Lernanthropus marginatus Kovaleva, 2025

Lernanthropus marginatus Kovaleva , sp. nov.

( Figs 8–11 View FIGURE 8 View FIGURE 9 View FIGURE 10 View FIGURE 11 )

Lernanthropus nemipteri View in CoL : Kazachenko et al. 2018: 35; 2020:18; Hà et al. 2020: 212-214. Misidentification.

Type material. Holotype ♀ from Nemipterus marginatus ( Nemipteridae ), Vietnam, Hai Phong ( Gulf of Tonkin ), 12.IV.2016, female in 1 of 3 examined fishes, gill lobes, collected by V.N. Kazachenko, [ EATB].

Diagnosis. Female of the new species can be distinguished from those of other species by the combination of the following characters: the antennule 8-segmented ( Fig. 10E,F View FIGURE 10 ); the postantennal process horseshoe shape ( Fig. 10J View FIGURE 10 ); the maxillule with the endopodite at apex with 1 spike ( Fig. 11B View FIGURE 11 ), and the exopodite covered with small spines; the endopodite of the leg 1 is unarmed ( Fig. 11E,F View FIGURE 11 ); the exopodite of the leg 2 is armed with five spikes ( Fig. 11G View FIGURE 11 ); the leg 5 with spike ( Fig. 11J View FIGURE 11 ); the egg sacs linear and thick, longer than dorsal trunk plate ( Fig. 10A–D View FIGURE 10 ).

