Nitocrella thailandensis, Boonyanusith & Brancelj & Sanoamuang, 2025

Boonyanusith, Chaichat, Brancelj, Anton & Sanoamuang, Laorsri, 2025, Two new species of Nitocrella (Copepoda, Harpacticoida) from a spring in Loei Province, northeastern Thailand, ZooKeys 1240, pp. 277-303 : 277-303

Nitocrella thailandensis sp. nov.

Figs 7 , 8 , 9 ( female); Figs 10 , 11 (male )

Type material.

Holotype: Thailand • 1 ♀ (adult), 595 μm long; northeast Thailand, Loei Province, Nong Hin District, Wat Tham Bodhisattva Temple , 17°05′13.19″N, 101°46′55.59″E, 337 m a. s. l.; 2 April 2023, A. Brancelj, L. Sanoamuang and N. Sanoamuang leg.; a concrete reservoir at mouth of karstic spring; access number: THNHM-IV-20716 ; completely dissected, mounted on a slide in glycerol, covered with coverslip and sealed with nail polish . Paratype 1 (“ allotype ”): Thailand • 1 ♂ (adult), 564 μm long; location, date, and collectors as for holotype; access number: THNHM-IV-20717 ; completely dissected, mounted on slide in glycerol, covered with coverslip and sealed with nail polish . Paratype 2: Thailand • 1 ♀ (adult); location, date, and collectors as for holotype; access number: THNHM-IV-20718 ; preserved in 70 % ethanol .

Additional material.

Thailand • 1 ♂ (adult), 1 ♀ (adult); location, date, and collectors as for holotype; preserved in 70 % ethanol; retained in a collection of the first author (CB) .

Description of adult female.

Total body length (measured from tip of rostrum to posterior margin of caudal rami) ranging from 539 µm to 595 µm (mean = 577 µm; n = 3). Sensilla and pore ornamentations as figured (Fig. 7 A – D ). Habitus subcylindrical, width evenly decreasing from cephalothorax to last urosomite (Fig. 7 A ). Prosome slightly shorter than urosome (including caudal rami), comprising cephalothorax and three free pedigerous somites (P 2 – P 4 - bearing somites). Naupliar eye not discernible. Integument moderately chitinized, with rectangular integumental sclerite with rounded corners dorsally on first two pedigerous somites; circular integumental windows laterally on all free pedigerous somites. Cephalothorax ~ 0.9 as long as wide and ~ 0.8 as long as prosome, with numerous sensilla. All free prosomal somites with subdistal sensilla near posterior margin.

Urosome (Fig. 7 A, B ) comprising P 5 - bearing somite, genital double-somite, two free urosomites and anal somite with caudal rami; free margins of urosomites 1–3 smooth, urosomite 4 with minute serrulation. Genital double-somite as long as wide, with ancestral articulation between both somites. Genital field as shown (Fig. 7 B ), with single small copulatory pore; one medial genital pore partly covered by P 6 fused basal plate; copulatory duct not sclerotized. Urosomites 2–4 with continuous row of spinules lateroventrally on distal margin but interrupted medially on urosomite 4; pair of cuticular pores ventrally on free urosomites 2 and 3.

Anal somite (Fig. 7 B – D ) with pair of sensilla at base of anal operculum; three or four robust spinules dorsolaterally on distal free margin continuing in row of moderate spinules laterally and ventrally; row of spinules at 1 / 2 length of somite, organized in three groups ventrally: medial and two lateral; pair of cuticular pores on anterior and posterior region of segment ventrally. Anal operculum slightly convex, not reaching tip of anal segment, with six or seven robust spinules along free margin (Fig. 7 C ).

Caudal rami (Fig. 7 B – D ) slightly divergent; subconical, ~ 1.7 × as long as wide, with cuticular pore dorsally and ventrally; with seven setae; three robust spinules dorsally, near insertion of seta VII, three laterally near insertion of seta III, two near insertion of seta VI. Seta I minute, slender, inserted just below seta II; seta II inserted at 2 / 3 length of ramus, ~ 1.5 × length of seta III; seta III inserted on distal outer corner, ~ 0.8 length of ramus; seta IV and V each with fracture plane, ~ 0.3 and 0.6 of body length, respectively; seta VI short and slender; seta VII articulate, inserted close to ramus tip on inner distal corner, ~ 1.3 × as long as ramus.

Antennule (Fig. 8 A ) eight-segmented; armament formula: I- [1], II- [9], III- [6], IV- [4 + ae], V- [2], VI- [2], VII- [4], VIII- [7 + ae]. Aesthetasc on segment IV reaching tip of ultimate segment; ae on segment VIII small and slender, as long as segment bearing it.

