Pachypygus tenuirostris, 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 : 120-123

Pachypygus tenuirostris sp. nov.

( Figs. 78 , 79 )

Type material. Holotype ♀ (dissected and mounted on a slide, MNHN-IU-2014-21238 ) from Polycarpamytiligera (Savigny, 1816) , outer Récif Néokumbi , New Caledonia, NC 30, depth 20–30 m, Monniot coll., 09 March 1987.

Etymology. Thespecific name tenuirostris isderived from the Latin tenui (=slender) and rostr (=a beak), alluding to the narrow rostrum of the new species.

Descriptionoffemale. Body ( Fig. 78A ) compressed, with moderately sclerotized cuticle. Body length 5.56 mm. Cephalosome relatively small. Third pedigerous somite and brood pouch moderately expanded; brood pouch subcircular with rounded dorsal and posterior margins. Urosome 6-segmented, but fifth pedigerous somite obscure, largely incorporated into brood pouch. Genital somite shorter than first abdominal somite. Anal somite small, lacking process or spinules on ventral surface. Caudal ramus ( Fig. 78B ) about 2.4 times longer than wide (176×73 μm), tapering, armed with 2 setae and probably 4 claws (2 scars indicating positions of lost elements in holotype); 2 setae located at 60% and 72% of ramus length; 2 observed claws short and stout, only 11 μm long, slightly longer than wide.

Rostrum ( Fig. 78C ) evenly tapering, beak-like, 109×75 μm. Antennule small, clearly 9-segmented ( Fig. 78D ); firstandsecondsegments expanded; armatureformula 3, 16, 5, 4+aesthetasc, 5, 3+aesthetasc, 2, 2+aesthetasc, and 7+aesthetasc. Antenna ( Fig. 78E ) 4-segmented; coxa unarmed; basis about twice as long as wide, with 1 small seta representing exopod near outer distal corner; first endopodal segment unarmed; compound distal endopodal segment shorter than first segment, 82×57 μm, about 1.45 timesaslong as wide, and armedwith 8 small setae (grouped as 1, 3, 1, and 3) plus terminal claw, longer than segment.

Labrum ( Fig. 78F ) with semicircular posterolateral lobes, both spinulose, ornamented with 4 patches of spinuleson mid-ventral surface, setuleson lateral margins, andspinulesandsetulesatposterolateralcorners.Mandible ( Fig. 78G ) with 5 major teeth and 1 smallproximal seta on coxal gnathobase, plus 1 subsidiary tooth between 2 proximal major teeth; basis armed with 1 subdistal seta, ornamented with patch of setules proximally on medial margin and setulose lobe proximally on outer margin; exopod unsegmented with 5 setae, outermost distinctly larger than other 4; endopod 2-segmented with 4 and 10 setae on first and second segments, respectively; 4 outer distal setae on second endopodal segment subequal in length. Paragnath ( Fig. 78H ) with 2 dentiform processes, located distally and subdistally, plus ornamentation of dense setules on medial margin. Maxillule ( Fig. 78I ) and maxilla ( Fig. 78J ) similar to those of P. curvatus . Maxilliped ( Fig. 79A ) distinctly 3-segmented, armedwith 9, 1, and 4 setae on first to third segments, respectively.

Legs 1–4 with 3-segmented rami ( Fig. 79 B–E). Inner coxal seta large in legs 1 and 2, rudimentary in leg 3, and absent in leg 4. Outer seta on basis pinnate and moderately large in leg 1, but small and naked in legs 2–4. Inner distal spine on leg 1 basis 88 μm long, as long as first endopodal segment. First exopodal segment of legs 2–4 moderately elongate, about 2.5 timeslongerthan wide. Third exopodal segment of legs 2–4 also about 2.5 times longer than wide, with smooth, linear inner margin. Endopodal segments of leg 1 with sensillae on anterior surface. Armature formula for legs 1–4 as follows:

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

Leg 5 ( Fig. 79F ) protopod longer than wide, unornamented with rudimentary outer seta. Free exopodal segment about 3.2 timeslongerthan wide (191×59 μm), armed distally with 1 small, strongly tapering seta (or spine) and 1 small, naked seta; ornamented with 3 rows of spinules on medial surface.

Male. Unknown.

Remarks. In the possession of a 2-segmented endopod in the antenna, P. tenuirostris sp. nov. can be readily differentiated from P. gibber , P. globosus , and P. tumidus sp. nov., all three of which have an allobasis and only one free segment in the endopod. The two other congeners, P. curvatus and P. macer , which share a 2- segmented endopod can clearly be distinguished from the new species: in P. curvatus the second segment of the antennule is elongate, the first exopodal segment of legs 2–4 and the exopod of leg 5 are also elongate, whereas in the new species these segments are not elongate. In P. macer the brood pouch tapers in lateral view, the compound distal endopodal segment of the antenna is more than twice as long as wide (compared to only 1.45 times as long as wide in P. tenuirostris sp. nov.), and the second exopodal segment of leg 2 and the first exopodal segment of leg 3 both lack an inner seta (which is present in the new species).

Figures

FIGURE 78. Pachypygus tenuirostris sp. nov., female. A, habitus, right; B, left caudal ramus, outer; C, rostrum; D, antennule; E, antenna; F, labrum; G, mandible; H, paragnath; I, maxillule; J, maxilla. Scale bars: A, 0.5 mm; B–D, F, H, 0.05 mm; E, G, I, J, 0.1 mm.

FIGURE 79. Pachypygus tenuirostris sp. nov., female. A, maxilliped; B, leg 1; C, leg 2; D, leg 3; E, leg 4; F, leg 5. Scale bars: 0.1 mm.