Thermocheres viridis, Lee, 2025

Lee, Il-Hoi Kim and Taekjun, 2025, Ten new species of siphonostomatoid copepods (Crustacea) associated with marine invertebrates from Korea, Journal of Species Research 14 (2), pp. 146-181 : 167-170

Thermocheres viridis n. sp. ( Figs. 14 , 15 )

https://zoobank.org/urn:lsid:zoobank.org:act:B84E8AF3-

1CC9-462A-B7C1-CD3A88BF661B

Type material. Holotype (♂, dissected and mounted on a slide; MABIK CR00257789 ) was collected from mixed species of sponges near Munseom , Seogwipo , Jeju Island (33°13 ʹ 39.4 ʺ N, 126°33 ʹ 48.2 ʺ E), SCUBA, at a depth of 56 m, by Taekjun Lee , on 25 April 2023. The holotype has been deposited in the National Marine Biodiversity Institute of Korea ( MABIK), Seocheon.

Etymology. The name deriveds from Latin virid (= greenish) and refers to the greenish body color of the new species.

Male. Body ( Fig. 14A ) greenish, 1.03 mm long. Prosome 629 μm long. Cephalothorax 418 × 473 μm. All prosomal somite with acutely pointed posterolateral corners. Urosome ( Fig. 14B ) 6-segmented. Fifth pedigerous somite 130 μm wide. Genital somite nearly quadrangular, wider than long (109 × 165 μm), bearing acutely pointed posterolateral corners; genital operculum with cusp on subdistal inner margin. Four abdominal somites 55 × 125, 47 × 109, 31 × 93, and 45 × 95 μm, respectively; first and second abdominal somites with acutely pointed, posteriorly extended posterolateral corners. Anal somite with minute spinules on posteroventral margin. Caudal rami slightly divergent; each ramus ( Fig. 14C ) 2.02 times longer than wide (85 × 42 mm), slightly narrowing distally, armed with 6 setae and ornamented with thin setules on inner margin and membranous fringe on posteroventral margin; setae II and VII positioned subdistally and dorsally at same plane.

Rostrum ( Fig. 14D ) lightly longer than wide, tapering, with rounded distal apex. Antennule ( Fig. 14E ) 17-segmented, geniculated between fifteenth and sixteenth segments; First to fifth, seventh, eleventh, and fourteenth segments each with 2 setae + aesthetasc, sixth and tenth segments each with 2 setae, nineth segment with 7 setae + 3 aesthetascs, twelfth segment each with 4 setae + aesthetasc, thirteenth and fifteenth segments each with 1 seta; penultimate segment with 1 seta + aesthetasc, and terminal segment with 11 setae; all setae naked. Aesthetasc on penultimate segment about 0.6 times as long as entire segments; aesthetascs on other segments thin, generally as long as that of penultimate segment. Antenna ( Fig. 14F ) slender, consisting of coxa, basis, 1-segmented exopod, and 2-segmented endopod; coxa 27 μm long, unarmed; basis 64 μm long, unarmed but ornamented with longitudinal row of pectinated spinules along distal half; exopodal segment 17 × 5.5 μm, bearing 3 setae; first endopodal segment 35 μm long, unarmed but with thin spinules on inner and outer margins; second endopodal segment 29 μm long, terminated in elongated spine (120 μm long), with 3 pinnated setae (1 proximal and 2 distal) and setules on outer surface.

