Nitokra quangnamensis, Tran & Trinh-Dang & Nguyen & Brancelj, 2025

Tran, Ngoc-Son, Trinh-Dang, Mau, Nguyen, Thi Tuong Vi & Brancelj, Anton, 2025, A new species of Nitokra Boeck, 1865 (Copepoda: Harpacticoida: Ameiridae) from a hyporheic zone in central Vietnam, Zootaxa 5590 (1), pp. 46-60 : 48-55

Nitokra quangnamensis sp. nov.

urn:lsid:zoobank.org:pub:14DA67D3-739C-41E9-A6FD-7BFAC986487

( Figs. 2–8 )

Type locality. Hyporheic zone on a bank of the Vugia-Thubon River , Tien Phuoc district, Quang Nam province, central Vietnam; coordinates: 15° 29’ 12.3” N, 108° 18’ 14.6” E; altitude: 50 m a.s.l. ( Fig.1 ).

Material examined. Holotype: one adult female, total body length, excluding caudal setae, 556 µm, completely dissected, mounted in glycerol on a slide and sealed with nail polish (access No: ZC-DTU-COPEPODA-0011). Collected on 12 March 2023 by Ngoc-Son Tran, Mau Trinh-Dang, Thi Tuong Vi Nguyen . Allotype: male, total body length, excluding caudal setae, 510 µm, completely dissected, mounted on one slide (access No: ZC-DTU- COPEPODA-0012) . Paratypes: three males, ten females, stored in 70 % alcohol (access No: ZC-DTU-COPEPODA-0013) . Allotype and paratypes collected on the same date and location as holotype. Type material deposited at the Zoological Collection of Duy Tan University ( ZC-DTU), Da Nang city, Vietnam.

Diagnosis of new species. Nitokra with morphological characters consistent with Group III (sensu Gomez et al. 2012) except for P5 Exp with 7 setae and P1 Enp-1 reaching 1/2 of the length of P1Exp-3.

Etymology. The new species N. quangnamensis sp. nov. is named after Quang Nam province, where it was found for the first time.

Description of adult female holotype: body length, measured from anterior tip of rostrum to a tip of caudal rami, 525–594 µm (mean = 558 µm, n = 3) ( Fig. 2A ). Habitus slender, cylindrical in shape, tapering posteriorly, inconspicuous boundary between prosome and urosome; no dorsal hyaline window; the largest width at distal margin of cephalothorax. Body colorless in preserved specimens, naupliar eye not discernible. Rostrum well developed, overreaching first antennules segment, with two sensilla on distal margin. Prosome 4-segmented, consists of cephalothorax and three free pediger somites. Genital double-somite with fused first and second abdominal somite; genital aperture relatively short, cylindrical ( Fig. 1G ). Genital double-somite and two consecutive somites with continuous row of small spinules ventrally and dorsolaterally. Anal somite ( Figs. 2A–D ) with short row of spinules and sensillum on each side of base of anal operculum; row of strong spinules along free margin of segment dorsolaterally. Anal operculum ( Figs. 2A, B ) slightly convex, with six strong spines along hyaline free margin. Furcal rami ( Figs. 2C–D ) slightly divergent; each ramus subquadrate, about 1.2 times l/w, with seven elements each. Anterolateral accessory seta (I) slender, short, about 1/3 as long as caudal ramus; anterolateral seta (II) and posterolateral seta (III) smooth; seta II about twice as long as seta I; seta III about 2.3 times as long as caudal ramus; outer terminal seta (IV) long, strong, plumose, with fracture plane; inner terminal seta (V) strong, longest, at base with few spines, with fracture plane; terminal accessory seta (VI) slender, smooth, as long as outer apical seta; dorsal seta (VII) articulated, about 1.5times as long as caudal ramus.

Antennule ( Fig. 3A ): eight-segmented, not reaching middle of cephalothorax. Aesthetasc on segment IV overreaching tip of segment VIII; aesthetasc on the last segment shorter and slimmer than aesthetasc on segment IV; both aesthetascs fused with seta at its base (forming acrothek). Setal formula: 1, 9, 6, 3+ae, 3, 3, 3, 4+ ae.

Antenna ( Fig. 3B ): comprising coxa, allobasis, one-segmented Exp. and Enp. Allobasis about four times l/w, with several spinules at 1/3 length along median margin. Exp. short, with two smooth unequally long setae apically, one unipinnate seta subapically. Enp. as long as allobasis, with two strong spines on distal inner margin, row of fine spinules along inner margin; four geniculate setae unequal in length apically, accompanied with unipinnate slender seta.

