Pachypygus Sars G. O., 1921

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 : 105

Genus Pachypygus Sars G. O., 1921

Diagnosis. Female body with large brood pouch, often extending from third pedigerous somite back, incorporating fourth pedigerous somite. Fifth pedigerous somite partly fused to brood pouch but well defined in some species. Freeurosome 5- or 6-segmented in female, 6-segmented in male. Anal somite with processes in some species. Caudal rami curved; armed with 4 claws and 2 setae. Rostrum well-developed. Female antennule 8- or 9-segmented with first and second segments typically broader than distal segments: segmental fusion pattern I-II, III-XI, XII-XIV, XV-XVI, XVII-XX, XXI-XXIII, XXIV, XXV, XXVI-XXVIII; or with additional compound segment XII-XVI in 8-segmented species. Male antennule typically 8-segmented; non-geniculate. Antenna consisting of coxa, basis, and 2-segmented endopod with compound distal segment bearing terminal claw; or with allobasis incorporating first endopodal segment and 1-segmented free endopod; exopod reduced to seta or absent. Mandible with well developed coxal gnathobase and biramous palp armed with 1 seta on basis, 5 setae on exopod, and 4 and 9 or 10 setae on first and secondendopodal segments, respectively. Maxillulewith 9 or 10 setae on arthrite, 1 on coxal endite, 2 on epipodite, and 3 on medial margin of basis; exopod unsegmented with 4 setae distally; endopod 2-segmented, with variable setation. Maxilla indistinctly 5-segmented, syncoxal endite formula 4, 1, 2, 3, or reduced; basis with claw plus 2 setae; 3-segmented endopod with setal formula 1, 1, 3/4. Maxilliped 3-segmented and armedwith 9 setae on first segment, 1 on second and 3 or 4 (rarely 2) on third. Legs 1–4 biramous and typically with 3-segmented rami (endopods of legs 2–4 only 2-segmented in one species); first exopodal segments of legs 2–4 elongate in many species; armatureformula of female typically:

	CoxaBasis Exopod			Endopod
Leg 1	0-1	1-I	I-1; I-1; III, I, 0/4	0-1; 0-1; 1, 2, 3
Legs 2 & 30-1		1-0	I-1; I-1; III, I, 0	0-1; 0-2; 1, 2, 3
Leg 4	0-1	1-0	I-0; I-1; II, I,0	0-1; 0-2; 1, 2, 2

Inner setae on exopodal segments of legs present or absentaccordingto species, andusuallysexually dimorphic. Basis and first two endopodal segments of leg 1 typically ornamented with scattered sensillae on anterior surface. Leg 5 consisting of large protopod fused to pedigerous somite and free exopodal segment armed with 2 elements.

Type species. Pachypygus gibber ( Thorell, 1859) , by original monotypy.

Remarks. Six nominal species have been described in the genus Pachypygus , of which P. spinosus Kim & Moon, 2011 was described on the basis of a juvenile, possibly of P. gibber . It has a small brood pouch, only 2 setae (not the usual 3) on the first antennular segment, 3 setae (not 4) on the first endopodal segment of the mandible, and 7 setae (not 9) on the first maxillipedal segment. Pachypygus australis Gotto, 1975 known from Australia has no distinguishing features that allow it to be differentiated from P. curvatus Ooishi, 1961 , as discussed below in the remarks of the latter species. Thus, only four species are considered as valid: P. gibber , P. macer Illg, 1958 , P. curvatus , and P. globosus Ooishi, 1963 . The first three of these are redescribed below.