Thoracodelphys tertius, 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 : 424-427

Thoracodelphys tertius sp. nov.

( Figs. 280 , 281 )

Typematerial. Holotype (intact ♀, MNHN-IU-2014- 21346 ) , paratypes (2 intact ♀♀, MNHN-IU-2014-21347), anddissectedparatype (1 ♀, figured) from Symplegma brakenhielmi (Michaelsen, 1904) (MNHN-IT-2008- 8440 = MNHN S1/ SYM /12), Côte sud de Grande Terre, Saint François, Guadeloupe, Stn 18. Monniot coll., 25 December 1980.

Etymology. The specific name is derived from the Latin terti (=third), as the new species is the third to be discovered in the genus.

Description of female. Body ( Fig. 280A ) dorsoventrally depressed, comprising inflated prosome and small free urosome: body length 1.65 mm. Prosome stout, unsegmented, 1.27 mm long, gradually broadening towards posterior end and tapering anteriorly, in dorsal view. Cephalosome small, fused with metasome, with plane of fusion discernible only by lateral incision: entire metasome forming brood pouch, incorporating fused fifth pedigeroussomite.Freeurosome( Fig.280B )5-segmented, graduallynarrowingposteriorly: genitalsomite 63×178 μm; 4 abdominalsomites 73×135, 64×120, 49×109, and 63×100 μm, respectively. Caudal rami slender, widely separated from each other; each ramus ( Fig. 280C ) about 5.1 times longerthan wide (132×26 μm): armed with 6 setae, outer proximal and dorsal setae located at 38 and 76% of ramus length, respectively; 4 distalsetae short, subequal in length, 3 spiniform and bluntly tipped.

Rostrum short, widerthan long, withrounded apex. Antennule ( Fig. 280D ) small, stout, 112 μmlong, 7- segmented, and stronglytapering from second to distal segments; compound second segment subdivided by 2 incomplete anterior suture lines; armatureformula 3, 14+spine, 8, 4+aesthetasc, 1, 4+aesthetasc, and 7+aesthetasc; spine on second segment spinulose; all setae naked, many large; 2 larger setaeonfirst segment especially large, longerthan entire antennule. Antenna ( Fig. 280E ) 4-segmented; coxa unarmed; basis 50×32 μm, bearing 1 small setae near outer distal corner; first endopodal segment 47×32 μm, unarmed; compound distal endopodal segment 59×22 μm, about 2.7 times longerthan wide: armedwith 7 setae (arranged as 2, 2, and 3 with distal seta as long as terminal claw) plus large terminal claw, about 45 μm long, 0.76 times as long as segment.

Labrum ( Fig. 280F ) strongly tapering, with narrow, setulose posterior margin and naked posteromedian lobe. Mandible ( Fig. 280G ) with 5 teeth and 1 small seta on coxal gnathobase; distalmost tooth acutely pointed, with minutespinulesalongproximal margin: basiswith 1 setaat mediodistal corner; exopod with 5 setae, distalmost about half length of other 4 setae; endopod obscurely articulated from basis, armed with 2 and 5 setae on first and second segments, respectively. Maxillule ( Fig. 280H ) bearing 8 setaeon arthrite, 1 on coxal endite; 2 on epipodite, 3 on basis, 3 on exopod, and 2 on endopod; proximal setaon basis small, less than half length of distal setae. Maxilla ( Fig. 281A ) 5-segmented; syncoxa with 9 setae arranged as 3, 1, 2, and 3 on first to fourth endites, respectively; basis with 3 setae, distal seta less than half length of middle seta; endopod 3-segmented with 1, 1, and 3 setae on first to third segments, respectively. Maxilliped ( Fig. 280I ) unsegmented with oblique distal margin, armed with 7 setae on medial margin and 1 seta at outer corner.

Legs 1–4 ( Fig. 281 B-E) biramous with 3-segmented exopods and 2-segmented endopods. Inner seta absent on coxa of legs 1–4. Inner distal spine on leg 1 basis 34 μm long, spinulose along margins. First exopodal segment of legs 1–4 bearing outer spine. Second exopodal segment bearing large, spiniform outer distal process, that of leg 4 bifurcate, but that of leg 3 simple or bifurcate. First and second exopodal segments of leg 4 lacking inner seta. First endopodal segment unarmed in legs 1 and 4. Armature formula for legs 1–4 as follows:

	Coxa	Basis	Exopod	Endopod
Leg 1	0-0	1-I	I-1; 1-1; 3, 1, 4	0-0; 1, 2, 3
Leg 2	0-0	1-0	I-1; 1-1; 3, 1, 5	0-1; 1, 3, 4
Leg 3	0-0	1-0	I-1; 1-1; 2, 1, 5	0-1; 1, 3, 4
Leg 4	0-0	1-0	I-0; 1-0; 2, 1, 5	0-0; 1, 3, 0

Leg 5 ( Fig. 281F ) represented by 2 small lobes; outer (protopodal) lobe rounded with 1 seta; inner (exopodal) lobe strongly tapering, shorter than wide, not articulated at base, armed with 1 vestigial inner seta and 1 larger outer apical seta.

Male. Unknown.

Remarks. The two previously known species of Thoracodelphys together with the six new species described herein all exhibit the same setation on the mandibular endopod and on the endopods of legs 1–4. In contrast, the setation of the mandibular exopod and of the first and second exopodal segments of legs 2–4 varies with species. The first exopodal segments of legs 2–4 of T. tertius sp. nov. each bear an outer spine, unlike the two already described species, T. chelipus and T. uniseta , each of which carries an outersetaon this segment. Theabsence of an anterodistal process on the first exopodal segment of legs 2–4, the 7-segmented antennule (6-segmented in T. chelipus and T. uniseta ), and the possession of 7 medial setae (6 in these two species) on the maxilliped are also distinguishing features of this new species.

Figures

FIGURE 280. Thoracodelphys tertius sp. nov., female. A, habitus, right; B, urosome, ventral; C, right caudal ramus, ventral; D, antennule; E, antenna; F, labrum; G, mandible; H, maxillule; I, maxilliped. Scale bars: A, 0.2 mm; B, 0.1 mm; C–E, G–I, 0.02 mm; F, 0.05 mm.

FIGURE 281. Thoracodelphys tertius sp. nov., female. A, maxilla; B, leg 1; C, leg 2; D, leg 3; E, leg 4; F, leg 5. Scale bars: A, F, 0.02 mm; B–E, 0.05 mm.