Lernanthropus kazachenkoi Kovaleva, 2025

Lernanthropus kazachenkoi Kovaleva , sp. nov.

( Figs 4–7 View FIGURE 4 View FIGURE 5 View FIGURE 6 View FIGURE 7 )

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 easily differs from those of other species by the following characters: fourth and fifth antennules ornamented with dense surface covering of long setules ( Figs 6D View FIGURE 6 , 7A View FIGURE 7 ); second antenna 4-segmented ( Fig. 6F,H View FIGURE 6 ); egg sacs loosely proximal straight and then begin to curl between the fourth pair of legs ( Fig. 6B,C View FIGURE 6 ). Male is unknown.

Description of female holotype. Body relatively strong and thick, strongly convex both dorsally and ventrally ( Figs 4A–C View FIGURE 4 , 6A–C View FIGURE 6 ). Length 3.65 mm (from anterior rim of head to end of dorsal trunk plate). Cephalon is fused with first trunk segment to form a cephalothorax. Body comprising cephalothorax and trunk. Cephalothorax sub quadrangular; longer than wide with almost linear lateral margins narrowing anteriorly towards short frontal margin ( Figs 4A View FIGURE 4 , 6A View FIGURE 6 ); with distinct dorsal cephalothoracic shield. Cephalothorax 1х 0.95 mm. From the top of cephalothorax, on anterior margin, there are two conical projections and a small hard shield; from base, hard shield descends, forming margins and a second hard shield. Lateral margins of cephalothorax are directed ventrally. Antennule is located between conical projections and hard shield ( Figs 6A View FIGURE 6 , 7A View FIGURE 7 ). Trunk distinctly wider than cephalothorax: second and third trunk segments form anterior part of trunk and 1 well-defined dorsal tergites derived from second and third pedigerous somites. Protopodites of 3rd legs are formed on sides of front part of trunk (second and third pedigerous somites); very similar to plates, placed obliquely and projecting slightly forwards and considerably backwards ( Figs 4A,C View FIGURE 4 , 6A,C View FIGURE 6 ). Protopodites of 3rd legs 1.60х 1.05 mm. Dorsal trunk plate covering fourth pedigerous somite and entire urosome. Urosome comprising fifth pedigerous somite, genital complex and abdomen, all fused; bearing paired, elongate caudal rami on ventral surface. Trunk without dorsal trunk plate 0.75x 1.80 mm. Entire dorsal surface of trunk ornamented with cuticular tubercles. Dorsal trunk plate 1.90х 1.25 mm, abruptly constricted at two-thirds of its distance from base, and further on narrows to end in a distinctly bilobed broad apex. Paired caudal rami elongate, tapering tip; 3-segmented ( Fig. 7J View FIGURE 7 ). Genital complex and abdomen with caudal rami covered by 3rd legs whose branches are fused in middle. Abdomen 1-segmented, rounded. Caudal rami each with six bare setae. Egg sacs are loosely proximal straight and then begin to curl between fourth pair of legs, wrapping around them ( Fig. 6B,C View FIGURE 6 ). Antennule ( Figs 6D, E View FIGURE 6 , 7A View FIGURE 7 ) distinctly 7–segmented, 4 and 5 segments covered with dense long setules, some segments with irregular cuticular thickening; setal formula: 0, 1, 4, 3, 0, 12. Parabasal flagellum curved, with broad base tapering towards slender tip ( Fig. 6K View FIGURE 6 ). Parabasal flagellum is located between antennules and antennae, near conical processes. Antenna ( Figs 5 View FIGURE 5 , 6F–J View FIGURE 6 ) 4-segmented; body robust; proximal segment with papillary element; second segment armed with four spines, distal part with circular ridges of different size; other segments unarmed. Postantennal process ( Fig. 7B View FIGURE 7 ) located just posterior to antenna, towards lateral margin of anteroventral cephalic region; two discs are crescent shaped and connected to each other. Mandible slender, stylet-like, armed with eight marginal teeth distally ( Fig. 6L View FIGURE 6 ). Maxillule ( Fig. 7C View FIGURE 7 ) bilobate, comprising small inner lobe tipped with one spiniform element and larger outer lobe; lobe armed with three unequal spiniform elements. Maxilla ( Fig. 7D View FIGURE 7 ) 2-segmented; comprising proximal syncoxa (lacertus) and distal basis (brachium); basis ornamented with claw-like process distally, ornamented with patch of spinules distally; terminal claw armed with sharp denticles on inner surface. Maxilliped ( Fig. 7E View FIGURE 7 ) 3-segmented, proximal segment unarmed with stout calf. Third segment without spines; shortest and strongly curved. Leg 1 robust, members of leg pair joined by intercoxal sclerite ( Fig. 7F View FIGURE 7 ). Each leg biramous with stout inner spine on basis; basis ornamented with patches of spinules: exopod 1-segmented, armed with 5 robust terminal spines and ornamented with spinules distally; endopod 1-segmented, armed with very long terminal seta about 2 times longer than segment, and ornamented with spinules. Leg 2 forming large ventrally directed lobe ( Fig. 7G View FIGURE 7 ) derived from protopod armed with outer seta, and carrying small, 1-segmented rami distally; lacking intercoxal sclerite; exopod armed with four vestigial spines; endopod lobate, unarmed. Leg 3 ( Figs 4B View FIGURE 4 , 6B View FIGURE 6 ) very large, biramous, modified by complete fusion of rami into large U-shaped lamellae, with branches almost equally fused in the middle. Composed of a large, fleshy lateral lamella (exopod) and a small, blunt process (endopod) fused along medial margin with another member of same pair. Protopod of 3rd leg projecting as large lobes on either side of trunk. Leg 4 ( Fig. 7H View FIGURE 7 ) foliaceous and biramous; protopod short and narrow; both rami highly flattened and divisible into lamellate, broad basal part and filiform, narrow distal part; outer (exopodal) lobe slightly longer than inner (endopodal). Leg 5 reduced to short conical process, unarmed ( Fig. 7I View FIGURE 7 ). Male. Unknown.

