Tropodiaptomus kampucheaensis Koompoot & Sanoamuang, 2025, sp. nov.

Tropodiaptomus kampucheaensis sp. nov. Figs 10, 11, 12, 13, 14, 15, 16 Tropodiaptomus sp.: Chaicharoen and Sanoamuang (2022): 1, 6, 7, 9, 11, 12, 13. Material examined. Holotype: Cambodia • one ♂ (adult), Cambodia, Kampong Cham Province, Tbong Khmum District, 12°32'34"N, 105°36'94"E; 16 June 2006; water temperature 28.9 ° C, pH 7.7, and conductivity 108.6 µS cm - 1. W. Mahasrap leg.; a rice field (Fig. 1); accession number: THNHM -lv-19360; dissected, mounted on one slide in glycerol, covered with a coverslip, and sealed with nail polish. Allotype: Cambodia • one ♀ (adult); location, date and collectors as for holotype; accession number: THNHM -lv-19361, completely dissected, mounted on one slide in glycerol, covered with a coverslip, and sealed with nail polish. Paratypes: Cambodia • three ♂ (adult) and three ♀ (adult); date and collectors as for holotype; accession number: THNHM -lv-19362, undissected and preserved in 70 % ethanol. Additional occurrence locality. A temporary roadside canal, Kandal province, Cambodia (11°38'72"N, 104°20'19"E); 16 June 2006; water temperature 29.2 ° C, pH 8.2, and conductivity 94.1 µS cm - 1. Description of adult male. Total body length, measured from anterior margin of rostrum to posterior margin of caudal rami, 0.94–0.95 mm (mean 0.947 mm, n = 3) (Figs 10 A, 12 A). Body smaller and slender than in female. Prosome ~ 2.5 × as long as urosome (Fig. 10 A, 12 A). Pdg 4 separated dorso-laterally from Pdg 5. Lateral wings of Pdg 5 small, symmetrical, with one tiny spine at distal corner and one inner sensillum-like spine (Figs 10 C, 12 B). Urosome (Figs 10 A – C, 12 A – C) with five somites, unornamented. Genital somite dilated postero-laterally on both sides (Fig. 12 C), shorter than wide. Urosomite 2 ~ as long as wide, urosomites 3 and 4 shorter than wide. Urosomites 2 and 3 without hairs on ventral side (Figs 10 B, 12 C). Urosomite 4 with expanded right dorso-posterior margin. Anal somite asymmetrical, left side slightly longer than right side. Caudal rami symmetrical, each ramus ~ 1.5 × as long as wide, inner margins hairy (Fig. 12 C). Ventral surfaces of both caudal rami without any prominent structures. Each ramus armed with five plumose setae and one base dorsal seta. Antennules: asymmetrical, long, reaching to posterior end of genital somite. Left antennule (Fig. 13 A): 25 - segmented. Armature formulae as in Table 4. Right antennule geniculated (Figs 10 D, 12 E – G), consisting of 22 segments, strongly dilated between segment XIII and segment XVIII. Segment XIII with largest strong spinous process, one seta, and one aesthetasc. Antepenultimate segment (segment XX) longer than next segment. Spinous process on antepenultimate segment straight with an outwardly curved tip, reaching 2 / 3 of next segment (Figs 10 D, 12 G). Armature formulae as in Table 5. Antenna (Fig. 13 B) biramous. Coxa and basis with one and two bare setae on distal corner, respectively. Enp two-segmented; Enp - 1 with two inner median setae and small spinules on distal outer margin; Enp - 2 bilobed, bearing eight setae on inner lobe and six setae on outer lobe. Exp seven-segmented, longer than Enp. Exp 1–6 with setal formulae 1, 3, 1, 1, 1, and 1, respectively. Exp 7 with one inner seta and three apical setae. Mandible (Fig. 13 C): coxal gnathobase with cutting edge bearing eight well-chitinized teeth and one setulose seta. Basis with four inner setae; one located proximally and three distally. Enp two-segmented; Enp - 1 with four setae on inner distal corner; Enp - 2 with eight setae apically. Exp four-segmented; Exp - 1–3 each with one seta on inner margin; Exp - 4 with three setae apically; all setae bare. Maxillule (Fig. 13 D): precoxal arthrite with nine strong setae laterally, four slender submarginal setae, and one anterior seta. Coxal epipodite with nine setae; coxal endite with four setae. Basal endites each with four setae proximally and four setae distally; basal exite with one outer seta. Enp with eight setae distally. Exp with six setae. Maxilla (Fig. 13 E): praecoxa fused to coxa. Proximal and distal endites on praecoxa each with three setae apically. Two coxal endites each with three setae apically. Allobasis with three setae apically. Enp two-segmented, each with three setae. Maxilliped (Fig. 13 F) praecoxa and coxa fused, three medial lobes on syncoxa: setal formulae 2, 3, 3, respectively; subdistal inner margin produced into a spherical lobe with a patch of tiny spinules. Basis with three setae at distal inner margin, with a row of tiny spinules proximately. Enp six-segmented, with 2, 3, 2, 2, 1 + 1, and 4 setae, respectively. Swimming legs (P 1 – P 4) (Fig. 14 A – D) biramous, with three-segmented rami, except for two-segmented Enp on P 1. Exp longer than Enp. Each coxa on P 1 – P 4 with one pinnate seta at innermost distal corner. P 4 coxa with an extraordinarily long inner seta (Fig. 14 D). P 1 and P 2 bases