Nitocrella grandicaudis, 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 grandicaudis sp. nov.

Figs 2 , 3 , 4 ( female); Figs 5 , 6 (male )

Type material.

Holotype: Thailand • 1 ♀ (adult), 470 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 the mouth of a karstic spring; access number: THNHM-IV-20713 ; completely dissected, mounted on a slide in glycerol, covered with a coverslip and sealed with nail polish . Paratype 1 (“ allotype ”): Thailand • 1 ♂ (adult), 431 μm long; location, date, and collectors as for holotype; access number: THNHM-IV-20714 ; 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-20715 ; 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 463 µm to 472 µm (mean = 469 µm; n = 3). Sensilla and pores ornamentations as figured (Fig. 2 A – C ). Habitus subcylindrical, width evenly decreasing from cephalothorax to last urosomite (Fig. 2 A, B ). Prosome as long as 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 ~ 1.1 × as long as wide and ~ 1 / 2 as long as prosome, with numerous sensilla dorsally. P 2 – P 4 - bearing somites with free margin smooth; each with pair of sensilla near posterior margin dorsally.

Urosome (Fig. 2 A – C ) comprising P 5 - bearing somite, genital double-somite, two free urosomites (urosomites 3 and 4) and anal somite with caudal rami; free margins of urosomites 1–3 smooth, urosomite 4 with minute serrulation dorsally. Genital double-somite as long as wide, with ancestral articulation between both somites (Fig. 2 A – C ). Genital field as shown (Fig. 2 C ), with single small copulatory pore and one median genital pore covered by P 6 fused basal plate; copulatory duct not sclerotized. Urosomites 2 and 3 with continuous row of spinules ventrolaterally on distal margin; a pair of cuticular pores ventrally (Fig. 2 B, C ). Urosomite 4 lack row of spinules and cuticular pore; with serrated hyaline free margin distally. Anal somite (Fig. 2 C – E ) with pair of sensilla at base of anal operculum, with robust spinules on distal margin lateroventrally; three groups of spinules on each side ventrally and ventrolaterally; two rows near anterior margin, distal one near caudal ramus. Anal operculum slightly convex, with row of ~ 15 small spinules dorsally along free margin.

Caudal rami (Fig. 2 C – F ) slightly divergent; semi-elliptical, ~ 1.7 × as long as wide, with large dorsal keel and seven setae; with row of few spinules near insertion of seta III, seta VI, and seta VII, respectively; one cuticular pore dorsally and ventrally. Seta I minute, slender, inserted next to seta II; seta II inserted at 3 / 4 length of ramus, ~ 1 / 2 length of seta III; seta III inserted on distal outer corner; 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.

Antennule (Fig. 3 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 reach tip of ultimate segment; that on segment VIII small and slender.

Antenna (Fig. 3 B ) comprising coxa, basis, one-segmented Exp, two-segmented Enp. Coxa short, unarmed. Basis with row of spinules along inner margin, ~ 2 × as long as wide. Exp elongated, with three setae: proximal one spiniform, slender, unilaterally pinnate; inner distal one spiniform, cusped; outer distal one soft, pinnate. Enp- 1 ~ 2.5 × as long as wide, unarmed; Enp - 2 club-shaped, slightly longer than Enp- 1, with row of spinules, one slender seta and two pinnate spines along inner margin; six setae apically: one setose, five geniculate; innermost geniculate seta fused to accompanying seta, with spinules only at its base.

Mandible (Fig. 3 C ) comprising syncoxa, basis, one-segmented Enp. Coxal gnathobase with two 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, ~ 3 × as long as wide, with five setae apically, decreasing in length.

Maxillule (Fig. 3 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 cusped spines apically, one spine subapically, one short seta ventrally, two setae equal in length on anterior surface. Coxa with cylindrical endite with one curved spiniform seta and one smooth seta apically. Basis with five setae of which outermost shortest, apically. Enp short and minute, with two setae of which shortest one pilose, apically.

