Thoracodelphys depressa, 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 : 432-435

Thoracodelphys depressa sp. nov.

( Figs. 286 , 287 )

Typematerial. Holotype (intact ♀, MNHN-IU-2014- 21350 ) , paratype (intact ♀, MNHN-IU-2014-21351), and dissected paratype (♀, figured) from Botryllus gregalis (Sluiter, 1898) , AURACEA 1995, Ibo, Mozambique, intertidal, sea grass beds, mangroves and barrier reef, C. Monniot coll., November 1995.

Etymology. Thespecific namerefers to the markedly dorsoventrally depressed prosome of the new species.

Descriptionoffemale. Body ( Fig. 286A ) strongly dorsoventrally depressed; bodylength 0.98 mm. Prosome 0.83 mm long, taperinganteriorly, truncate posteriorly: comprising cephalosome and 4 pedigerous somites, but articulation between third and fourth pedigerous somites indistinct dorsally. Greatest width of prosome 440 μm at level of fourth pedigerous somite. Freeurosome ( Fig. 286B ) 5-segmented: genital somite distinctly wider than abdomen, 39×124 μm; 4 abdominalsomites 55×97, 47×90, 38×86, and 59×79 μm, respectively. Anal somite with deep, broad posteromedian incision and 3 small spinules on posteroventral border at base of caudal rami ( Fig. 286C ). Caudal rami slender, widely separated from each other; each ramus ( Fig. 286C ) about 6.1 times longer than wide (110×18 μm) and about twice as long as anal somite, graduallynarrowing distally: armedwith 6 setae (1 proximal, 1 subdistal, and 4 distal); proximal and subdistal setae located at 30 and 68% of ramus length, respectively; 3 of 4 distalsetae spiniform, stiff, and bluntly tipped, remaining seta pale and attenuated.

Rostrum ( Fig. 286D ) short, muchwiderthanlong, withrounded apex. Antennule ( Fig. 87E ) small, 117 μm long, 7-segmented; first and second segments much broader than distal segments; armature formula 3, 14, 8, 4+aesthetasc, 1, 3+aesthetasc, and 9+aesthetasc; setae crowded, naked, and generally long; longest setaon first segment slightly longerthan entire antennule. Antenna ( Fig. 286F ) 4-segmented; coxashortand unarmed; basis 33×20 μm, with 1 smallseta distally; firstendopodal segment 35×22 μm, unarmed; compounddistalendopodal segment 42×13 μm, about 3.2 timeslongerthan wide: armed with 7 setae arranged as 3, 2, and 2 (1 proximal seta long, extending beyond distal tip of terminal claw; 2 distal setae bluntly tipped), plus terminal claw half as long as segment.

Labrum ( Fig. 286G ) withsmall posteromedian lobe and ornamented with setules on distal surface. Mandible ( Fig. 286H ) with 5 teeth and 1 small seta on coxal gnathobase, distalmost tooth acutely pointed: basis with 1 setaat mediodistal corner; exopod with 5 unequal setae; setae gradually becoming shorter from proximal to distal; shortest seta about one third length of largest; endopod with 2 and 5 setae on first and second segments, respectively; longest second outer seta on distal margin directed mediodistally. Maxillule ( Fig. 286I ) armed as in T. longiseta sp. nov.; small proximal seta on basis pale, about one-third as long as middle seta. Maxilla ( Fig. 287A ) segmented and armed as in T. longiseta sp. nov.; distal seta on basis less than half length of middle seta. Maxilliped ( Fig. 287B ) unsegmented, armedwith 8 medial setae and 1 outer subdistal seta; ornamented several rows of minute spinules on outer side.

Legs 1–4with 3-segmentedexopods and 2-segmented endopods ( Fig. 287 C-F). Innercoxalsetaabsentinlegs 1–4. Outer seta on basis small. Inner distal spine on basis of leg 1 elongate, 35 μm long, spinulose, extending to middle of second endopodal segment. Second exopodal segment of leg 1 with 3 spinules on anterodistal margin. Three outer setae on third exopodal segment of leg 1 bluntly tipped in left leg but attenuated in right leg. Outer setae on exopods of legs 2 and 3 small and bluntly tipped. First exopodal segment of legs 1–3 with large, tapering anterodistal process. Second exopodal segment of legs 2–4 with large, bifurcate anterodistal process. First and second exopodal segments and first endopodal segment of leg 4 unarmed. 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	1-1; 1-1; 3, 1, 5	0-1; 1, 2, 5
Leg 3	0-0	1-0	1-1; 1-1; 2, 1, 5	0-1; 1, 2, 5
Leg 4	0-0	1-0	0-0; 0-0; 2, 1, 5	0-0; 1, 3, 0

Leg 5 ( Fig. 287G ) consistingof short, broad protopod with 1 setaon outer margin, and small, strongly tapering free exopodal segment, 11×16 μm, armed distally with 2 setae; outer seta 15 μm, inner seta 16 μm.

Male. Unknown.

Remarks. The lack of a setal element (typically a seta in Thoracodelphys ) on the first and second exopodal segments of leg 4 is a unique feature of T. depressa sp. nov. within the genus. The strongly depressed prosome and the presence of three small spinules on the posteroventral margin of the anal somite, near the base of the caudal ramus, are also distinguishing features of the new species.

Figures

FIGURE 87. Pachypygus bisetiger sp. nov., female. A, paragnath; B, maxilla; C, leg 1; D, leg 2; E, leg 3; F, leg 4; G, leg 5. Scale bars: A, G, 0.02 mm; B–F, 0.05 mm.

FIGURE 286. Thoracodelphys depressa sp. nov., female. A, habitus, dorsal; B, urosome, ventral; C, right caudal ramus, ventral; D, rostrum; E, antennule; F, antenna; G, labrum; H, mandible; I, maxillule. Scale bars: A, 0.1 mm; B, 0.05 mm; C–I, 0.02 mm.

FIGURE 287. Thoracodelphys depressa sp. nov., female. A, maxilla; B, maxilliped; C, leg 1; D, leg 2; E, exopod of leg 3; F, leg 4; G, leg 5. Scale bars: 0.02 mm.