Doropygus pulex Thorell, 1859

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 : 353-357

Doropygus pulex Thorell, 1859

( Figs. 234 , 235 )

Material examined. 4 ♀♀ (MNHN-IU-2018-1854) and 2 dissected ♀♀ from Ascidiella aspersa (M̹ller, 1776), Porto Vecchio, Corsica, 1987; 8 ♀♀ (MNHN-IU-2018- 1855) and 3 dissected ♀♀ from A. aspersa, Etang de Leucate , Mediterranean coast of France, collected by Clanzig, 1985.

5 ♀♀ (MNHN-IU-2018-1856) and 1 dissected ♀ from Polycarpa pomaria (Savigny, 1816) off Banyuls, Mediterranean coast of France, depth 300 m; 15 ♀♀ (MNHN-II-2018-1857) from P. pomaria off Banyuls; 58 ♀♀, 8 ♂♂ (MNHN-IU-1858) from P. pomaria, Kristineberg , Sweden, 1962.

1 ♀ (MNHN-IU-2018-1859) and 1 dissected ♀ from Ascidia mentula Müller, 1776 , Bergen, Norway; 2 ♀♀ (MNHN-IU-2018-1860) from A. mentula Kristineberg , Sweden.

54 ♀♀ (MNHN-IU-2018-1861) and 2 dissected ♀♀ from Microcosmus sabatieri Roule, 1885 , Bonifacio, Corsica.

26 ♀♀, 12 ♂♂ (MNHN-IU-2009-5194) and 1 dissected ♀ from Pyura dura (Heller, 1877) Marina de Fiori , Porto Vecchio, Corsica, 1992

2 ♀♀ (MNHN-IU-2018-1862) and 1 dissected ♀ from Pyura squamulosa (Alder, 1863) , trawl, Banyuls.

49 ♀♀, 6 ♂♂ ((MNHN-IU-2009-5192) and 1 dissected ♀ from Pyura tessellata (Forbes, 1848) Marina di Fiori Creek , Porto Vecchio, Corsica

Supplementary description of female (from Ascidiella aspersa ). Body ( Fig. 234A ) slightly compressed laterally, 2.90 mmlong. Prosome 2.27 mm long, distinctly 5-segmented. Dorsalcephalic shield large. Fourth pedigeroussomite forming elliptical brood pouch widest in middle, 1.09×0.77 μm in lateral view, tapering posteriorly towards rounded apex. Free urosome ( Fig. 234B ) slender, cylindrical, 5-segmented: genitalsomite 159×295 μm, distinctly wider than long; 4 abdominal somites wider than long, 218×255, 205×250, 159×245, and 159×255 μm, respectively. Anal somite broadened posteriorly, with deep posteromedian incision. Caudal rami divergent; each ramus ( Fig. 234C ) about 4.1 times longer than wide (276×67 μm) and about 1.7 times longer than anal somite, gradually narrowing distally towards unsclerotized, weak distal third: armed with 6 rudimentary setae; lateral and dorsal setae located at 25 and 58% of ramus length, respectively.

Rostrum ( Fig. 234D ) unsclerotized, flexible, longer than wide (89×73 μm), weakly tapering towards rounded or bluntly nipple-shaped apex. Antennule ( Fig. 234E ) 280 μm long, 9-segmented withdistal 3 segments incompletely articulated; armatureformula 3, 17, 6, 4+aesthetasc, 3, 2+aesthetasc, 2, 2+aesthetasc, and 7+aesthetasc; setae generally small, all naked. Antenna ( Fig. 234F ) 4- segmented, coxa short; basis 85×50 μm, with 1 smallseta distally and 1 vestigial seta subdistally on outer margin; first endopodal segment 67×42 μm, with 1 smallseta subdistally; compound distal endopodal segment 3.2 timeslongerthan wide (83×26 μm); armedwith 6 setae (2 of distal 3 setae indistinct) plus large terminal claw, 72 μm long, 0.87 times as long as segment.

