Notoixys ovata, 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 : 517-520

Notoixys ovata gen. et sp. nov.

( Figs. 344 , 345 )

Type material. Holotype ♀ (dissected and mounted on a slide, MNHN-IU-2014-21391 ) from Aplidium millari Monniot C. & Monniot F., 1994 (Type MNHN-IT-2008- 556 = MNHNA1/APL.B/295), EPOS 3 Stn 235, Weddell Sea, Antarctic Ocean (75°09.1’S, 27°34.7’W), depth 407 m, 31 January 1989.

Etymology. The name is derived from the Latin ovat (=egg-shaped), referring to the ovate prosome of the new species.

Descriptionoffemale. Body ( Fig. 344A ) straight, slightly depressed, 2.11 mm long. Prosome inflated, oval, 1.76 mm long: greatest width of prosome 1.25 mm, at posterior third. Cephalosome ( Fig. 344B ) short, defined from metasome; dorsal cephalic shield with paired lateral horn-like processes ( Fig. 344C ). Metasome lacking any trace of articulation. Free urosome ( Fig. 344D ) small, indistinctly 5-segmented; articulations between somites obscure, representedbyweakconstrictionsand faintsuture lines. Genital somite short, characteristically bearing short, broad hood-like flap of cuticle along posterodorsal margin ( Fig. 344B ). Caudalramus ( Fig. 344E ) small, shorter than anal somite and about 2.7 times longer than wide (82×31 μm), tapering in distal third, ornamented with several setules; caudal setae not distinguishable from setules.

Rostrum ( Fig. 344F ) well-developed, longer than wide, slightly tapering proximally and strongly taperingdistally towards angular apex. Antennule ( Fig. 344G ) tapering, 225 μmlong, indistinctly 8-segmented; armatureformula 2, 15, 7, 3, 2, 2, 2, and 7+aesthetasc; third segment subdivided; all setae small, setule-like. Antenna ( Fig. 344H ) 4-segmented; proximal 3 segments unarmed; terminal segment (second endopodal segment) 2.7 timeslongerthan wide (68×25 μm) and longerthan firstendopodal segment: armedwith 7 setae (arranged as 2, 2, and 3) plus terminal claw half as long as segment.

Labrum weak, easily damaged during dissection. Mandible ( Fig. 344I ) with 3 small teeth and short pectinate margin on coxal gnathobase: basis with broad setaon medial margin: exopod with 4 equally large setae and 1 short outer seta half as long as others: endopod with 1 and 6 setae on first and second segments, respectively. Maxillule ( Fig. 344J ) armedwith 6 setaeon arthrite, 1 on epipodite, 2 on basis, 4 onexopodand 3 on endopod; setae on endopod longer than those on exopod; coxal endite absent. Maxilla ( Fig. 344K ) 5-segmented; syncoxawith 3, 1, 2, and 2 setae on first to fourth endites, respectively; basis with short claw plus 2 unequal setae; endopod with 1, 1, and 2 setae on first to third segments, respectively. Maxilliped ( Fig. 344L ) as unsegmented, elongate lobe bearing 5 naked setae distally.

Legs 1–4 ( Fig. 345 A-D) with incompletely 3- segmented rami. Protopod obscurely segmented in legs 3 and 4. Endopods slightly shorter than exopods in legs 1 and 2, but distinctly shorter, half as long as exopod, in legs 3 and 4. Inner coxal seta present in legs 1 and 2, absent in legs 3 and 4. Setae on rami small, markedly smaller inlegs 3 and 4. First exopodal segments of legs 3 and 4 lacking inner seta. Second endopodal segment of leg 2 bearing 2 inner setae. Second endopodal segment of leg 3 lacking inner seta. Armature formula for legs 1–4 as follows:

	Coxa	Basis	Exopod	Endopod
Leg 1	0-1	1-1	1-1; 1-1; 7	0-1; 0-1; 6
Leg 2	0-1	1-0	1-1; 1-1; 8	0-1; 0-2; 6
Leg 3	0-0	1-0	1-0; 1-1; 8	0-1; 0-0; 6
Leg 4	0-0	1-0	1-0; 1-1; 7	0-1; 0-1; 3
Leg 5	absent.

Male. Unknown.

Remarks. Notoixys ovata gen. et sp. nov. can readily be differentiated from its congeners by the following features: the ovoid, slightly depressed body shape, the presence of the posterodorsal hood-like flap on the genital somite, the presence of only 2 setae on the third endopodal segment of the maxilla, the absence of leg 5, and the characteristic setation of legs 1–4.

The new species is superficially similar in body shape to Mesoixys otaria Illg & Dudley, 1965 , but the genus Mesoixys may distinguished from Notoixys gen. nov. (and other genera) by the styliform coxal gnathobase on the mandible and by the lack of the maxilliped.

Figures

FIGURE 344. Notoixys ovata gen. et sp. nov., female.A, habitus, ventral; B, cephalic region, dorsal; C, cephalic horn; D, urosome, dorsal; E, left caudal ramus, dorsal; F, rostrum; G, antennule; H, antenna; I, mandible; J, maxillule; K, maxilla; L, maxilliped. Scale bars: A, B, 0.5 mm; C, E–G, 0.05 mm; D, 0.1 mm; H–L, 0.02 mm.

FIGURE 345. Notoixys ovata gen. et sp. nov., female. A, leg 1; B, leg 2; C, leg 3; D, leg 4. Scale bars: A, B, 0.05 mm; C, D, 0.02 mm.