of its congeners.

Descriptionoffemale. Body ( Fig. 332A ) small, strongly curved ventrally; body length 638 μm. Prosome comprising cephalosome and 4 metasomites; dorsal cephalic shield large, bearing tapering, acutely pointed horn-like processes posterolaterally on each side ( Fig. 332B ). Fourth pedigerous somite not expanded; fifth pedigeroussomite not defined. Free urosome ( Fig. 332C ) 5-segmented, curved ventrally, setulose on dorsal surface. Anal somite ( Fig. 332D ) 37×43 μm. Caudal ramus ( Fig. 332D ) about 3.2 times longer than wide (41×13 μm) and slightly longer than anal somite: armed with 5 naked setae; longest distal seta 92 μm long, 2.5 times longer than second longest adjacent seta; 2 proximal setae positioned at 31 and 41% of ramus length.

Rostrum ( Fig. 332E ) about 1.3 timeslongerthan wide, tapering towards blunt apex. Antennule ( Fig. 332F ) about 95 μm long, 6-segmented; setation indeterminable due to damage. Antenna ( Fig. 332G ) 3-segmented; coxa and basis unarmed; endopod 3.2 times longer than wide (32×10 μm) and as long as basis: armed with 4 setae (grouped as 1, 1, and 2) and several spinules subdistally on outer margin; terminal claw small, strongly curved.

Labrum soft, not dissected. Mandible ( Fig. 332H ) with broad coxalgnathobase bearing 5 pointed teeth and 1 small seta: basiswith 1 setaonmedial margin: exopod with 5 setae, distal 4 becoming shorter from medial to outer; outermost seta about 0.4 times as long as adjacent outer distal seta: endopod with 1 and 4 setae on first and second segments, respectively; seta on first segment markedly expanded proximally; proportional lengths of 4 setae on second segment 8:11:20:11 from medial to outer. Maxillule ( Fig. 332I ), maxilla ( Fig. 333A ), and maxilliped ( Fig. 333B ) armed as in P. palauensis gen. et sp. nov.

Legs 1 and 2 ( Fig. 333C, D ) with 3-segmented rami, but articulation incomplete between second and third exopodal segments of leg 1. Legs 3 and 4 ( Fig. 333 E-F) with 3-segmented exopods and 2-segmented endopods; second endopodal segment of legs 3 and 4 elongate, about 4 timeslongerthan wide. Innercoxalsetaabsentinlegs 1–4. Outer setaon basis large and pinnate in leg 1, but small and naked in legs 2–4. Inner distal spine on basis of leg 1 small, 7 μm long. Outer spine on first exopodal segment of leg 1 serrate, 15 μm long. Legs 2–4 slightly asymmetrical between left and right sides: setae on third exopodal segment of left leg longer than those of right leg, but setae on second endopodal segment of left leg shorter than those of left leg (cf. Fig. 333E and G ). Armature formula for legs 1–4 as in P. palauensis gen. et sp. nov. except second endopodal segment of leg 3 armed with 4 setae (formula 1, 1, 2).

Leg 5 ( Fig. 333H ) similartothatof P. palauensis gen. et sp. nov., but seta between outer and inner processes positioned closer to inner (exopodal) process.

Male. Unknown.

Remarks. In P. longisetatus gen. etsp. nov. the posterolateral horn-like processes on the dorsal cephalic shield taper towards an acutely pointed tip, the rostrum is elongate, the outermost seta on the mandibular exopod is short (only 0.4 times as long as the adjacent outer distal seta), and the endopod of leg 3 is armed with 4 setae. These features differentiate P. longisetatus gen. et sp. nov. from its two congeners (see Table 11 ).

Figures

FIGURE 332. Pentachaetus longisetatus gen. et sp. nov., female. A, habitus, right; B, cephalic horn; C, leg 5 and urosome, right; D, anal somite and caudal rami, dorsal; E, rostrum; F, antennule, with setation omitted; G, antenna; H, mandible; I, maxillule. Scale bars: A, C, 0.05 mm; B, I, 0.01 mm; D–H, 0.02 mm; I, 0.01 mm.

FIGURE 333. Pentachaetus longisetatus gen. et sp. nov., female. A, maxilla; B, maxilliped; C, leg 1; D, leg 2; E, leg 3; F, right leg 4; G, left leg 4; H, leg 5. Scale bars: A, B, 0.01 mm; C–H, 0.02 mm.