Demoixys cornuta, 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 : 551-554

Demoixys cornuta sp. nov.

( Figs. 369 , 370 )

Typematerial. Holotype (intact ♀, MNHN-IU-2014- 21409 ) , paratypes (2 intact ♀♀, MNHN-IU-2014- 21410), and dissected paratypes (3 ♀♀, figured) from Pseudodistoma arborescens Millar, 1967 (MNHN-IT-2018-11 = MNHNA 1/ PSE /80), ATIMOVATAE TA 28, Banc Tozer, Madagascar (25°12 Ś, 44°08 É), depth 20-22 m, MNHN coll., 25 May 2010.

Etymology. The specific name is derived from the Latin cornut (=horned), referring to the possession by the new species of the posterolateral horn-like processes on the dorsal cephalic shield.

Descriptionoffemale. Body ( Fig. 369A ) stout, inflated; body length 1.65 mm. Cephalosome indistinctly defined from metasome, dorsal cephalic shield with paired posterolateral horn-like processes; each process ( Fig. 369D ) sclerotized, bent dorsally in middle and with pointed tip. Metasome gradually broadening posteriorly, longer than wide, unsegmented, but with 2 constrictions delimiting first to third pedigerous somites. Free urosome ( Fig. 369B ) small, slightly shorter than wide, 2-segmented, consisting of genital complex and unsegmented abdomen. Genital complex subdivided by lateral constriction. Caudal rami ( Fig. 369C ) rudimentary, lobate, fused with abdomen; armedwith few minute setal vestiges distally.

Rostrum ( Fig. 369F ) large, elongate, extending to middle of labrum ( Fig. 369E ). Antennule ( Fig. 369G ) small, strongly tapering, 5-segmented; first to fifth segments armed with 0, 1, 2, 1, and 3 minute setae, respectively; terminal segment with several setules in addition to setae. Antenna ( Fig. 369H ) 3-segmented, consistingof coxa, basis, and unsegmented endopod; coxa and basis unarmed; endopod distinctly narrower and shorter than basis and 2.1 times longer than wide (38×18 μm); armed with 1 small seta distally plus small terminal claw bearing minute spinules distally.

Labrum ( Fig. 369I ) as simple, smooth and convex plate. Mandible ( Fig. 369J ) consistingof coxa and palp: coxal gnathobase with broad medial margin bearing 5 teeth distally and with pectinate proximal part (second and fourth teeth smaller than other 3); proximal corner of gnathobase acutely pointed: palp reduced, consisting of basis and small 1-segmented rami; basis with 1 small setaat mediodistal corner; exopod wider than long, incompletely articulated from basis, armed with 2 short setae distally; endopod as long as wide, with 2 small distal setae. Maxillule ( Fig. 369K ) extremely simplified and indistinctly bilobed, lobes with 1 seta and 5 setae (3 distal and 2 outer). Maxilla ( Fig. 369I ) 3-segmented; syncoxa bearing 2 small setae; basis with large, highly sclerotized claw only; endopod small, knob-like with 3 small setae. Maxilliped ( Fig. 369M ) lobate, bearing 2 smallsetae distally.

Legs 1–4 ( Fig. 370 A-D) biramous, with 2-segmented protopods; ornamented with few scattered setules; rami incompletely 2-segmented, except unsegmented endopod of leg 1, and obscurely articulated from basis. Endopods much smaller than exopods. Leg 1 exopod with 2 minute, papilliform rudiments of spines, one on outer distal corner on first exopodal segment and another on outer margin of second segment. Exopods of legs 2–4 armed with 5 small, spinulose spines, one on first segment and 4 on second. Coxa, basis, and endopod of all swimming legs unarmed.

Leg 5 ( Fig. 369B ) present on posteroventral surface of somite near base of urosome; represented by short, outer angular process and tapering, pointed inner process; both processes unarmed.

Male. Unknown.

Remarks. Based on the reduction in segmentation of the swimming leg rami and the general simplification of the mouthparts, combined with the retention of a welldeveloped, dentate coxal gnathobase on the mandible, this species is placed in the genus Demoixys . The new species can be readily distinguished from its congeners by its possession of a pair of posterolateral cephalic horns and by the extremely simplified mouthparts with, for example, the maxillule reduced to a bilobed vestige bearing a few setae.

Figures

FIGURE 369. Demoixys cornuta sp. nov., female. A, habitus, right; B, leg 5 and urosome, ventral; C, caudal rami, ventral; D, cephalic horn; E, anterior part of prosome, ventral; F, rostrum, left; G, antennule; H, antenna; I, labrum; J, mandible; K, maxillule; L, maxilla; M, maxilliped. Scale bars: A, 0.2 mm; B, E, F, 0.05 mm; C, D, G–M, 0.02 mm.

FIGURE 370. Demoixys cornuta sp. nov., female. A, leg 1; B, leg 2; C, leg 3; D, leg 4. Scale bars: 0.02 mm.