without setae. P 3 and P 4 bases with a bare outer seta. P 2 Enp - 2 with a Schmeil’s organ on posterior surface (Fig. 14 B). Armature formulae of P 1 – P 4 as in Table 6. P 5 (Figs 11 A – F, 12 D) highly asymmetrical. Intercoxal sclerite reduced, inner distal margin not produced. Coxae fused to intercoxal sclerite. Right P 5 (Figs 11 A – C, F, 12 D): right coxa larger than left one, with a triangular spine on outer subdistal corner of posterior surface. Basis (Figs 11 A, B, F, 12 D) rectangular, ~ 1.5 × as long as wide, ornamented with a thin, longitudinal hyaline membrane located at mid-length of inner margin (Figs 11 B, 12 D), and a short seta at subdistal outer corner. Exp - 1 (Figs 11 A – C, 12 D) shorter than wide, produce into acute process on outer distal corner. Exp - 2 (Figs 11 A, C, 12 D) elongated, somewhat rectangular, ~ 1.9 × as long as wide, with a thin crescent-shaped lamella near base of principal lateral spine (Figs 11 C, 12 D). Principal lateral spine robust, slightly curved, acutely pointed, ~ 0.9 × as long as Exp - 2 segment, located sub-distally, close to end claw, with spinules on distal outer and inner margins. End claw long, slender, and sickle-shaped, with a pointed tip and ornamented with spinules on inner margin; ~ 1.6 × as long as Exp - 2. Enp one-segmented, conical, reaching of Exp - 1, and bearing a row of apical spinules. Left P 5 (Figs 11 A, B, D, E, 12 D) slightly bent inwards, reaching to 1 / 4 of right Exp - 2. Coxa as long as wide, with one triangular spine inserted on posterior lobe, at mid-distal outer margin. Basis (Figs 11 B, 12 D) rectangular, elongated, ~ 1.6 × as long as wide, with one short seta near outer corner distally; inner margin straight, without hyaline lamella. Exp (Fig. 11 D, E) flattened, elongated, ~ 1.0 × as long as basis; inner margin one-lobed, with uniform serration; anterior surface ornamented with two hairy pads in center, proximal one located under Enp; apex of Exp with usual combination of digitiform appendix and spinulate seta. Enp (Fig. 11 E) one-segmented, slightly cylindrical, extending to mid-length of Exp; apex rounded with a row of subapical spinules. Description of adult female. Total body length, measured from anterior margin of rostrum to posterior margin of caudal rami, 1.53–1.55 mm (mean 1.54 mm, n = 3). Prosome: urosome ratio ~ 2.3: 1. Prosome similar to that of male. Rostrum (Fig. 15 B) symmetrical, with moderate strong and acutely pointed, paired filaments. Pdg 4 and Pdg 5 completely fused. Last pedigerous somite (Figs 15 D, F, 16 B, C) with nearly symmetrical postero-lateral wings, each wing armed with one postero-lateral spine. Urosome (Figs 15 D, F, 16 A – D) two-segmented. Genital-double somite (Figs 15 A, D, F, 16 B – D) asymmetrical, ~ twice as long as wide, longer than anal somite and caudal rami combined; left proximal margin slightly dilated, with ~ 2 / 3 of right proximal margin expanded; distal part narrower than proximal part. Genital area on ventral surface with opercular pad protecting gonopores, and with rectangular and semicircular expansion (Fig. 16 C). Anal somite ~ 1.2 × as long as caudal rami. Caudal rami (Figs 15 F, 16 B) symmetrical, ~ 2.1 × as long as wide, parallel, with hairy outer and inner margins, each ramus with six setae; dorsal setae jointed, longer than principal setae. Left antennule, antenna, mandible, maxillule, maxilla, maxilliped, and P 1 – P 4 similar to those of the male. P 5 (Figs 15 E, G, 16 E) symmetrical. Coxa roughly spherical, with a stout, triangular spine anteriolaterally. Basis (Fig. 16 E) with one short, smooth sensory seta on distolateral margin (Fig. 16 E). Exp (Figs 15 E, G, 16 E) three-segmented; Exp - 1 cylindrical, ~ 2 × as long as wide, with almost straight inner and outer margins. Exp - 2 sub-triangular, with a row of strong spinules along both margins; Exp - 3 fused into a small prominence on Exp - 2, armed with one short spine and one long seta apically. Enp (Fig. 16 E) one-segmented, ~ 0.8 × as long as Exp - 1, armed with two strong, unequal spiniform setae; outer seta longest, with a row of tiny spinules apically. Distribution and ecology. Currently, T. kampucheaensis sp. nov. has been found only in two temporary-water habitats: a temporary pond in Kampong Cham Province and a shallow canal in Kandal Province, Cambodia. Representatives of the new species were found in two sites from the 147 sampled locations in five provinces (Kampong Chnang, Kampong Cham, Kendal, Prey Veng, and Takeo) in Cambodia. This species is rare and currently endemic to Cambodia. The newly discovered species was observed alongside two diaptomid species, namely Allodiaptomus raoi Kiefer, 1936, and Mongolodiaptomus mekongensis Sanoamuang & Watiroyram, 2018. Etymology. The specific name kampucheaensis refers to the name Kampuchea, which is the native name for Cambodia in the Khmer language, where the type locality is located. The suffix - ensis originates from Latin and indicates the specific origin.