Mandible ( Fig. 3C ): comprising coxa, basis, Exp. and Enp.; gnathobase with row of sharp chitinized teeth decreasing in size, accompanied with single seta on distal corner. Enp. represented with robust plumose seta. Exp. with smooth seta laterally, five smooth setae apically.

Maxillule ( Fig. 3D ): praecoxa with three strong curved spines on arthrite; inner margin with spiniform seta; dorsal surface with two small spines. Coxa with two unipinnate spines. Baseoendopod with five smooth setae apically, unequally long. Exp. minute, two-segmented, with two setae apically on distal segment, unequal in length.

Maxilla ( Fig. 3E ): short, robust; syncoxa with endite armed with two apical setae, one subapical. Basis with claw and strong smooth seta. Enp. small, one-segmented, with two long smooth setae apically.

Maxilliped ( Fig. 3F ): prehensile; syncoxa with plumose seta subapically, representing epipodite; two rows of strong spinules transversally at 1/2 and 3/4 length of a segment. Basis about three times l/w, bare. Enp. drawn into unipinnate claw, curved inwards; with bare thin seta at its base.

P1–P4: with three-segmented Exp. and Enp. P1, P3, P4 intercoxal sclerites (couplers) with convex free margin, without ornamentation; P2 couplers with row of strong spinules on each lobe distally. Coxa of P1–P4 with several rows of spinules of different length; number of rows decrease from P1 to P4.

Armature formula of P1–P4 as follows (legend: inner-outer seta/spine; inner-apical-outer seta/spine; Arabic numerals represent setae, Roman numerals represent spines):

* In some specimens inner seta could be absent on left/right leg.

P1 ( Fig. 4A ): shorter than other legs. Basis with strong, robust spine on inner and outer margin, accompanied with several rows of spinules. Exp. shorter than Enp. Exp-1–Exp-3 slightly longer than wide, with several robust spinules along outer margin; Exp-1 and Exp-2 with robust spine on outer margin, longer than segment bearing it. Exp-3 with two geniculate setae apically, unequal in length. Enp-1 reaching approximately middle of segment of Exp-3, with relatively long plumose seta at 1/2 length of inner margin; few robust spinules on distal margin. Enp-2 with thin plumose seta inserted subdistally on inner margin; Enp-3 with robust unipinnate seta, long geniculate seta, slender seta apically.

P2 ( Fig. 4B ): basis with short, robust spine on outer margin, with row of spinules on distal outer and medial margins. Exp-1 and Exp-2 about 1.2 times l/w, with several robust spinules along outer margin; each segment with robust spine on outer margin, longer than segment bearing it. Exp-3 about 3.5 times l/w, with unipinnate spine and bipinnate seta apically; outer margin with three robust spines, increasing in length along the margin distally. Enp. tip reaching 1/4 length of Exp-3 segment. Enp-1 as long as wide, Enp-2 about 1.2 times l/w, Enp-3 about 2.5 times l/w, with long bipinnate inner seta apically, middle seta half-length of inner seta, outer seta spiniform, short, bare.

P3 ( Fig. 5A ): basis with unipinnate seta on outer margin, accompanied with a row of robust spinules on distal outer and medial margin. Exp-1 about 1.5 times l/w, with stout spine on distal outer corner. Exp-2 twice l/w, with spine as long as segment bearing it, with several robust spinules along outer margin; plumose seta on inner margin, shorter than segment bearing it. Exp-3 about 3.5 times l/w, with unipinnate spine and plumose seta similar in length apically; outer margin with three robust spines increasing in length distally. Enp. tip slightly overreaching tip of Exp-2. Enp-1 as long as wide, Enp-2 about 1.5 times l/w, Enp-3 about 3 times l/w, three elements apically: three long plumose setae unequal in length, outer seta shortest, about 2/3 of medial setae length. Short bare spiniform seta on outer margin subapically.

P4 ( Fig. 5B ): basis with smooth outer seta, accompanied with row of robust spinules at base. Exp-1 about 1.5 times l/w, with spine at distal outer corner and several spinules along outer margin. Exp-2 about three times l/w, with several spinules along outer margin; spine on distal outer corner shorter than segment bearing it; inner seta plumose, shorter than segment bearing it. Exp-3 about four times l/w, with unipinnate spine and plumose seta apically, similar in length; sub-apical inner seta robust, longest, bipinnate; outer margin with three robust spines, increasing in length along margin distally. Enp. tip reaching tip of Exp-2. Enp-1 as long as wide; Enp-2 about twice l/w, each with short plumose seta on inner side. Enp-3 about four times l/w, with three plumose setae and short spine apically, middle seta longest. Inner seta at 1/2 length of segment, long, unipinnate.