Maxilla (Fig. 3 E ) comprising syncoxa, allobasis, one-segmented Enp. Syncoxa with two endites: proximal endite with several filaments apically; distal endite 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 short, minute, with two smooth setae equal in length apically.

Maxilliped (Fig. 3 F ) prehensile, three-segmented, comprising syncoxa, basis and Enp. Syncoxa ~ 3 × as long as wide, with one short seta on inner distal corner. Basis ~ 2 × as long as wide, unarmed. Enp drawn-out into strong claw, unilaterally pinnate distally, with minute seta near 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 1 .

P 1 (Fig. 4 A ) intercoxal sclerite wider than long, concave. Praecoxa triangular, with spinules along outer 1 / 2 of margin distally. Coxa parallelogram-like, with two rows of spinules on dorsal surface, one near inner margin, additional row along outer margin; unarmed. Basis subtriangular, with cuticular pore on anterior surface; three rows of robust spinules distally of which outermost at base of Exp, median between insertion of rami, inner at base of inner spine; outer and inner spines short, robust, pinnate, similar in length. All segments of Exp with row of spinules along outer margin and outer distal corner. Exp- 1 ~ 1.5 × as long as wide, outer spine as long as segment bearing it. Exp - 2 ~ 1.5 × as long as wide; outer spine robust, as long as segment bearing it, inner seta slightly longer than segment bearing it. Exp - 3 ~ 1.5 × as long as wide, with two geniculate and one unilaterally pinnate seta apically, unilaterally pinnate spine on outer margin as long as segment bearing it. Three-segmented Enp well surpass tip of Exp - 3; Enp- 1 ~ 2.5 × as long as wide, reaching 1 / 2 length of Exp - 2; row of setules along inner margin. Enp - 2 ~ 2.5 × as long as wide, with row of spinules along outer margin. Enp - 3 as long as Enp - 2, with row of spinules along outer margin, armed with three elements: innermost slender seta as long as segment bearing it, median geniculate seta long, outermost spiniform seta unilaterally pinnate, ~ 1 / 2 length of geniculate one.

P 2 (Fig. 4 B ) intercoxal sclerite as in P 1, but slightly larger. Praecoxa triangular, bare. Coxa trapezoidal, bare. Basis as in P 1 but lack medial spine; row of spinules along outer margin. Three-segmented Exp with spinules ornamentation as in P 1. Exp- 1 ~ 2 × as long as wide. Exp - 2 ~ 2.1 × as long as wide, inner seta and outer spine as long as segment bearing them. Exp - 3 ~ 4 × as long as wide, with four elements: two long plumose setae, unequal in length and one unilaterally pinnate spine, as long as segment bearing it apically; lateral unipinnate spiniform seta shorter than segment bearing it on outer margin. Two-segmented Enp reaching proximal third of Exp - 2, with spinules along outer margin on both segments; Enp- 1 ~ 1.3 × as long as wide, bare, with acute extension on distal inner corner. Enp - 2 ~ 2 × as long as wide, with two elements apically: inner seta long, plumose; outer one smooth spine, as long as segment bearing it.

P 3 (Fig. 4 C ) as in P 2, but basis with long bare seta on outer margin.

P 4 (Fig. 4 D ) intercoxal sclerite, praecoxa, coxa, basis, and two proximal Exp segments as in P 3, but relatively shorter seta on basis on outer margin. Exp - 3 with five elements: spine on outer margin relatively thin, shorter than segment bearing it; two plumose setae unequal in length and unilaterally pinnate seta apically; seta on inner margin smooth. Enp as in P 2 and P 3, but relatively slender, reaching distal margin of Exp - 2 at most; Enp- 1 ~ 2 × as long as wide; Enp - 2 as in P 2 and P 3 but with robust spinules on inner and outer margin.

P 5 (Figs 2 C , 4 E ) with baseoendopod completely incorporated into somite with long, smooth slender seta on outer margin; one-segmented Exp. Exp elliptical, ~ 3 × as long as wide, with one smooth seta on outer margin; two smooth setae apically, inner seta slightly longer than outer one.