	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		1-0	1-1; 1-1; 3, 1, 5	0-1; 1, 3, 4
Leg 4	0-1	1-0	1-1; 1-1; 2, 1, 5	0-1; 1, 3, 3

Labrum ( Fig. 234G ) with setulose distal margin and sparsely setulose, linguiform posteromedian lobe. Mandible ( Fig. 234H ) with 5 teeth on coxalgnathobase and 2 small proximal setae; sharply pointed distalmost tooth with minute spinules along proximal margin: basis with 1 subdistal seta on medial margin; exopod 4- segmented with 4 large setae of equal length; endopod incompletely articulated from basis and 2-segmented; first segment armed with 3 or 4 setae and ornamented with oblique mediodistal row of spinules on ventral surface; second segment armed with 8 or 9 setae, second outer distal seta longest, more than twice as long as outermost distal seta and about 1.2 times longer than second longest (third outer distal seta). Setation of first and second segments of mandibular endopod variable in 6 dissected specimens: 3-8, 3-8, 4-8, 4-9, and 4-9, with no variation between left and right mandibles in 5 specimens, but 4-8 on right mandible and 4-9 on left mandible in 1 specimen. Paragnath ( Fig. 234I ) with semicircular, sclerotized outer lobule subdistally, few minute spinules apically, and setules along medial margin. Maxillule ( Fig. 234J ) with 9 setae on arthrite; coxal endite bearing broad seta (wider than long) with pointed tip; epipodite with 2 very unequal setae; basis with 3 setae on medial margin; exopod with 4 setae on distal margin (3 medial setae equal in length, outermost seta 1.5 times longer than other 3); endopod smaller than exopod, with 2 subequal setae. Maxilla ( Fig. 235A ) 5-segmented; syncoxawith 3, 1, 2, and 3 setaeon first to fourth endites, respectively; basis with 3 setae, distalmost about half as long as middle seta; endopod with 1, 1, and 3 setae on first to third segments, respectively. Maxilliped ( Fig. 235B ) incompletely 2-segmented; first segment with 9 setae; short second segment with 2 large, subequal setae.

Leg 1 ( Fig. 235C ) biramous with 3-segmented rami. Inner coxal seta extending at most to distal border of second endopodal segment; outer seta on basis with flagellate tip and several setules distally. Inner distal spine on basis 55 μm long, extending to distal border of first endopodal segment, finely spinulose distally. Outer spines on exopod slender, flanged with membrane distally.

Legs 2–4 with3-segmented exopodsand 2-segmented endopods ( Fig. 235D, E ); exopod and endopod similar in length in legs 2 and 3, but exopod slightly longer than endopod in leg 4. Inner coxal seta extending to middle of compound distal endopodal segment in legs 2 and 3, but that of leg 4 small and naked, extending to distal border of basis. Outersetaonbasis rudimentary, hardly visible. Most of setae on exopods and distal setae on endopods finely spinulose distally. Two proximal setae on endopod and inner seta on first exopodal segment of leg 4 short. Armature formula for legs 1–4 as follows:

Leg 5( Fig. 235F ) consistingof protopodnotarticulated at base, armed with vestigial seta at outer subdistal region androw of about 15 spinulesat mediodistalcorner, plus free exopodal segment, about 2.5 timeslongerthan wide, with rounded outer distal corner; armed distally with 1 short, broad seta and 1 longer thread-like seta; ornamented with 3 oblique rows of fine spinules on dorsomedial surface.

Male. Not examined.

Remarks. Doropygus pulex is the type species of the genus but has been rather poorly defined. According to both Lang (1948) and Gotto (1975), it is likely that more than one species has been referred to D. pulex . Gotto (1975) recognized that there are different taxa within the D. pulex complex, which differ in the number of setae on the secondendopodal segment of the mandible (8 or 9) and in the relative size of the terminal claw of the antenna (small or at least half as long as the compound distal endopodal segment).

