Pachypygus tumidus, 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 : 117-120

Pachypygus tumidus sp. nov.

( Figs. 76 , 77 )

Type material. Holotype ♀ (dissected and mounted on a slide, MNHN-IU-2014-21237 ) from Herdmania pallida (Heller, 1878) (MNHN-IT-2008-4630 = MNHN S2/HER/24), CRRFCRCHO 001, Turtle Island , Palau (07°18.56 Ń, 134°30.10 É), 17 February 1995.

Etymology. The specific name is derived from the Latin tumid (= swollen), referring to the swollen body.

Description of female. Body ( Fig. 76A ) very similar in form to P. gibber , large, stout, moderately compressed, and firmly sclerotized. Bodylength 6.56 mm. Prosome 5-segmented. Third and fourth pedigerous somites expanded to form brood pouch; margin of brood pouch with distinct angle subdistally, visible in lateral view ( Fig. 76A ). Urosome ( Fig. 76B ) 6-segmented although fifth pedigerous somite obscure, largely fused with brood pouch. Genital and 4 free abdominal somites gradually narrowing distally, each much wider than long, 345×566, 351×468, 277×394, 191×326, and 147×295 μm, respectively. Anal somite ( Fig. 76C ) short, with pair of sclerotized, tapering ventral processes, each ornamented with spinules near tip. Caudal ramus ( Fig. 76C ) curved ventrally, tapering distally towards large terminal claw, 108 μm long, armed with 3 additional unequal claws 40, 18, and 16 μm long, plus 2 small setae positioned at 60% and 84% of ramus length.

Rostrum small. Antennule ( Fig. 76D ) small, tapering evenly towards tip; 9-segmented; armature formula 2, 14, 4, 4, 6, 4, 2, 2+aesthetasc, and 7+aesthetasc; all segments shorter than wide and all setae small and naked. Antenna ( Fig.76E ) stout and 3-segmented; coxashortand unarmed; allobasis with 1 small seta on subdistal inner margin; free endopod 1-segmented, 1.7 times as long as wide (85×50 μm), armed with 5 small setae plus terminal claw, as long as segment.

Labrum ( Fig. 76F ) broad, with 2 pairs of setulose lobes (tapering outer lobe and weak, rounded inner lobe) posterolaterally; ornamented with small patches of minute spinules either side of mid-posterior border. Mandible ( Fig. 76G ) with 5 teeth, middle one smaller, and 2 small proximal setae on coxal gnathobase; basis with 1 seta on subdistal medial margin, patch of setules on proximal medial margin and 2 rows of setules on ventral surface; exopod unsegmented, armedwith 5 setae (outer 2 longer than other 3); ornamented with about 3 rows of setules on ventral surface; endopod 2-segmented with 4 and 10 setae on first and second segments, respectively; first and fifth outer distal setae on second segment distinctly larger than other endopodal setae. Paragnath ( Fig. 76H ) as small lobe bearing 1 distal and 1 subdistal dentiform processes and setules on medial surface. Maxillule ( Fig. 77A ) with patch of setules on medial surface proximal to arthrite; armed with 10 setae on arthrite, 1 on coxal endite, 2 on epipodite, and 4 on medial margin of basis; exopod much wider than long, armed with 4 large setae distally; endopod with 6 setae, 3 each on first and second segments; second endopodal segment short, obscure. Maxilla ( Fig. 76I ) 5-segmented and armed as usual for genus; claw on basis slender and smooth; seta on second segment and one of 4 setae on third segment of endopod naked.Maxilliped ( Fig. 77B ) 3-segmented and armed with 9, 1, and 4 setae on first to third segments, respectively; articulations between segments incomplete; first segment ornamented with several short rows of minute spinules on both surfaces.

Legs 1–4 with 3-segmented rami ( Fig. 77 C–E). Inner seta on coxa large in legs 1 and 2, but small and naked in legs 3 and 4. Outer seta on basis of legs 1–4 small and naked. Inner distal spine on basis of leg 1 finely spinulose and longer than first endopodal segment. First exopodal segment of legs 2–4 less than twice as long as wide. Third exopodal segment of legs 1–4 about 1.5 times as long as wide. Inner setae absent on all exopodal segments of leg 4. First and third spines on third exopodal segment of legs 2 ( Fig. 77D ) and 3 longerthan other 2 spines. Inner seta on first endopodal segment of leg 4 shorter than other setae on endopod. 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
Legs 2& 30-1	30-1	1-0	I-1; I-0; III, I, 0	0-1; 0-2; 1, 2, 3
Leg 4	0-1	1-0	I-0; I-0; III, I, 0	0-1; 0-2; 1, 2, 2

Leg 5 ( Fig. 77F ) consisting of broad protopod and free exopod; protopod not demarcated from fifth pedigerous somite, bearing 1 naked seta at outer distal corner and scattered spinules at inner distal corner; exopodal segment gradually narrowingdistally, armedwith 1 small, spiniform seta and 1 naked seta, and ornamented with 2 groups of spinules on inner surface.

Male. Unknown.

Remarks. Pachypygus tumidus sp. nov. is very similar to P. gibber in body form. They also share the possession of 1 large and 3 smaller claws on the caudal ramus and an allobasis plus only 1 free endopodalsegment on the antenna, plus they have similar setation on legs 1–4. The main differences between P. tumidus sp. nov. and P. gibber are as follows: (1) the anal somite lacks a posterodorsal process (vs. present in P. gibber ); (2) the antennule narrows gradually and has 2 setae on the first segment (vs. first and second segments markedly broader than distal segments, and with 3 setae on the first segment in P. gibber ); (3) the basis of the antenna with 1 seta on inner margin (vs. with 1 seta on outer side in P. gibber ); (4) the first endopodal segment of the maxillule bears 3 setae (vs. 4 setae in P. gibber ); (5) the third exopodal segment of legs 2–4 is only 1.5 times longer than wide (vs. 2.5 times longer in P. gibber ); and (6) the inner margins of the exopods of legs 2–4 are smooth (vs. spinulose in P. gibber ). These differences are sufficient to justify the establishment of the new species.

Figures

FIGURE 76. Pachypygus tumidus sp. nov., female. A, habitus, right; B, urosome, ventral; C, distal part of abdomen, right; D, antennule; E, antenna; F, labrum; G, mandible; H, paragnath; I, maxilla. Scale bars: A, 1 mm; B, 0.2 mm; C, 0.1 mm; D–I, 0.05 mm.

FIGURE 77. Pachypygus tumidus sp. nov., female. A, maxillule; B, maxilliped; C, leg 1; D, leg 2; E, leg 4; F, leg 5. Scale bars: A, F, 0.05 mm; B–E, 0.1 mm.