P 6 (Fig. 2 C ) reduced, represented by fused basal plate; on both sides with one minute seta and knob-like extension on distolateral margin.

Description of adult male.

Total body length, excluding caudal setae, 428 and 431 µm (mean = 430 µm; n = 2). Sensilla and pore ornamentations as figured (Fig. 5 A, B ). Prosome as long as urosome (Fig. 5 A ). Naupliar eye and integument as in female. Cephalothorax ~ 1.1 × as long as wide and ~ 1 / 2 length of prosome, with numerous sensilla. Other characteristics of prosoma somites as in female.

Urosome (Fig. 5 A, B ) comprising P 5 - bearing somite, genital somite, three free urosomites and anal somite with caudal rami; free margins of all somites smooth dorsally. P 5 - bearing somite as in female. Genital somite with three pairs of subdistal sensilla dorsally (Fig. 5 A ). Three subsequent urosomites, anal somite and anal operculum as in female.

Caudal rami (Fig. 5 B, C ) sexually dimorphic, slightly divergent, subconical, ~ 2.5 × as long as wide; ornamentation as in female but without dorsal keel.

Antennule (Fig. 6 A ) ten-segmented, geniculate, with 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- [8 + ae]. Segment V with proximalmost inner seta modified into strong curved spiniform element. Aesthetasc on segment V long, reaching beyond tip of segment X of antennule.

Antenna, mandible, maxillule, maxilla, and maxilliped as in female.

P 1 (Fig. 6 B ) as in female, but basis with complex hook-like transformed seta on inner margin (Fig. 6 C ).

P 2 as in female, except with relatively larger outer spine apically on Enp - 2 (Fig. 6 D ).

P 3 as in female, but Enp - 2 with robust outer pinnate spine, longer than segment bearing it and shorter inner seta with feather-like tip apically (Fig. 6 E ).

P 4 (Fig. 6 F ) and P 5 (Fig. 5 D, E ) as in female.

P 6 (Fig. 5 B ). Left and right legs form simple plate, unarmed, with smooth distal margin; asymmetrical; right leg reduced into simple plate, operculiform; left leg completely incorporated into somite.

Variability.

The “ allotype ” right P 5 Exp with an additional plumose seta on the inner margin (Fig. 5 E ) is present, but absent in left P 5 (Fig. 5 D ).

Etymology.

The specific name is an allusion to a ridge on the dorsal side of a female caudal ramus, producing a high lateral profile. The name is an adjective in the nominative singular, feminine gender.

Figures

Figure 2. Nitocrella grandicaudis sp. nov., female holotype: A habitus, dorsal view B habitus, lateral view C urosome, ventral view; (arrows and arrowheads indicate integumental pores and copulatory pore, respectively) D anal somite and caudal rami, dorsal view E anal somite and caudal rami, lateral view (asterisk indicates caudal seta I) F left caudal ramus with indication of setation. Arrow indicates integumental pore. Scale bars: 100 μm (A, B); 50 μm (C – F).

Figure 3. Nitocrella grandicaudis sp. nov., female holotype: A antennule B antenna C mandible D maxillule E maxilla F maxilliped. Arrowheads indicate aesthetascs. Scale bars: 50 μm.

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

Figure 5. Nitocrella grandicaudis sp. nov., male “ allotype ”: A habitus, dorsal view B urosome, ventral view C anal somite and caudal rami, lateral view D left P 5 E right P 5. Arrows indicate integumental pores. Scale bars: 50 μm (B – E).

Figure 6. Nitocrella grandicaudis sp. nov., male “ allotype ”: A antennule (arrowheads indicate aesthetascs) B P 1 C P 1 basis with complex hook-like transformed seta D P 2 Enp E P 3 Enp F P 4. Arrowheads indicate aesthetascs. Scale bars: 50 μm.