Ammonixysquadridens, 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 : 541-542

Ammonixysquadridens gen. etsp. nov.

( Figs. 361 , 362 )

Type material. Holotype ♀ (dissected and mounted on a slide, MNHN-IU-2014-21404 ) from Polyclinum isipingense Sluiter, 1898 (MNHN-IT-2008-XXX = MNHN A1/POL.B/108), ATIMOVATAE TR07, Madagascar (25°01 Ś, 47°00 É), depth 12-16 m, MNHN coll., 01 May 2010.

Etymology. The specific name is from the Latin quadr (=four) and dens (=tooth), referring to the presence of four teeth on the coxal gnathobase of the mandible.

Descriptionoffemale. Body ( Fig. 361A, B )globular, greatly swollen: body length 1.12 mm from frontal margin of cephalosome to posterior margin of fourth pedigerous somite. Prosome with smooth surface; lateral margins of dorsal cephalic shield expanded ventrally, completely concealing mouthparts in lateral view. Metasome 4- segmented; first and second articulations complete, third articulation incomplete; first to third pedigerous somites much wider than long, Fourth pedigerous somite greatly expanded, spherical, 785×774 μm. Freeurosome ( Fig. 361C ) small, stout, 5-segmented, inserted into ventral surface of brood pouch ( Fig. 361B ). All urosomites much widerthan long; 4 abdominal somitessparsely ornamented with minute spinules. Caudal ramus ( Fig. 361C ) small, lobate, slightly longerthan wide, not articulated from anal somite, bearing minute setules; caudal setae apparently absent.

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

Rostrum ( Fig. 361E ) distinct, slightly longerthan wide (84×72 μm), tapering to narrow apex. Antennule ( Fig. 361F ) archedposteriorly, 117 μmlong, 6-segmented; third and fourth segments articulated from each other only on one surface; first segment with 2 setae; setation of other segments obscure due to similarity with setules; third, fifth and terminal segments each bearing 1 small aesthetasc. Antenna ( Fig. 361G ) stout, 4-segmented; coxa, basis, and first endopodal segment unarmed; basis shorter than first endopodal segment; narrower second endopodal segment about 2.3 times longer than wide (41×18 μm) and as long as first segment: armed with 3 small setae plus small terminal claw, about one-third as long as second endopodal segment.

Labrum ( Fig. 361H ) simple, unornamented, with short,broadposteromedian lobe.Mandible ( Fig.361I ) with coxal gnathobase bearing 4 teeth on distal half of medial margin and pectinate proximal half of medial margin: palp consisting of basis and 2-segmented endopod; basis with 1 seta mediodistally; exopod completely fused with basis, represented by outer lobe of basis and pair of large setae at base of lobe; endopod 2-segmented, incompletely articulated from basis, with 1 broad seta on first segment and 4 setaeon second. Maxillule ( Fig. 362A ) armedwith 6 setae on arthrite, 1 on coxal epipodite, 1 on basis, 4 on exopod and 3 on endopod; coxal endite absent. Maxilla ( Fig. 362B ) 4-segmented; syncoxa bearing 2 endites, with 3 setae on first endite and 2 on second; basis with strong claw plus 1 seta; small endopod with 1 seta on first segment and 3 setaeon second. Maxilliped ( Fig. 362C ) as small lobe bearing 4 setae.

Legs 1–4 ( Fig. 362 D-G) biramous with 3-segmented exopods; endopods 3-segmented inlegs 1–3, but 2- segmented in leg 4. Protopod 2-segmented in leg 1, but unsegmented in legs 2–4. Inner coxal seta absent in legs 1–4. Leg 1 lacking innerdistal element on basis. Outer seta on basis present only in leg 3. Endopod of leg 1 strongly curved inwards. First exopodal segment of legs 3 and 4 and second exopodal segment of legs 2 and 4 each bearing spiniform outer distal process. Outer setae on third exopodal segment of legs 2–4 vestigial. Armature formula for legs 1–4 as follows:

Leg 5 ( Fig. 361C ) consisting of outer lobe tipped with 1 small seta and inner, tapering, sclerotized process; left and right inner processes interconnected.

Male. Unknown.

Remarks.Itisnoteworthythat Ammonixysquadridens gen. et sp. nov. was extracted along with Doroixys obesa sp. nov. and two other species of copepods ( Scolecodes sp. and Haplostoma sp.), all from the same ascidian host.

Figures

FIGURE 361. Ammonixys quadridens gen. et sp. nov., female. A, habitus, dorsal; B, habitus, ventrolateral; C, leg 5 and urosome, ventral; D, anterior part of prosome, ventral; E, rostrum; F, antennule; G, antenna; H, labrum; I, mandible. Scale bars: A, B, 0.2 mm; C, D, 0.05 mm; E–I, 0.02 mm.

FIGURE 362. Ammonixys quadridens gen. et sp. nov., female. A, maxillule; B, maxilla; C, maxilliped; D, leg 1; E, leg 2; F, leg 3; G, leg 4. Scale bars: A–C, 0.01 mm; D–G, 0.02 mm.