Antenna (Fig. 8 B ) comprising coxa, basis, one-segmented Exp, two-segmented Enp. Coxa short, unarmed. Basis unarmed, ~ 2 × as long as wide. Exp triangular, with three robust setae: proximal one spiniform, unilaterally pinnate; inner distal one spiniform, cuspid; distal one stout, pinnate. Enp- 1 ~ 2.5 × as long as wide, unarmed; Enp - 2 slightly longer than Enp- 1, with row of spinules plus one slender seta and two pinnate spines along inner margin, all short and robust; six setae apically: one setose and five geniculate setae, unequal in length; innermost geniculate seta fused to accompanying setose seta with spinules only at its base.

Mandible (Fig. 8 C ) comprising coxa, basis, one-segmented Enp. Coxal gnathobase with one robust and eight or nine unicuspid teeth ventrally; one unilaterally pinnate seta dorsally. Basis with group of filaments on tip of expansion at ~ 2 / 3 length of segment. Enp slim, ~ 2.5 × as long as wide, with five apical setae, four equal in length, one shorter.

Maxillule (Fig. 8 D ) comprising praecoxa with arthrite, coxa, basis and one-segmented Enp. Praecoxa robust, subrectangular, ~ 2 × as long as wide; praecoxal arthrite rectangular, ~ 2.5 × as long as wide, with seven elements: three robust cuspid spines apically, one subapically, one short seta ventrally; two setae equal in length on anterior surface. Coxa with cylindrical endite with one curved, unilaterally pinnate spiniform seta and one smooth seta apically. Basis with five setae apically of which outermost shortest. Enp short and minute, with two setae apically, unequal in length.

Maxilla (Fig. 8 E ) comprising syncoxa, allobasis, one-segmented Enp. Syncoxa with two endites: proximal one with a patch of filaments apically; distal one with three elements apically of which the proximalmost robust, cusped; two distal ones as smooth and slender bare setae. Allobasis drawn-out into strong claw, with one seta on caudal surface. Enp minute, ~ 1.5 × as long as wide, with two smooth setae equal in length apically.

Maxilliped (Fig. 8 F ) prehensile, three-segmented, comprising syncoxa, basis, and Enp. Syncoxa ~ 2.1 × as long as wide, with one short seta on inner distal corner. Basis ~ 2 × as long as wide, unarmed. Enp drawn-out into long robust claw, with spinules distally, minute seta near its base.

P 1 – P 4 comprised of intercoxal sclerite, praecoxa, coxa, basis, and two rami. Armament formula of P 1 – P 4 as in Table 2 .

P 1 (Fig. 9 A ) intercoxal sclerite wider than long, concave. Praecoxa triangular, with spinules along outer distal margin. Coxa parallelogram-like, with two rows of spinules on dorsal surface, one near inner margin, additional row along outer margin. Basis subtriangular, with cuticular pore on anterior surface, three rows of robust spinules of which inner at base of inner spine, median between insertion of rami, outer along the outer margin; inner and outer spines pinnate, inner spine reaching proximal third of Enp- 1. All Exp segments with row of spinules along outer margin and on outer distal corner; Exp- 1 ~ 1.8 × as long as wide, with outer spine as long as segment bearing it. Exp - 2 ~ 1.8 × as long as wide with inner seta and outer spine as long as segment bearing them. Exp - 3 ~ 1.8 × as long as wide with one unipinnate seta, two geniculate setae unequal in length apically; outer spine as long as segment bearing it. Enp well surpassing tip of Exp. Enp- 1 ~ 2.5 × as long as wide, well overreaching mid of Exp - 2. Enp - 2 ~ 2.5 × as long as wide, with row of spinules along outer margin. Enp - 3 ~ 3 × as long as wide, ~ 1.5 × as long as Enp - 2, with row of spinules along outer margin, with three elements: a slender seta subapically on inner margin, and a geniculate seta and a spine apically.

P 2 (Fig. 9 B ) intercoxal sclerite as in P 1 but larger. Praecoxa triangular, bare. Coxa trapezoidal, bare. Basis as in P 1 but lack medial spine, with two rows of spinules, one along outer margin, one between insertion of Exp and Enp. Exp- 1 ~ 1.5 × as long as wide, outer spine as long as segment bearing it, robust. Exp - 2 ~ 1.5 × as long as wide, with inner seta and outer spine ~ 1.7 × longer than segment bearing them. Exp - 3 ~ 3 × as long as wide; three elements apically: one plumose seta, one plumose on one side and pinnate on other side, outer unipinnate seta as long as segment bearing it. Enp reaching 3 / 4 length of Exp - 2. Enp- 1 as long as wide, bare, with acute extension on distal inner corner. Endp- 2 ~ 2.5 × as long as wide; inner apical plumose seta longer than Enp; outer apical spine robust, shorter than segment bearing it.