Description of female holotype. Body is stocky and rather thick ( Figs 8A–C View FIGURE 8 , 9 View FIGURE 9 , 10A–D View FIGURE 10 ), comprising cephalothorax, trunk and small urosome concealed beneath dorsal trunk plate. Trunk wider than cephalothorax, first thoracic segment is part of cephalothorax. Cephalothorax about as long as wide; lateral margins slightly convex in dorsal view and produced ventrally and anteriorly into conspicuous “horns” either side of frontal margin; with large, ventrally produced lateral flaps. From top of cephalothorax, on anterior margin, there is small hard shield. From base, hard shield descends, forming margins and a second hard shield. Antennules are located between anterolateral parts of cephalothorax and chitinous shield ( Fig. 10A,F View FIGURE 10 ). Trunk carries dorsally single small, convex and single large, semicircular dorsal trunk plate. Second to third trunk somites completely fused, laterally forming protopodites of 3rd legs. Fourth thoracic segments form a swollen trunk with a dorsal trunk plate. Dorsal trunk plate covering fourth pedigerous somite and entire urosome, at two-thirds of distance from base tapers sharply, ending in a distinctly bilobed broad apex. Entire dorsal surface dorsal trunk plate and protopodites of 3rd legs rigid and strongly sclerotized, ornamented externally with tubercles. Urosome consisting of fifth pedigerous somite, genital complex and abdomen, all fused together.Abdomen 1-segmented, rounded. Caudal rami paired, with bluntly rounded apex, 3-segmented and ornamented with short setules ( Fig. 11K View FIGURE 11 ). First segment on proximal part is armed with two long, plumose setae and a bare bristle on distal end. Second segment at distal end is armed with single bristle located in middle. Two bristles are located apically at distal end of third segment. Egg sacs linear and thick, longer than dorsal trunk plate. Body total length 4 mm (from anterior rim of head to end of dorsal trunk plate). Cephalothorax 1.00х 0.95 mm. Trunk without dorsal trunk plate 1.00х 0.95 mm and width with protopodites of 3rd legs 2.10 mm. Dorsal trunk plate 2.05х 1.30 mm. Protopodites of 3rd legs 1.55–1.75 (1.65)х0.90–0.95 (0.93) mm. Genital complex 0.175х 0.25 mm. Abdomen 0.1х 0.25 mm. Caudal rami 0.13х 0.03 mm. Egg sacs 1.75–2.40 (2.07)х0.35–0.9 (0.63) mm. Antennule ( Fig. 10E,F View FIGURE 10 ) 8-segmented with irregular cuticular thickening; setal formula: 0, 1, 4, 3, 4, 1, 0, 6. Parabasal flagellum with swollen base and long distal part, curved at tip ( Fig. 10G,H View FIGURE 10 ); located near conical projections, between the antennule and the antenna ( Fig. 10I View FIGURE 10 ). Antenna ( Fig. 10K View FIGURE 10 ) 2-segmented, robust; first segment armed with papilliform element proximally on medial surface; second segment terminating in strongly recurved claw bearing spinous process proximally on concave margin. Postantennal process ( Fig. 10J View FIGURE 10 ) is horseshoe shape without ornamentation, located just behind base of antennae. Mandible stylet-like, armed with eight marginal teeth distally ( Fig. 11A View FIGURE 11 ). Maxillule ( Fig. 11B View FIGURE 11 ) bilobate, smaller lobe tipped with one spiniform element; larger lobe tipped with three unequal spiniform elements distally and ornamented with surface spinules. Maxilla ( Fig. 11C View FIGURE 11 ) 2-segmented,comprising massive lacertus (syncoxa) and long brachium (basis) terminating in apical claw-like element; brachium ornamented with patch of spinules and single bifid process distally; terminal claw armed with two rows of sharp denticles on inner surface. Maxilliped ( Fig. 11D View FIGURE 11 ) 3-segmented, core segment comprising massive corpus, with papilliform element on medial surface, and distal subchela; second segment without spikes; third segment unarmed. Leg 1 with well defined protopod and members of leg pair joined by intercoxal sclerite: biramous ( Fig. 11E,F View FIGURE 11 ) with strong inner spine on basis: rami 1-segmented: basipod and both rami carry prominent scattered sharp teeth. Exopod 1-segmented, armed with 5 robust terminal spines with denticulate margins; endopod 1-segmented, smoothly tapering to unarmed apex. Leg 2 ( Fig. 11G View FIGURE 11 ) biramous with 1-segmented rami; mounted on inflated subspheri cal prominence derived from incorporated protopod and armed with outer seta; exopod represented by rod-like process bearing five blunt, conical spines; endopod lobate, unarmed; lacking intercoxal sclerite; both rami ornamented with spinules. Leg 3 biramous, large and modified into large U-shaped laminae by complete fusion of rami ( Fig. 11H View FIGURE 11 ). Protopods enlarged into large elytra-like lobes, partially fused with trunk and extending anteriorly to posterior margin of cephalothorax; rigid and strongly sclerotized, ornamented externally with tubercles. Exopod fleshy lateral lamella and small (endopod) blunt process fused along medial margin with another member of same pair. Leg 4 ( Fig. 11I View FIGURE 11 ) is modified into a pair of long bilobate processes; biramous; rami are fattened narrowing distalwards; lobes of similar length. Leg 5 ( Fig. 11J View FIGURE 11 ) is a small blunt process with a short apical seta. Male. Unknown.

Etymology. The name of the new species refers to the species name of its only known host.

Remarks. The complex of diagnostic characters (antennule, maxilla, 1st leg, 2nd leg, 4th leg, 5th leg) and external structure allows the newly described species to be easily distinguished from Lernanthropus caudatus , L. hexodonis sp. nov., L. longilamina , L. kazachenkoi sp. nov., L. manicatus , L. nemipteri , L. pagelli , and L. scribae .

L. marginatus sp. nov. is closely related to L. caudatus , from which it differs in the shape of the dorsal trunk plate: in L. caudatus , the distal part of the dorsal trunk plate is uniformly and smoothly rounded, and the new species at two-thirds of the distance from the base tapers sharply, ending in a distinctly bilobed broad apex. Antennule of the L. caudatus is 7-segmented, whereas new species is 8-segmented. L. caudatus lacks a parabasal flagellum, whereas L. marginatus sp. nov. possesses one. The endopodite of the first leg in L. caudatus has a glabrous apical spike, unlike L. marginatus sp. nov., which is unarmed.