Oral siphon ( Fig. 14J ) 380 μm long, slender, evenly narrowing distally. Mandible ( Fig. 14G ) consisting of segment-like coxa, thin stylet, and small palp; stylet 354 μm long, bearing 11 teeth at distal region ( Fig. 14I ); palp ( Fig. 14H ) small, digitiform, unsegmented, not articulated from coxa, tipped with 2 small setae. Maxillule ( Fig. 14G ) bilobed; outer lobe small, 25 μm long, bearing 4 setae (2 distal and 2 subdistal); inner lobe 104 μm long, distally armed with 1 rudimentary and 3 extremely long setae, latter 3 setae subequal in length, blunt and spinulose at tip. Maxilla ( Fig. 15A ) slender, 2-segmented; both segments unarmed; distal segment terminated in spiniform claw, with 1 minute seta at distal third and several setules distally; claw spinulose, about 0.38 times as long as segment. Maxilliped ( Fig. 15B ) consisting of syncoxa, basis, and 3-segmented endopod; armature formula 1, 1, 2, 2, and 1 + claw; basis with rounded protrusion, its inner seta minute, positioned at distal region of protrusion; setae on second and third endopodal segments pinnate; third endopodal segment 54 μm long; terminal claw 95 μm long, bearing spinules along concave margin.

Legs 1-4 ( Fig. 15C- F ) with 2-segmented protopod and 3-segmented rami; all these legs with pinnate inner seta on coxa and pinnate outer seta on basis. Leg 1 basis with thin, naked inner distal seta and spinules on inner distal corner. Second endopodal segment of legs 1-4 with bicuspid outer distal corner. Leg 4 with rudimentary inner distal seta on third exopodal segment. Armature formula for legs 1-4 as follows:

Coxa Basis Exopod Endopod

Leg 1 0-1 1-1 I-1; I-1; III, 2, 3 0-1; 0-2; 1, 2, 3 Leg 2 0-1 1-0 I-1; I-1; III, I, 5 0-1; 0-2; 1, 2, 3 Leg 3 0-1 1-0 I-1; I-1; III, I, 5 0-1; 0-2; 1, 1 + I, 3 Leg 4 0-1 1-0 I-1; I-1; III, I, 5 0-1; 0-2; 1, 1 + I, 2

Leg 5 ( Fig. 15G ) consisting of pinnate dorsolateral seta of fifth pedigerous somite and small, free exopod; exopodal segment 1.24 times longer than wide (21 × 17 μm), bearing 3 setae of unequal lengths, longest one pinnate, others naked. Leg 6 ( Fig. 14B ) represented by 2 small distal setae and 1 subdistal cusp on genital operculum.

Female. Unknown.

Remarks. The genus Thermocheres includes two species, T. validus Kim, 2010 , known from Madagascar, and T. pacificus Lee, Chang and Kim, 2022 from Korea ( Kim, 2010; Lee et al., 2022). Although differences between species of Thermocheres are slight, T. viridis n. sp. is distinguishable from the two congeners: (1) by the one-segmented mandibular palp tipped with two setae, as opposed to the palp represented by a vestigial seta in T. validus or the absence of a palp in T. pacificus ; (2) by possessing the rudimentary inner distal seta on the third endopodal segment of leg 4, as opposed to the seta well-developed seta in T. validus or the reduced size in T. pacificus ; and (3) by having a rounded distal apex of the rostrum, in contrast to the acutely pointed, beak-like apex in T. validus or the angular apex in T. pacificus . Additionally, the new species features one spine plus four setae (formula 1, 1 + I, 2) on the third endopodal segment of leg 4, further distinguishing it from T. pacificus (formula 1, I, 2 in the latter species).

Figures

Fig. 14. Thermocheres viridis n. sp., male.A, habitus, dorsal; B, urosome, ventral; C, left caudal ramus, dorsal; D, rostrum; E, antennule; F, antenna; G, mandible and maxillule; H, proximal part of mandible; I, distal part of mandible; J, oral siphon. Scale bars:A, J, 0.1 mm; B, E, G, 0.05mm; C, D, F, H, 0.02 mm; I, 0.01mm.

Fig. 15. Thermocheres viridis n. sp., male.A, maxilla; B, maxilliped; C, leg 1; D, leg 2; E, leg 3; F, leg 4; G, leg 5. Scale bars: A-F, 0.05 mm; G, 0.02mm.