P 3 (Fig. 9 C ) as in P 2 but basis with long bare seta on outer margin; Enp - 2 with robust spinules on both margins.

P 4 (Fig. 9 D ) intercoxal sclerite, praecoxa, coxa, basis, and two proximal Exp segments as in P 3, with relatively shorter lateral seta on basis. Exp - 3 ~ 3.5 × as long as wide; along inner margin two spiniform setae unequal in length, longer one ~ 1.5 × length of segment bearing it; one plumose seta, other one plumose on one side and pinnate on other side, equal in length apically; outer spine apically shorter than segment bearing it; outer lateral spine short. Enp as in P 3, but relatively slender, just reaching proximal margin of Exp - 2.

P 5 (Fig. 9 E ) with baseoendopod completely incorporated into somite, with long bare slender seta on outer margin; one segmented Exp. Exp elliptical, ~ 2 × as long as wide; inner seta ~ 2 × as long as outer one; two smooth setae apically; one smooth seta on outer margin.

P 6 (Fig. 7 B ) reduced, represented by fused basal plate; on both sides one minute seta and knob-like extension on distolateral margin.

Description of adult male.

Total body length, excluding caudal setae, 564 and 562 µm (n = 2). Sensilla and pore ornamentation as figured (Fig. 10 A, B ). Prosome as long as urosome (Fig. 10 A ). Naupliar eye and integument ornamentation as in female. Cephalothorax ~ 0.9 × as long as wide, ~ 1 / 2 length of prosome, with numerous sensilla. Other characteristics of prosoma somites as in female, but presence of continuous row of spinules on urosomite 5 ventrally (Fig. 10 B ).

Urosome (Fig. 10 A, B ) comprising P 5 - bearing somite, genital somite, three free urosomites and anal somite with caudal rami; free margins of urosomites 1–4 smooth, urosomite 5 with minute serrulation. P 5 - bearing somite as in female. Genital somite with three pairs of subdistal sensilla dorsally, ~ 1 / 2 as long as wide (Fig. 10 A, B ). Three subsequent urosomites, anal somite, caudal rami, and anal operculum as in female.

Antennule (Fig. 10 C ) ten-segmented, geniculate; geniculation between segments VII and VIII. Armament formula: I- [1], II- [10], III- [6], IV- [1], V- [8 + ae], VI- [1], VII- [2], VIII- [1], IX- [4], X- [7 + ae]. Aesthetasc on segment V large, well over-rich tip of antennule; that of ultimate segment small and slender.

Antenna and mouthparts as in female.

P 1 (Fig. 11 A, B ) as in female, but basis with complex hook-like transformed seta on inner margin.

P 2, P 3, and P 4 as in female, but P 3 Enp - 2 (Fig. 11 C ) with large outer spine and short inner seta apically.

P 5 (Fig. 11 G ) with baseoendopod completely incorporated into somite with long, bare slender seta on outer margin; one segmented Exp. Exp elongated, ~ 3 × as long as wide, with one smooth seta on inner margin, two smooth setae apically, outer seta as long as outer one.

P 6 (Fig. 10 B ) left and right leg form simple plate, asymmetrical, bare, with smooth distal margins. Right leg reduced into simple plate, operculiform; left leg completely incorporated into somite.

Variability.

The “ allotype ” bears an additional pinnate seta on the inner margin on the right P 4 Enp - 2 (Fig. 11 D ) and an additional inner seta on the right P 5 Exp apically (Fig. 11 G ) compared with relevant left-side swimming legs.

Etymology.

The specific name is formed from Thailand, alluding to the name of the country where the new species was discovered. The name is an adjective in the nominative singular, gender feminine.

Figures

Figure 7. Nitocrella thailandensis sp. nov., female holotype: A habitus, dorsal view B urosome, ventral view C urosomite 4, anal somite and caudal rami, dorsal view D urosomite 4, anal somite and caudal rami, lateral view. Arrows indicate integumental pores. Scale bars: 50 μm.

Figure 8. Nitocrella thailandensis sp. nov., female holotype: A antennule B antenna C mandible D maxillule E maxilla F maxilliped. Arrowheads indicate aesthetascs. Scale bars: 50 μm.

Figure 9. Nitocrella thailandensis sp. nov., female holotype: A P 1 B P 2 C P 3 D P 4 E P 5. Scale bars: 50 μm.

Figure 10. Nitocrella thailandensis sp. nov., male “ allotype ”: A habitus, dorsal view B urosome, ventral view C antennule. Arrows and arrowheads indicate integumental pores and aesthetascs, respectively. Scale bars: 50 μm.

Figure 11. Nitocrella thailandensis sp. nov., male “ allotype ”: A right P 1 B P 1 basis with complex hook-like transformed seta C P 3 Enp D right P 4 Enp E left P 4 Enp F left P 5 G right P 5. Scale bars: 50 μm.