L. marginatus sp. nov. differs from L. kazachenkoi sp. nov. by the characters given above.

In L. marginatus sp. nov. the antennule is 8-segmented, and in L. longilamina it is 6-segmented. In the new species, the second antennal segment bears a small spike in the middle, whereas L. longilamina has two small spines. The endopodite of the first leg in L. longilamina is armed with a long, glabrous apical spike, whereas L. marginatus sp. nov. has no spike. L. marginatus sp. nov. bears five chitinous spines on the distal end of the exopodite of the second leg, the endopodite is unarmed, and in L. longilamina the exopodite is covered with small bristles with one spine and one long spine on the endopodite. The exopodite of the 4th leg of L. longilamina has a short sharp spike at the distal end, whereas L. marginatus sp. nov. has no spike. In L. marginatus sp. nov. the dorsal trunk plate terminates in a clearly bilobed apex, whereas in L. longilamina the posterior margin of the dorsal trunk plate is rounded.

L. marginatus sp. nov. resembles L. manicatus . The new species differs from L. manicatus in that the following: 1) the dorsal plate of L. marginatus sp. nov. has a notch on the posterior margin, which is absent in L. manicatus ; 2) in the new species the exopodite of the 1st leg bears five spines at the distal end, in L. manicatus six spines; 3) in L. marginatus sp. nov. the endopodite of the 1st leg is without a spike, whereas in L. manicatus the endopodite is armed with a terminal spike; 4) exopodite of the 2nd leg in L. marginatus sp. nov. is armed with five spines at the distal end and the endopodite is not armed, as in L. manicatus the exopodite is armed with four small spines and the endopodite is bare; 5) in the new species 4th legs barely reach the constriction of the dorsal trunk plate, in L. manicatus they protrude a third of their length beyond the dorsal trunk plate.

The new species is very similar to L. nemipteri in general appearance and size, found also on a related host, but a number of features still prevent it from being attributed to the same species. In L. nemipteri , the second and third trunk compartments are divided dorsally into two distinct segments, and in L. marginatus sp. nov. they are undivided; L. nemipteri has the 3rd segment of the maxilliped distally strongly curved and carries a prominent blunt accessory process, whereas L. marginatus sp. nov. does not; the endopodite of the 1st leg in L. nemipteri is armed with a short naked apical spike, whereas L. marginatus sp. nov. has no spike; 5th leg in L. nemipteri without spike, and in L. marginatus sp. nov. with terminal spike; egg sacs in L. nemipteri comparatively short but stout, just reaching the tip of the outer ramus of 4th legs, stopping far short of the tip of the dorsal trunk plate, while in L. marginatus sp. nov. longer than the dorsal trunk plate.

L. marginatus sp. nov. resembles L. pagelli in body structure, but it differs in the following: 1) dorsal trunk plate of new species forms a notch at posterior margin, whereas in L. pagelli , this notch is almost invisible; 2) in new species 4 leg reaches the constriction of the dorsal trunk plate, and in L. pagelli they reach the end of the dorsal trunk plate; 3) 5 leg with a terminal spike in new species, whereas unarmed in L. pagell .

L. marginatus sp. nov. resembles L. scribae in general appearance and size, but a number of features prevent it from being placed in the same species: 1) in L. scribae posterior edges of the dorsal trunk plate without bilobed apex, and in new species distal margin with conspicuous, deep medial sinus; 2) antennule in L. scribae 7-segmented, as L. marginatus sp. nov. has an 8-segmented antennule; 3) in L. scribae , the endopodite of the 1st leg is armed with a long, naked spike, whereas in L. marginatus sp. nov. no spike; 4) in L. scribae 4th legs reach the end of the dorsal trunk plate, whereas new species reaches the constriction of the dorsal trunk plate.