Tropodiaptomus kampucheaensis, Koompoot & Sanoamuang, 2025

Tropodiaptomus kampucheaensis sp. nov.

Figs 10 View Figure 10 , 11 View Figure 11 , 12 View Figure 12 , 13 View Figure 13 , 14 View Figure 14 , 15 View Figure 15 , 16 View Figure 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 View Figure 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 View Figure 10 , 12 A View Figure 12 ). Body smaller and slender than in female. Prosome ~ 2.5 × as long as urosome (Fig. 10 A View Figure 10 , 12 A View Figure 12 ). 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 View Figure 10 , 12 B View Figure 12 ).

Urosome (Figs 10 A – C View Figure 10 , 12 A – C View Figure 12 ) with five somites, unornamented. Genital somite dilated postero-laterally on both sides (Fig. 12 C View Figure 12 ), 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 View Figure 10 , 12 C View Figure 12 ). 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 View Figure 12 ). 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 View Figure 13 ): 25 - segmented. Armature formulae as in Table 4 View Table 4 . Right antennule geniculated (Figs 10 D View Figure 10 , 12 E – G View Figure 12 ), 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 View Figure 10 , 12 G View Figure 12 ). Armature formulae as in Table 5 View Table 5 .

Antenna (Fig. 13 B View Figure 13 ) 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 View Figure 13 ): 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 View Figure 13 ): 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 View Figure 13 ): 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 View Figure 13 ) 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 View Figure 14 ) 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 View Figure 14 ). 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 View Figure 14 ). Armature formulae of P 1 – P 4 as in Table 6 View Table 6 .

P 5 (Figs 11 A – F View Figure 11 , 12 D View Figure 12 ) highly asymmetrical. Intercoxal sclerite reduced, inner distal margin not produced. Coxae fused to intercoxal sclerite. Right P 5 (Figs 11 A – C, F View Figure 11 , 12 D View Figure 12 ): right coxa larger than left one, with a triangular spine on outer subdistal corner of posterior surface. Basis (Figs 11 A, B, F View Figure 11 , 12 D View Figure 12 ) rectangular, ~ 1.5 × as long as wide, ornamented with a thin, longitudinal hyaline membrane located at mid-length of inner margin (Figs 11 B View Figure 11 , 12 D View Figure 12 ), and a short seta at subdistal outer corner. Exp - 1 (Figs 11 A – C View Figure 11 , 12 D View Figure 12 ) shorter than wide, produce into acute process on outer distal corner. Exp - 2 (Figs 11 A, C View Figure 11 , 12 D View Figure 12 ) elongated, somewhat rectangular, ~ 1.9 × as long as wide, with a thin crescent-shaped lamella near base of principal lateral spine (Figs 11 C View Figure 11 , 12 D View Figure 12 ). 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 View Figure 11 , 12 D View Figure 12 ) 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 View Figure 11 , 12 D View Figure 12 ) 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 View Figure 11 ) 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 View Figure 11 ) 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 View Figure 15 ) symmetrical, with moderate strong and acutely pointed, paired filaments. Pdg 4 and Pdg 5 completely fused. Last pedigerous somite (Figs 15 D, F View Figure 15 , 16 B, C View Figure 16 ) with nearly symmetrical postero-lateral wings, each wing armed with one postero-lateral spine.

Urosome (Figs 15 D, F View Figure 15 , 16 A – D View Figure 16 ) two-segmented. Genital-double somite (Figs 15 A, D, F View Figure 15 , 16 B – D View Figure 16 ) 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 View Figure 16 ). Anal somite ~ 1.2 × as long as caudal rami. Caudal rami (Figs 15 F View Figure 15 , 16 B View Figure 16 ) 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 View Figure 15 , 16 E View Figure 16 ) symmetrical. Coxa roughly spherical, with a stout, triangular spine anteriolaterally. Basis (Fig. 16 E View Figure 16 ) with one short, smooth sensory seta on distolateral margin (Fig. 16 E View Figure 16 ). Exp (Figs 15 E, G View Figure 15 , 16 E View Figure 16 ) 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 View Figure 16 ) 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.