Doropygus depressus Stock, 1967

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 : 382-385

Doropygus depressus Stock, 1967

( Figs. 253 , 254 )

Material examined. 20 ♀♀ (MNHN-IU-2018-1874) and 1 dissected ♀ from Herdmania momus (Savigny, 1816) , Muscat, Gulf of Oman; 12 ♀♀ (MNHN-IU-2018-1875) and 2 dissected ♀♀ (figured) from Herdmania coutieri Monniot C., 2002 , Bahrain (26°12.47 Ń, 50°58.14 É) depth 5 m, 25 October 1994.

Description of female. Body ( Fig. 253A, B ) extremely dorsoventrally flattened: body length 1.74 mm. Prosome 1.62 mm, 4-segmented, consistingof cephalothorax and second to fourth pedigerous somites well defined by lateral constrictions, but dorsal suture lines faint. Cephalothorax 363×467 μm, more depressed than metasome. Second and third pedigerous somites 178×480 and 185×480 μm, respectively. Fouth pedigerous somite forming elongate brood pouch, 889×548 μm, 1.62 times longerthan wide; brood pouch concealing most of urosome in dorsal view, with only tips of caudal rami visible. Fifth pedigerous somite not articulated from fourth, expanded posterodorsally. Urosome ( Fig. 253C ) slender, gradually narrowing towards posterior end, indistinctly 6-segmented: genitalsomite 94×150 μm; 4 abdominalsomites 120×113, 130×107, 107×89, and 91×79 μm, respectively. Anal somite slightly narrowing posteriorly, with deep posteromedian incision. Caudal rami ( Fig. 253C ) divergent, elongate; each ramus about 7.9 timeslongerthan wide (204×26 μm) and about 2.2 times longer than anal somite; armed with 6 thin setae, 2 proximal setae positioned at 23 and 72% of ramus length.

Coxa Basis Exopod			Endopod
Leg 1 0-1 Legs 2 & 30-1 Leg 4 0-1	1-I 1-0 1-0	I-1; I-1; III, I, 4 1-1; 1-1; 3, 1, 5 1-0; 1-1; 2, 1, 5	0-1; 0-1; 1, 2, 3 0-1; 1, 3, 3 0-1; 1, 3, 2

Rostrum ( Fig. 254A ) triangular withrounded apex. Antennule ( Fig. 253D ) slender, 360 μmlong, aslongas cephalothorax, and 9-segmented; armatureformula 3, 14, 6, 3, 4, 4, 2, 2+aesthetasc, and 7+aesthetasc; 2 pinnate setae on first segment and 1 on sixth. Antenna ( Fig. 253E ) slender and 4-segmented; coxal and basis unarmed; first endopodal segment with 1 small seta subdistally; compound distal endopodal segment about 5.6 times longer than wide (111×20 μm); armed with about 7 small setae plus small terminal claw, about 0.3 times as long as segment.

Labrum with shallow posteromedian lobe; posterior margin with setules on both sides. Mandible ( Fig. 253F ) with 5 teeth, 1 subsidiary tooth on distal side of distalmost tooth, and 1 small proximal seta on coxal gnathobase: basis with 1 large setasubdistally on medial margin; exopod with 5 equally large setae; endopod 2-segmented; first segment with 4 setae on medial margin and several spinules on outer distal corner; second segment with 10 setae, 5 on medial and 5 on distal margins, and fine spinules along outer margin. Maxillule ( Fig. 254B ) armed with 9 setae on arthrite, 1 on coxal endite, 2 on coxal epipodite, 3 on basis, 4 on exopod, and 2 on endopod; proximal setaon basis shorter than distal 2 setae; 4 setae on exopod increasing in length from medial to outer. Maxilla ( Fig. 254C ) armedwith 9 setaeonsyncoxa (arranged as 3, 1, 2, and 3), 3 on basis, and 1, 1, and 4 on first to third endopodal segments. Maxilliped ( Fig. 254D ) unsegmented but with short trace of suture subdistally on medial side; armedwith 9 medial and 2 large apical setae.

Leg 1 ( Fig. 254E ) with 3-segmented rami. Outer seta on basis broad proximally and flagellate distally. Inner distal spine on basis robust, smooth, extending to distal border of first endopodal segment. First exopodal segment much broader than distal segments; outer spine large, extending to base of first outer spine of third exopodal segment. Legs 2–4 with 3-segmented exopods and 2-segmented endopods ( Fig. 254F, G ). Inner coxal seta large in legs 2 and 3, but rudimentary in leg 4. Outer seta on basis small and naked in legs 2–4. Most setae on legs 2 and 3, and all setae on leg 4 naked, except 2 inner proximal setae on both rami of legs 2 and 3. Second endopodal segment of legs 2 and 3 armed with 7 setae, that of leg 4 with 6 setae. First exopodal segment of leg 4 lacking inner seta; endopod of leg 4 slender. Armature formula for legs 1–4 as follows:

Leg 5 ( Fig. 253G ) rather small: protopod with small seta at outer distal corner; free exopodal segment gradually narrowing distally, 3.5 times longer than wide (53×22 μm), armeddistally with 2 setae(17 and 33 μm long), ornamented with 3 rows on minute spinules on dorsomedial surface.

Male. Unknown.

Remarks. As Stock (1967) mentioned in his original description, the habitus of this species is very unusual in having an extremely flattened prosome. His description regarding the armature of the mandible, maxillule, and maxilliped is revised in the above redescription. One of the two samples we examined was obtained from the type host, Herdmania momus collected in the Gulf of Oman, not far from the type locality in the Red Sea

Group D (maxillae with 3 setae on exopod and 2 setae on endopod)

Figures

FIGURE 253. Doropygus depressus Stock, 1967, female. A, habitus, dorsal; B, habitus, left; C, urosome, ventral; D, antennule; E, antenna; F, mandible; G, leg 5. Scale bars: A, B, 0.2 mm; C, 0.1 mm; D–F, 0.05 mm; G, 0.02 mm.

FIGURE 254. Doropygus depressus Stock, 1967, female. A, rostrum; B, maxillule; C, maxilla; D, maxilliped; E, leg 1; F, leg 2; G, leg 4. Scale bars: A, 0.1 mm; B–D, 0.02 mm; E–G, 0.05 mm.