Mecodelphys edentatus, 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 : 572-574

Mecodelphys edentatus gen. et sp. nov.

( Figs. 383 , 384 )

Typematerial. Holotype (intact ♀, MNHN-IU-2014- 21419 ) , paratypes (6 intact ♀♀, MNHN-IU-2014-21420), and dissected paratypes (2 ♀♀, figured) from the colonial ascidian Lissoclinum taratara Monniot C. & Monniot F., 1987 (MNHN-IT-2008-4990 = MNHNA 2/ LIS /162), CRRFCRCHO 297, Cape Rodney Pass, Papua New Guinea (10°15.66 Ś, 148°22.27 É), depth 31 m, 11 June 1998.

Etymology. The name is from the Latin e (=without) and dentat (=toothed), alluding to the absence of a coxal gnathobase in the new species.

Descriptionoffemale. Body( Fig.383A ) Doropygus - like in form, surface ornamented with numerous, minute setules. Prosome divisible by weak constrictions into cephalosome, first and second pedigerous somites, and fused third and fourth pedigerous somites; dorsal cephalic shield expanded ventrolaterally, bearing pair of small, acutely pointed, spiniform processes posterolaterally ( Fig. 383C ). Fused third and fourth pedigerous somites swollen, forming brood pouch. Free urosome ( Fig. 383B ) 5- segmented: genital somite short, only partially articulated from brood pouch; 4 abdominal somites setulose, 85×144, 69×131, 38×118, and 80×107 μm, respectively. Caudal ramus ( Fig. 383D ) tapering, covered with setules, about 2.7 timeslongerthan wide (75×28 μm), slightly shorter than anal somite, tipped with short, spiniform process: armedwith 5 smallsetae (2 outer lateral, 1 outer subdistal, and 2 small distal).

Rostrum ( Fig. 383E ) rather large, 100×89 μm, evenly tapering towards pointed apex, surface covered with setules. Antennule ( Fig. 383F ) stout, 148 μm long, covered with setules, unsegmented but with 2 partial articulations on posterior surface; armed with about 17 small setae. Antenna ( Fig. 383G ) slender and 3- segmented; coxashortand unarmed; secondsegment (fused basis and first endopodal segment) also unarmed, with vestige of articulation near middle; third segment (second endopodal segment) about 4.2 timeslongerthan wide (101×24 μm); armed with 4 tiny setae (1 proximal, 2 subdistal, and 1 distal) plus small terminal claw, about 0.2 times as long as segment.

Labrum ( Fig. 383H ) large with rounded posterior margin. Mandible consisting only of palp, without coxal gnathobase; palp unsegmented with lobate rami; inner lobe broad and blunt; each lobe armed with 4 naked setae. Maxillule ( Fig. 384A ), maxilla ( Fig. 384B ), and maxilliped( Fig. 384C )eachrepresentedby lobe.Maxillule narrowing distally, with subdistal constriction, armed with 4 equal setae on apex. Maxilla tipped with 1 short seta, and maxilliped with 1 longer seta. All mouthparts ornamented with scattered setules.

Legs 1–4 ( Fig. 384 D-G) biramous, with unsegmented protopods armedwith smallouter seta; both rami elongate, digitiform, fused with or incompletely articulated with protopod, covered with setules. Leg 1 distinctly smaller than posterior swimming legs. Endopods slightly longer than exopods in legs 1–3, but less than one-third as long as exopod in leg 4. Lengths of rami: 153, 258, 251, and 207 μm, respectively, for exopods of legs 1–4; and 167, 275, 285, and 64 μm, respectively, for endopods of leg 1-4. Endopods unarmed, but exopods of legs 1–4 armed with few, small setae distally, 2 or 3, 1, 2, and 3, respectively.

Leg 5 ( Fig. 384H ) represented by 2 ventral processes on each side of somite; outer protopodal process tipped with 1 seta; inner exopodal process conical, pointed apically, bearing 1 seta on its outer margin.

Male. Unknown.

Remarks. The caudal ramus of M. edentatus gen. et sp. nov. bears 5 smallsetae and a claw-like distal process. It can be inferred that the latter process is derived from the fusion of a seta to the ramus.

Figures

FIGURE 383. Mecodelphys edentatus gen. et sp. nov., female. A, habitus, right; B, urosome, ventral; C, anterior part of prosome, right side view showing posterolateral process on dorsal cephalic shield (arrowhead); D, left caudal ramus, dorsal; E, rostrum; F, antennule; G, antenna; H, labrum and mouthparts; I, mandible. Scale bars: A, 0.2 mm; B, C, 0.1 mm; D, F, I, 0.02 mm; E, G, H, 0.05 mm.

FIGURE 384. Mecodelphys edentatus gen. et sp. nov., female. A, maxillule; B, maxilla; C, maxilliped; D, leg 1; E, leg 2; F, leg 3; G, leg 4; H, left leg 5, ventral. Scale bars: A–C, 0.01 mm; D–G, 0.05 mm; H, 0.02 mm.