Doropygusreticulatus, Kim & Boxshall, 2020

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 : 326-329

Doropygusreticulatus sp. nov.

( Figs. 216 , 217 )

Type material. Holotype ♀ (dissected and mounted on a slide, MNHN-IU-2014-21308 ) and paratype ♀ (dissected and mounted on a slide, MNHN-IU-2014-21309) from Pyura arenosa (Herdman, 1881) (MNHN-IT-2008-7399 = MNHNS 2/ PUY /484), CRRF 0 PHG 1713-U, Vietnam (08°41.12 Ń, 106°36.80 É), depth 0-1 m, 29 July 2008.

Etymology. The specific name refers to the surface reticulation on the exoskeleton of the prosomites.

Descriptionoffemale. Body ( Fig. 216A ) clearly segmented, length 3.04 mm; with thick, rigid exoskeleton. External surface of all prosomal somites reticulate, with polygonal sculpturing ( Fig. 216E ). Cephalosome and first to third pedigerous somites dorsoventrally depressed. Posterolateral corners of dorsal cephalic shield extended posteriorlybeyond distalborder offirst pedigerous somite; corners angular in dorsal view ( Fig. 216B ), but tapering and pointed in lateral view. First pedigerous somite small ( Fig. 216B ), half as wide as cephalic shield. Second to fourth pedigerous somites each with well-developed epimera. Cephalic shield and epimera of second to fourth pedigeroussomites thickened laterally, ornamented with minute surface granulation along lateral margins. Posterodorsal margins of second and third pedigerous somites concave and fringed with surface granulation. Fourth pedigerous somite expanded to form nearly oval brood pouch, longer than cephalosome plus anterior pedigerous somites combined, its epimera confined to anterior 20% of somite length, near base of leg 4. Freeurosome ( Fig. 216C ) slender, 5-segmented, with thick exoskeleton and surface granulation (not shown in Fig. 216C , but visible in Fig. 216A ). Genital somite 192×269 μm, narrow in posterior half. Four abdominal somites 212×269, 231×223, 173×188, and 138×150 μm, respectively, with first to third abdominal somites expanded posteriorly. Caudal ramus ( Fig. 216D ) slender, slightly archedventrally, about 7.4 timeslongerthan wide (340×46 μm) and about 2.5 times longer than anal somite; carrying vestiges of 6 setae, 2 proximal setae located at 27 and 64% of ramus length.

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

Rostrum represented by broad, blunt apical lobe of cephalosome. Antennule ( Fig. 216F ) slender and 9- segmented; setae strongly entangled, not countable. Antenna ( Fig. 216G ) slender, 4-segmented; coxa short and unarmed; basis 99×53 μm, with 1 smallseta distally; first endopodal segment 83×50 μm, with 1 small seta on inner margin; compound distal endopodal segment 5.2 times longer than wide (162×31 μm) and twice as long as first endopodal segment, ornamented with 2 groups of minute spinules on outer margin; armed with 10 small setae plus small terminal claw, about one-third as long as segment.

Labrum ( Fig. 216H ) with smooth sides, strongly tapering to narrow, linear free posterior margin, with small posteromedial lobe. Mandible ( Fig. 216I ) with 5 major teeth, 1 distalsubsidiarytooth, and 2 smallproximal setae on coxal gnathobase; basis with 1 seta on medial margin; exopod with 5 setae, distal outer seta slightly shorter than other 4; first endopodal segment bearing 4 setae and spinules near outer distal and medioventral surfaces; second endopodal segment with 9 setae and spinules on outer margin. Maxillule ( Fig. 216J ) with 9 setae on arthrite, 1 on coxal endite, 2 on epipodite, 3 on basis, 4 onexopodand 3 on endopod. Maxilla ( Fig. 217A ) 5-segmented; syncoxawith 9 setae (grouped as 3, 1, 2, and 3); basiswith 3 setae; endopodwith 1, 1, and 4 setae on first to third segments, respectively. Maxilliped ( Fig. 217B ) unsegmented, elongate, armedwith 9 setae on medial margin and 2 subequal setae apically.

Leg 1 ( Fig. 217C ) with 3-segmented rami. Inner coxal seta broadened and highly sclerotized in proximal part, extending beyond tip of inner distal spine on basis. Outer seta ( Fig. 217D ) on basis spiniform, constricted proximally and in distal third, with slender flagellate tip. Inner distal spine on basis extending to middle of third endopodal segment, curved, spinulose along distal half. Outer spine on first exopodal segment large, twice as long as outer spine on second segment.

Legs 2–4 with 3-segmented exopods and 2- segmented endopods ( Fig. 217E, F ); endopods distinctly longer than exopods. Legs 2 and 3 with same setation. Inner coxal seta elongate, much longer than endopod. Outersetaonbasis rudimentary, scarcely visible. Outer setae on exopods longerthan ramus. Proximal 2 inner setae on endopod of leg 4 shorter than other endopodal setae. Second endopodal segment of legs 2–4 elongated, with uneven lateral margins. Second endopodal segment of leg 4 longerthan exopod. First exopodal segment of leg 4 lacking inner seta. Armature formula for legs 1–4 as follows:

Leg 5 ( Fig. 217G ) 2-segmented: protopod short, with several spinules near base of exopod and 1 outer distal seta (this seta missing in observed specimens); free exopodal segment slender, graduallynarrowing distally, 4.5 times longer than wide (126×28 μm), with 2 long setae distally (outer seta 140 μm long, inner 103 μm) and 4 rows of spinules on dorsomedial surface.

Male. Unknown.

Remarks. In the genus Doropygus there are ten species currently known to have a maxillule combining the presence of 4 setae on the exopod with 3 setae on the endopod, as found in D. reticulatus sp. nov. Among these species, D. rigidus Ooishi, 1962 and probably D. platythorax Jones, 1974 have, like the new species, a highly sclerotized, rigid exoskeleton but the surface reticulationof the prosomites, as found in the newspecies, has not been reported in any of those ten species.

These ten species typically have elongate caudal rami and three are known to have caudal rami which are more than 6 times as long as wide, as in D. reticulatus sp. nov. These three species are D. kerguelensis , D. platythorax , and D. rigidus . However, all three of these species have a much broader free exopodal segment of leg 5, which is up to 3.5 times as long as wide in contrast to 4.5 times in D. reticulatus sp. nov. In two other species, D. spiniferus Schellenberg, 1922 and D. trisetosus Schellenberg, 1922 the information available on their caudal rami is incomplete but it is reported that in both species the caudalramus is 1.5 timeslongerthan the anal somite. Fortunately, Doropygus reticulatus sp. nov. is readily distinguishable from these two species because its caudal ramus is 2.5 times longer than the anal somite.

The characteristic shape of the outer seta on the basis of leg 1 may be a diagnostic feature of D. reticulatus sp. nov. allowing it to be differentiated from its congeners.

Figures

FIGURE 216. Doropygus reticulatus sp. nov., female. A, habitus, right; B, anterior part of prosome, dorsal; C, urosome, ventral; D, right caudal ramus, lateral; E, dorsal reticulation on surface of prosome; F, antennule, setal armature omitted; G, antenna; H, labrum; I, mandible; J, maxillule. Scale bars: A, 0.5 mm; B, C, 0.2 mm; D, 0.1 mm; E–H, J, 0.05 mm; I, 0.02 mm.

FIGURE 217. Doropygus reticulatus sp. nov., female.A, maxilla; B, maxilliped; C, leg 1; D, outer seta on basis of leg 1; E, leg 2; F, leg 4; G, leg 5. Scale bars: A–C, E–G, 0.05 mm; D, 0.02 mm.