P5 ( Fig. 2E ): left and right leg well separated; Exp. and baseoendopod well separated; baseoendopod reach mid-length of Exp., with four elements: two short inner smooth spiniform setae unequally long; two outer plumose spiniform setae, inner one longer; outer seta bare, spiniform, articulated. Exp. semioval, with seven elements: innermost bipinnate seta, as long as Exp.; seta next to it twice as long as inner one, bare, slim, accompanied with short slim seta; spiniform bipinnate seta on outer corner apically; three smooth setae along outer margin, unequal in length. Short row of minute spinules on distal inner margin.

P6 ( Fig. 2F ): simple, represented by one short plumose seta.

Description of male allotype: body length, measured from anterior margin of rostrum to posterior margin of caudal rami, 496–543 µm (mean = 516 µm, n = 3). Habitus slender, cylindrical in shape, tapering posteriorly, well defined boundary between prosome and urosome, the largest width at distal margin of cephalothorax; no dorsal hyaline window ( Fig. 6A ). First abdominal somite (genital somite) about twice l/w, with circumventral row of small spinules on distal margin. Rostrum ( Fig. 6A ), fucal rami ( Figs. 6A–D ), operculum ( Fig. 6C ), antenna, mouthparts, P1–P4 as in female, but modified spine on inner margin of coxa of P1 ( Fig. 8A ).

Antennule( Fig.7A ):subchirocerate,eight-segmented;aesthetasconsegmentIVwelldeveloped,welloverreaching last antennule segment; aesthetasc on segment VIII thin, relatively short; both form acrothek. Segment I with plumose seta, segment IV with short spiniform pinnate seta. Setal formula as follows: 1.6.6.1+1ae.1.1.1.7+1ae.

P1 ( Fig. 8A ): as in female, but inner spine of basis modified in element with rounded tip.

P5 ( Fig. 7B ): left and right leg fused; Exp. and baseoendopod well separated; baseoendopod about 1/2 length of Exp., with three bare setae decreasing in length from inner to outer position. Exp. with six bare setae, unequal in length; outermost seta longest, about twice as long as segment bearing it; innermost seta strong, shortest.

P6 ( Fig. 7C ): represented by two smooth setae, unequal in length; inner seta longer than outer one.

Variability. Absence of inner seta on P4 Enp- 3 in some females.

Remarks. Nitokra quangnamensis sp. nov. differs from N. vietnamensis Tran & Chang, 2012 , both described from Vietnam, in characters as follows: i) the new species have the distal segment of mandibular palp with six elements but four in N. vietnamensis ; ii) the new species has two setae on the maxillule coxa but three in N. vietnamensis ; iii) female P5 Exp. in the new species has l/w ratio about 1.1 times but about three times in N. vietnamensis ; iv) female P5 baseoendopod in the new species has four setae but five in N. vietnamensis ; v) female P5 Exp. in the new species has seven setae but six in N. vietnamensis ; vi) tip of P1 Enp-1 of the new species extends to about 1/2 length of P1 Exp-3, but to 1/3 length of P1 Exp- 3 in N. vietnamensis .

Figures

FIGURE 1. Maps of the sampling location of the new Nitokra species, N. quangnamensis sp. nov. in Tien Phuoc district, Quang Nam province, Vietnam.

FIGURE 2. Nitokra quangnamensis sp. nov. Female, holotype: A—habitus, dorsal view; B—urosome, dorsal view; C— rosome, ventral view; D—urosome, lateral view; E—P5; F—P6; G—genital complex.

FIGURE 3. Nitokra quangnamensis sp. nov. Female, holotype:A—antennule; B—antenna; C—mandible; D—maxillule; E— maxilla; F—maxilliped.

FIGURE 4. Nitokra quangnamensis sp. nov. Female, holotype: A—P1; B—P2 left; C—P2 Enp—right.

FIGURE 5. Nitokra quangnamensis sp. nov. Female, holotype: A—P3; B—P4.

FIGURE 6. Nitokra quangnamensis sp. nov. Male, allotype: A—habitus, dorsal view; B—urosome, lateral view; C—urosome, dorsal view; D—urosome, ventral view.

FIGURE 7. Nitokra quangnamensis sp. nov. Male, allotype: A—antennule; B—P5 and P6.

FIGURE 8. Nitokra quangnamensis sp. nov. Male, allotype: A—P1; B—P2.