In his original description of D. pulex, Thorell (1859) listed five species of ascidians as type hosts, as follows: Ascidia virginea M̹ller, 1776 (as A. venosa ), Ascidiella aspersa (as Ascidia aspersa ), Ciona intestinalis (as Ascidia canina ), Corella parallelogramma (as Ascidia parallelogramma ), and “ Cynthia lurida ” (an invalid name according to WoRMS). Copepods belonging to the D. pulex complex from one of the above type hosts, Ascidiella aspersa , were available to us for a study. The body form of the examined specimens from A. aspersa is very similar to that illustrated by Thorell (1859) and the antenna bears a large terminal claw, as in the illustration given by Thorell. Thorell’s illustration of the mandible shows the exopod bearing 4 large setae of equal length but the secondendopodal segment bears only 7 setae. We consideritlikelythat heoverlookedthemediodistalsetaon the second endopodal segment; this seta is prone to being overlooked because itis small, positioneddorsally (so not in the same plane as the other setae) and is overlapped by a larger adjacent seta. We infer, therefore, that the typical setation of the mandibular endopod of D. pulex s. str. is 3 or 4 (4 is common) on the first segment and 8 or 9 (8 is common) on the second segment. Considering these attributes, we conclude that the copepod material from one of the type hosts ( A. aspersa ) described above can be identified as D. pulex s. str. with a high degree of confidence. We also suspect that the variability in setation on the mandibular endopod might have been the root cause of the earlier confusion surrounding the diagnosis of D. pulex .

The features of the specimens from Polycarpa pomaria conform well with those of the specimens from A. aspersa . However, material examined here from six other species of ascidians cannot be separated into robust groupings due to variability, especially in the shape of the brood pouch and the proportions of the caudal rami. We note that all lie within the following ranges of character states: (1) The caudal rami are between 4.1 and 6.3 times longer than wide, and 1.7 to 2.5 times longerthan the anal somite; (2) the compound distal endopodal segment of the antenna is 3.0 to 3.8 times longer than wide; (3) the terminal claw of the antenna is 0.55 to 0.9 times as long as the distal endopodal segment; (4) the mandibular exopod is armed with 4 equally large setae; (5) the first segment of the mandibular endopod is armed with 3 or 4 setae and ornamented with one oblique row of spinules; (6) the second segment of the mandibular endopod is armed with 8 or 9 setae; (7) the maxillular exopod and endopod are armed with 4 and 2 setae, respectively, and the seta on the coxal endite is broad and up to twice as long as wide; (8) in the maxilla, the first endite of the syncoxa and the terminal segment of the endopod are armed with 3 setae, and the basis is armed with 3 setae (lacking a differentiated claw); (9) the maxilliped is incompletely 2- segmented and armed with 9 setae on the first segment and 2 setae on the second segment; (10) the outer seta on the basis of leg 1 is cylindrical proximally and has a flagellate distal tip; and (11) the exopodal segment of leg 5 is about 2.4 times longer than wide. This general set of character states serves to define D. pulex s. str. but we consider that it will be necessary in the future to use molecular data to fully explore the limits to such variation and establish robust species boundaries.

Figures

FIGURE 234. Doropygus pulex Thorell, 1859, female. A, habitus, right; B, urosome, ventral; C, left caudal ramus, dorsal; D, rostrum; E, antennule; F, antenna; G, labrum; H, mandible; I, paragnath; J, maxillule, Scale bars: A, 0.5 mm; B, 0.2 mm; C, 0.1 mm; D–J, 0.05 mm.

FIGURE 235. Doropygus pulex Thorell, 1859, female. A, maxilla; B, maxilliped; C, leg 1; D, leg 2; E, leg 4; F, leg 5. Scale bars: A, B, F, 0.05 mm; C–E, 0.1 mm.