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

publication ID

https://doi.org/ 10.11646/megataxa.4.1.1

DOI

https://doi.org/10.5281/zenodo.6422139

persistent identifier

https://treatment.plazi.org/id/03C487CB-ED4E-3817-FCEF-F98FFE57FD26

treatment provided by

Plazi

scientific name

Ctenixys pusilla
status

gen. et sp. nov.

Ctenixys pusilla gen. et sp. nov.

( Figs. 363 View FIGURE 363 , 364 View FIGURE 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 View FIGURE 363 ) 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 View FIGURE 363 ) 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 View FIGURE 363 ) 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 View FIGURE 363 ) semicircular, 1.5 times wider than long, setulose. Antennule ( Fig. 363E View FIGURE 363 ) 100 μmlong, setulose, broad, tapering, indistinctly 6-segmented; 2 distal articulations obscure; setae indistinguishable from setules. Antenna ( Fig. 363F View FIGURE 363 ) 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 View FIGURE 363 ) semicircular, with few setules. Mandible ( Fig. 363H View FIGURE 363 ) 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 View FIGURE 363 ) 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 View FIGURE 363 ) 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 View FIGURE 363 ) small, as unsegmented lobe armed distally with 4 or 5 (5 is common) naked setae.

Legs 1–4 ( Fig. 364 View FIGURE 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 View FIGURE 364 ) 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.

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