Pachypygus curvatus Ooishi, 1961

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 : 114-117

Pachypygus curvatus Ooishi, 1961

( Figs. 74–75 )

Syn: Pachypygus australis Gotto, 1975 , new synonym.

Material examined. 6 ♀♀ (MNHN-IU-2018-1805) from Pyura sacciformis (Drasche, 1884) , Moorea M8; 27 ♀♀ (MNHN-IU-2018-1806) from P. sacciformis, Moorea M 17; 35 ♀♀ (MNHN-IU-2018-1807) from Herdmania momus (Savigny, 1816) , Port de Papeete, Tahiti; 5 ♀♀ (MNHN-IU-2018-1808) and 2 dissected ♀♀ from P. sacciformis , New Caledonia, NC 47; 10 ♀♀ (MNHN-IU-2018-1809) and 2 dissected ♀♀ (figured) from Herdmania pallida (Heller, 1878) , Port de Papeete, Tahiti, 1984; 12 ♀♀ (MNHN-IU-2018-1810) from H. pallida , Port de Noumea, New Caledonia, 1986; 1 ♀ (MNHN-IU-2018-1811) from from H. pallida Keehi Lagoon, Honolulu, November 1998; 1 ♀ (MNHN-IU-2015-4) from H. pallida , New Caledonia, warf de Thio; 1 ♀ (MNHN-IU-2015-15) from P. sacciformis, Tahiti, Stn T 48 (17°52.627’S 149°09.3305’W), depth 6 m.

Descriptionoffemale. Body ( Fig. 74A ) strongly bilaterally compressed, with highly sclerotized exoskeleton. Body length 4.39 mm. Brood pouch slightly longerthan wide, with rounded posterior margin inlateral view. Urosome ( Fig. 74B ) narrow, 6-segmented, widest at posterior region of genital somite, narrower anteriorly and posteriorly. Fifth pedigerous somite about 200×400 μm; genital and 4 free abdominal somites 423×515, 469×438, 369×345, 285×250, and 85×192 μm, respectively. Anal somite short, without ventralprominence or sclerotization. Caudal rami directed posteriorly; each ramus ( Fig. 74C ) graduallynarrowing distally, 3.6 times as long as wide (208×58 μm); armed distally with 4 small claws of equal length and 2 small setae both located at 42% of ramus length.

Rostrum elongate, 251×128 μm, evenly tapering, with truncate apex in ventral view ( Fig. 74D ) and dorsoventrally thick in lateral view ( Fig. 74E ). Antennule ( Fig. 74F ) 8-segmented; armatureformula 3, 17, 11, 6, 4, 2, 3, and 7+aesthetasc; first 2 segments broadened; 2 of 3 setae on first segment enlarged, annulated at base; second segment characteristically morethan 1.5 timeslonger than wide.Antenna ( Fig. 74G ) slender and elongate, consisting of coxa, basis and 2-segmented endopod; coxa short and unarmed; basis with 2 small setae at outer distal region, representing exopod; firstendopodal segment with 1 smallseta on inner margin; compound distal endopodal segment about 4.2 times longerthan wide,; armedwith 7 setae (3 distal setae pointed at tip) plus terminal claw, about half as long as segment.

Labrum ( Fig. 74H ) bearing dentiform process on semicircular posterolateral lobes, ornamented with patch of spinules on mid-ventral surface, and with setules on posterior margin, posterolateral lobes, and distal part of lateral margins. Mandible ( Fig. 74I ) bearing 5 teeth on coxal gnathobase; basis with 1 setaon medial margin and ornamented with fine spinules along medial margin between seta and distal border; exopod armed with 5 setae of equal length, exopodal setae hirsute proximally and pinnate distally; endopod with 4 and 10 setae on first and second segments, respectively, second inner distal seta smaller than adjacent setae on either side. Paragnath ( Fig. 74J ) with 2 dentiform processes, 1 distal and 1 mediodistal, and with denselysetulose medial surface. Maxillule ( Fig. 74K ) armedwith 10 setaeon arthrite, plus row of setules proximal to base of arthrite, 1 seta on coxal endite, 2 setae on epipodite; basis with 4 setae onmedial margin; exopod with cuticular fold subdistally and 4 setae distally; endopod 2-segmented, with 4 setae onmedial margin of first segment and 3 setae on small second segment. Maxilla ( Fig. 75A ) 5-segmented; syncoxawith 10 enditic setae arranged as 4, 1, 2 and 3 (including 1 very small seta); basis with 1 smooth claw plus 2 setae; endopod selnder with 1, 1, and 4 setae on first to third segments, respectively. Maxilliped ( Fig. 75B ) 3-segmented and armed with 9, 1, and 4 setae on first to third segments, respectively; articulation incomplete between first and second segments.