Etymology. The new species is named in honor of the scientist, my teacher, Prof. Vasili N. Kazachenko (1940– 2024), who studied parasitic copepods of fishes.

Remarks. Lernanthropus kazachenkoi sp. nov. most closely resembles L. caudatus , L. longilamina , L. hexodonis sp. nov., L. manicatus , L. marginatus sp. nov., L. nemipteri , L. pagelli , and L. scribae . Distinguishing features between all new species described here are mentioned above in the differential diagnosis of L. hexodonis sp. nov.

The following characters differ the new species from L. caudatus : the distal part of the dorsal trunk plate narrows sharply at two thirds of the distance from the base, ending in a distinctly bilobed apex, and in L. caudatus it is uniformly and smoothly rounded; 4 and 5 segments of the antennule ornamented with a dense surface covering of long setules, whereas L. caudatus lacks such setules; the new species has a parabasal flagellum, whereas L. caudatus lacks one; the antenna is 4-segmented, the second segment armed with four spines, in L. caudatus 2-segmented and the second segment with a single spike at the base on the inner edge of the claw.

The new species differs from L. longilamina in the shape of the cephalothorax. Antennule of the new species is 7-segmented, whereas L. longilamina is 6-segmented. The new species differs from L. longilamina in the antenna structure: L. longilamina is 2-segmented and L. kazachenkoi sp. nov. is 4-segmented.

L. kazachenkoi sp. nov. resembles L. manicatus in general appearance and size, but a number of features prevent it from being placed in the same species: in the new species, the dorsal trunk plate ends with a clearly bilobed apex, whereas in L. manicatus the posterior margin of the dorsal plate is flat, without notches; L. manicatus antennule 2-segmented, second segment with one spike at base on inner margin of claw, and L. kazachenkoi sp. nov. 4-segmented, the second segment armed with four spines; the exopodite of the 1st leg of L. manicatus has six spines at the distal end, whereas L. kazachenkoi sp. nov. has five spines; 4th legs in L. kazachenkoi sp. nov. barely reach the constriction of the dorsal trunk plate, in L. manicatus they protrude behind the dorsal trunk plate for a third of their length.

L. kazachenkoi sp. nov. differs from L. marginatus sp. nov. in the form of Antennule structure: L. kazachenkoi sp. nov. is 7-segmented, 4 and 5 segments ornamented with a large numerous long, thin setules, and L. marginatus sp. nov. is 8-segmented and segment 4 and 5 is unornamented with a large numerous long, thin setules. In L. kazachenkoi sp. nov. antennule 4-segmented, and L. marginatus sp. nov. 2-segmented. In L. kazachenkoi sp. nov. postantennal process in shape of two discs that are crescent and connected each other whereas in L. marginatus sp. nov. in horseshoe shape. In L. kazachenkoi sp. nov. second segment maxillae is armed with a spike, and in L. marginatus sp. nov. is armed bifurcated spike. Endopodite 1st leg of L. kazachenkoi sp. nov. is armed with a long spike, whereas L. marginatus sp. nov. is unarmed. Exopodite 2nd leg of L. kazachenkoi sp. nov. is armed with four small spines, and in L. marginatus sp. nov. is armed with five. Egg sacs of L. kazachenkoi sp. nov. are twisted between the fourth pair of legs, which in L. marginatus sp. nov. egg sacs linear and thick, longer than dorsal trunk plate.

The new species resembles L. nemipteri in general appearance, but differs in details of limb structure: first and second trunks are dorsally fused, and in L. nemipteri they are separated; antennule in L. kazachenkoi sp. nov. 7- segmented, as L. nemipteri has an 8-segmented antennule; L. kazachenkoi sp. nov., fourth and fifth antennal segments ornamented with a dense surface covering of long setules, which L. nemipteri lacks. absent in L. nemipteri ; antenna of the new species is 4-segmented and the second segment is armed with four spines, whereas in L. nemipteri it is 2-segmented and the second segment has one spine; third segment of maxilliped in L. kazachenkoi sp. nov. without appendicular process, and in L. nemipteri with conspicuous blunt appendicular process; egg sacs of L. kazachenkoi sp. nov. are twisted between the fourth pair of legs, which in L. nemipteri are comparatively short but stout, direct, not reaching the distal border of the dorsal trunk plate.

As far as the general appearance is concerned, L. kazachenkoi sp. nov. resembles L. pagelli . However, L. kazachenkoi sp. nov. differs from L. pagelli by the folloing: 1) L. pagelli has a small notch on the sides of the cephalothorax, L. kazachenko i sp. nov. does not; 2) dorsal trunk plate of L. kazachenkoi sp. nov. forms a notch at the posterior margin, whereas in L. pagelli the notch is practically invisible; 3) in L. pagelli , the exopodite of the fourth leg bears a small spike at the distal end, and in L. kazachenkoi sp. nov. without a spike.

New species is closer to L. scribae . Nevertheless, L. kazachenkoi sp. nov. can be easily separated from L. scribae by the following: 1) in L. kazachenkoi sp. nov. the lateral margins of the cephalothorax are flat, and in L. scribae there is a small notch on the sides of the cephalothorax; 2) dorsal trunk plate of L. kazachenkoi sp. nov. ends in a distinct bilobed apex, and in L. scribae the posterior edges of the dorsal trunk plate lack a bilobed apex.