Ctenixys pusilla, 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 : 544-547

Ctenixys pusilla gen. et sp. nov.

( Figs. 363 , 364 )

Typematerial. Holotype (intact ♀, MNHN-IU-2014- 21405 ) , paratypes (7 intact ♀♀, MNHN-IU-2014-21406), and dissected paratypes (2 ♀♀, figured) from Diplosoma listerianum (Milne Edwards, 1841) (MNHN-IT-2008- 3541= MNHNA 2/ DIP.A/69), Îlot Canard, New Caledonia, depth 9 m, Monniot coll., 12 September 1985.

Etymology. The specific name is derived from the Latin pusill (=very small), referring to its small body.

Descriptionoffemale. Body ( Fig. 363A ) stout, inflated; bodylength 1.06 mm. Prosome 882 μmlong; dorsal cephalic shield well-defined, with very small horn-like process posterolaterally on each side. Metasome gradually broadening posteriorly towards rounded margin, unsegmented but with dorsal constriction between pedigerous regions of legs 1 and 2. Freeurosome ( Fig. 363B ) directed ventrally, perpendicular to prosomal axis, evenly tapering, 5-segmented; articulations between last 3 segments incomplete; surface of anal somite and caudal rami ornamented with setules. Caudal rami ( Fig. 363C ) short, obscurely defined from anal somite, slightly longer than wide (24×21 μm) and about half as long as anal somite, with rounded distal margin; caudal setae indistinguishable from setules.

Rostrum ( Fig. 363D ) semicircular, 1.5 times wider than long, setulose. Antennule ( Fig. 363E ) 100 μmlong, setulose, broad, tapering, indistinctly 6-segmented; 2 distal articulations obscure; setae indistinguishable from setules. Antenna ( Fig. 363F ) 3-segmented; coxa and basis unarmed; unsegmented endopod about 3.4 times longer than wide (55×16 μm) and as long as basis: armed with 5 setae (grouped as 1, 1, and 3) plus small terminal claw, aboutone-thirdaslongas endopod.

Labrum ( Fig. 363G ) semicircular, with few setules. Mandible ( Fig. 363H ) with elongate coxal gnathobase terminating in narrow, pectinate medial margin; basis with 1 seta medially; exopod with 4 longer medial setae and 1 short outer seta; first endopodal segment projecting medially and armed with 1 seta; second segment narrow, with 4 smallsetae. Maxillule ( Fig. 363I ) with 3 setae on arthrite and 1 seta on coxal epipodite; coxal endite absent; exopod and endopod both fused with basis but discernible from each other by marginal notches; regions representing basis, exopod and endopod armed with 1, 4, and 3 setae, respectively. Maxilla ( Fig. 363J ) 3-segmented, comprising syncoxa, basis, and unsegmented endopod; syncoxa bearing 2, 1, and 2 setae on first to third endites, respectively; basis armed only with strong claw bearing 2 rows of spinules distally; endopod small with 3 setae, smallest seta naked, all other setae on maxilla pinnate. Maxilliped ( Fig. 363K ) small, as unsegmented lobe armed distally with 4 or 5 (5 is common) naked setae.

Legs 1–4 ( Fig. 364 A–D) reduced in segmentation and setation; inner coxal seta absent. Leg 1 with incompletely 2-segmented rami; basis with large outer seta, but lacking inner distal element. Legs 2–4 with protopod (fused coxa and basis) bearing outer seta and incompletely 2-segmented exopod. Leg 2 endopod rudimentary, knob-like, tipped with 1 seta. Legs 3 and 4 lacking trace of endopod. Armature formula for legs 1–4 as follows:

	Protopod	Exopod	Endopod
Leg 1	1-0	1-0; 5	0-0; 5
Leg 2	1-0	1-0; 6	1
Leg 3	1-0	0-0; 6	absent
Leg 4	1-0	0-0; 5	absent

Leg 5 ( Fig. 364E ) represented by 2 unequal posteroventral lobes (smaller outer and larger inner) on somite, each tipped with 1 seta.

Male. Unknown.

Remarks. Ctenixys pusilla gen. et sp. nov. differs from its congenersin theabsence of an innerdistalelement on the basis of leg 1, in the absence of an endopod on leg 3 (cf. present in both other species), in the possession of fewer setae on the maxilliped (4 or 5, compared with 6 in C. abdominalis and 8 in C. affinis ), and in the different setation of legs 1 and 2.

Figures

FIGURE 363. Ctenixys pusilla gen. et sp. nov., female. A, habitus, right; B, leg 5 and urosome, ventral; C, caudal rami, dorsal; D, rostrum; E, antennule; F, antenna; G, labrum; H, mandible; I, maxillule; J, maxilla; K, maxilliped. Scale bars: A, 0.1 mm; B, 0.05 mm; C–J, 0.02 mm; K, 0.01 mm.

FIGURE 364. Ctenixys pusilla gen. et sp. nov., female. A, leg 1; B, leg 2; C, leg 3; D, leg 4; E, leg 5. Scale bars: 0.02 mm.