Legs 1–4 with 3-segmented rami. Inner seta on coxa of legs 1–4 well-developedand pinnate.Outersetaonbasis of legs smalland naked. Basisand first endopodalsegment of leg 1 with sensillae on ventral surface ( Fig. 75C ). Inner distal spine on basis of leg 1 small, about half as long as first endopodal segment. First exopodal segment of legs 2–4 ( Fig. 75 D–F) elongate, about 5 times as long as wide in legs 2 and 3 and about 4 times as long as wide in leg 4. Second and third exopodal segments of legs 2 and 3 small, both combined much shorter than first exopodal segment. Exopod of leg 4 enlarged; first segment lacking inner seta, ornamented with minute spinules on ventral surface; outer spines on second and third segments vestigial; third segment tapering, linguiform; proximalmost inner seta much larger than other inner setae on second and third segments. 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, 5	0-1; 0-2; 1, 2, 3
Leg 3	0-1	1-0	I-1; I-1; III, I, 4	0-1; 0-2; 1, 2, 3
Leg 4	0-1	1-0	I-0; I-1; II, II, 5	0-1; 0-2; 1, 2, 2

Leg 5 ( Fig. 75G ) protopodal region with about 10 transverse rows of spinules on ventral surface and 1 naked seta atouterdistal corner; exopodal segment elongate, about 6.0 times longer than wide (223×37 μm), ornamented with about 6 transverse rows of spinules along medial surface and armed with 2 unequal setae distally.

Male. Not found.

Remarks. Ooishi (1961) described this species as an associate of Pyura sacciformis (Drasche, 1884) (as Pyura michaelseni (Oka)) from the Inland Sea in Japan. Subsequently, Seo & Lee (1996) and Kim (2012) recorded the occurrence of this species from Ascidia sp. and Pyura sacciformis , respectively, in Korean waters.

Pachypygus australis Gotto, 1975 was described as an associate of Pyura pachydermatina (Herdman, 1881) collected off Sydney, Australia. Gotto (1975) noted that it shared numerous features in common with P. curvatus , such as the elongate second antennular segment, the location of the two proximal setae at the same level on the caudal ramus, the elongated first exopodal segment of legs 2–4, the linguiform third exopodal segment of leg 4, and the presence of multiple rows of spinules on the ventral surface of the protopod of leg 5. Gotto (1975) seems to have distinguished P. australis from P. curvatus largely on the basis of geographical separation, noting “were material available from areas to the north of Australia, this copepod might well be regarded merely as a geographical race of P. curvatus ”. The differences used by Gotto (1975) to separate these two species in his key referred to a minor setation character on leg 2, the pattern of tubercularornamentationon thethird exopodalsegment of leg 4, and the shape of the protopodal segment of leg 5. None of these appears to be a significant difference given our increased knowledge of the wide scale distribution of P. curvatus across the Pacific. Pachypygus australis is here treated as junior subjective synonym of P. curvatus .

Figures

FIGURE 74. Pachypygus curvatus Ooishi, 1961, female. A, habitus, left; B, urosome, ventral; C, right caudal ramus, ventral; D, rostrum ventral; E, rostrum, left; F, antennule; G, antenna; H, labrum; I, mandible; J, paragnath; K, maxillule. Scale bars: A, 0.5 mm; B, 0.2 mm; C–E, I, 0.1 mm; F–H, J, K, 0.05 mm.

FIGURE 75. Pachypygus curvatus Ooishi, 1961, female. A, maxilla; B, maxilliped; C, leg 1; D, leg 2; E, exopod of leg 3; F, leg 4; G, leg 5. Scale bars: 0.1 mm.