Pachypygus macer Illg, 1958

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 : 110-114

Pachypygus macer Illg, 1958

( Figs. 71–73 )

Material examined. 12 ♀♀, 10 ♂♂ (MNHN-IU-2018- 1800) from Microcosmus exasperatus Heller, 1878 , mangrove, Puerto Rico; 12 ♀♀, 4 ♂♂ (MNHN-IU-2018- 1801) and dissected 2 ♀♀, 1♂ from M. exasperatus , marina of Bas du Fort, Guadeloupe; 2 ♀♀ (MNHN-IU-2018-1802) from Styela canopus (Savigny, 1816) , marina of Bas du Fort, Guadeloupe; 1 ♀ (MNHN-IU-2018-1803) from M.exasperatus , marinaof Riviere Sens, Guadeloupe; 3 ♀♀, 2 ♂♂ (MNHN-IU-2018-1804 and dissected 1 ♀, 1 ♂ (figured) from from Pyura styeliformis Monniot F. & Monniot C., 2001 , marine lake, Palau (07°16.80 Ń, 134°25.92 É), depth 0.5 m, 06 April 2004.

	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-0; III, I, 0	0-1; 0-2; 1, 2, 3
Leg 3	0-1	1-0	I-0; 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

Descriptionoffemale. Body ( Fig. 71A ) compressed, 2.65 mm long. Brood pouch tapering in distal third. Urosome ( Fig. 71B ) 6-segmented, including well-defined fifth pedigerous somite (137×315 μm); genital and 4 free abdominalsomites 178×274, 241×259, 200×215, 96×156, and 63×130 μm, respectively. Anal somite ( Fig. 71C ) smaller than other abdominal somites; ventral surface well-sclerotized, but lacking process or ornamentation of spinules posteroventrally. Caudalramus ( Fig. 71D ) slightly curved ventrally, about 3.1 times longer than wide (133×43 μm), and armed with 1 terminal and 3 subdistal claws plus 2 small setae; terminal claw about twice as long as 3 smaller claws; 2 setae positioned at 50% and 72% of ramus length.

Rostrum ( Fig. 73A ) triangular, slightly longer than wide.Antennule( Fig.71E )9-segmented;armatureformula 3, 16, 5, 4, 5, 3, 2, 2+aesthetasc, and 7+aesthetasc; first two segments expanded; articulation indistinct between two terminal segments. Antenna ( Fig. 71F ) consisting of shortcoxa, basis, and 2-segmented endopod; basiswith 1 or 2 minute setae distally representing exopod; first endopodal segment separate, unarmed; compound distal endopodal segment 2.7 times longer than wide (81×30 μm); armed with 8 or 9 small setae plus terminal claw, more than half length of segment.

Labrum ( Fig. 71G ) with concave posterior margin, ornamented with setules posterolaterally and fine spinules on ventral surface. Mandible ( Fig. 71H ) with same setation pattern as in P. gibber , but 5 setae on exopod subequalin length; ornamented with setules only on inner margin of basis. Paragnath ( Fig. 73B ), maxillule ( Fig. 72A ) and maxilla ( Fig. 72B ) as in P. gibber . Maxilliped ( Fig. 71I ) 3-segmented with 9, 1, and 4 setaeonfirst to third segments; articulation incomplete between first and second segments.

Legs 1–4 ( Fig. 72 C–F) with 3-segmented rami. Inner seta on coxa large and pinnate in legs 1 and 2, but vestigial in legs 3 and 4. Outer seta on basis well-developed in leg 1, but rudimentary in legs 2–4. Inner distal spine on basis of leg 1 distinctly longer than first endopodal segment. Third exopodal segment of legs 2–4 about 3 times longer than wide, with straight, smooth inner margin. Armature formula for legs 1–4 as follows:

Leg 5 ( Fig. 73C ) protopod longer than wide, with naked outer distal seta; free exopodal segment about 2.9 times longer than wide (128×44 μm), armed with 1 small spineand 1 smallseta distally; ornamented with4 transverse rows of spinules on medial side.

Description of male. Body ( Fig. 73D ) 1.38 mm long. Urosome ( Fig. 73E ) 6-segmented. Fifthpedigerous somite short, obscurely defined from fourth pedigerous somite. Genital and 4 freeabdominal somites 124×174, 146×146, 118×118, 83×79, and 31×70 μm, respectively. Caudal ramus about 3.7 times longer than wide (81×22 μm).

Rostrum as in female. Antennule with first and second segments less expanded than in female. Antenna and mouthparts as in female.

Leg 1 as in female. Two distal setae on third endopodal segment of legs 2–4 short and spiniform ( Fig. 73F, G ). Inner seta on coxa well-developed and pinnate in legs 1–3, but rudimentary in leg 4. Inner setaon first exopodal segment present in legs 1–4, although small in legs 3 and 4 ( Fig. 73G, H ). Inner seta absent on second exopodal segment of legs 3 and 4. Armature formula for legs 2–4 as follows:

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

Leg 5 ( Fig. 73I ) protopod wider than long; free exopodal segment 59×20 μm, ornamented with 5 rows of spinules on inner surface. Leg 6 ( Fig. 73E ) represented by 2 smallsetae on distal margin of genital operculum.

Remarks. This species was previously known only from the western Atlantic. The above description is based on specimens from Pyura styeliformis collected at Palau in the Pacific. The Palau specimens were compared with the specimens from Microcosmus exasperatus collected at Guadeloupe in the West Indies. The two populations exhibited no significant morphological differences, although Monniot (1986) recorded the existence of some variability in P. macer . Pachypygus macer has a characteristic form of brood pouch and the 2-segmented endopod of the antenna serves to distinguish it from the typespecies, P. gibber .

Figures

FIGURE 71. Pachypygus macer Illg, 1958, female. A, habitus, right; B, urosome, ventral; C, distal part of abdomen, ventral; D, distal part of abdomen, left; E, antennule; F, antenna; G, labrum; H, mandible; I, maxilliped. Scale bars: A, 0.5 mm; B, 0.1 mm; C–I, 0.05 mm.

FIGURE 72. Pachypygus macer Illg, 1958, female.A, maxillule; B, maxilla; C, leg 1; D, leg 2; E, leg 3; F, leg 4. Scale bars: 0.05 mm.

FIGURE 73. Pachypygus macer Illg, 1958, female: A, rostrum; B, paragnath; C, leg 5. Male: D, habitus, left; E, urosome, ventral; F, leg 2; G, leg 3; H, exopod of leg 4; I, leg 5. Scale bars: A–C, 0.05 mm; D, 0.2 mm; E, 0.1 mm; F–I, 0.02 mm.