Mongolodiaptomus pectinidactylus ( Shen & Tai, 1964 )

Mongolodiaptomus pectinidactylus ( Shen & Tai, 1964) View in CoL

Figs 8 View Figure 8 , 9 View Figure 9

Sampling sites.

Samples were collected from four ponds in the Lao Pattana Village , Lao Pattana Sub-district, Na Wa District, Nakhon Phanom Province, north-eastern Thailand. The coordinates and elevations are as follows: 1) 17°35'4.59"N, 104°05'9.56"E, 151 m above sea level GoogleMaps ; 2) 17°35'0.15"N, 104°06'0.25"E, 152 m above sea level GoogleMaps ; 3) 17°34'6.05"N, 104°06'4.47"E, 147 m above sea level GoogleMaps ; 4) 17°35'6.71"N, 104°05'3.24"E, 155 m above sea level GoogleMaps .

Material examined.

Four adult males, each dissected and mounted on separate slide ( NPU 2025–05–08); three adult females prepared for scanning electron microscopy ( SEM) imaging. All specimens were collected on 4 August 2023 by Piyathida Monongdern.

Adult male. Urosomites 2–3 with hairs on ventral side. Caudal rami symmetrical, without chitinous prominence on right ramus ventrally. P 5 (Figs 8 A View Figure 8 , 9 A, B View Figure 9 ) asymmetrical, intercoxal plate with rounded distal margin. Right side of P 5: coxa with spiniform seta inserted on distal margin dorsally, not reaching mid-length of basis. Basis about twice as long as wide, with narrow hyaline lamella along proximal inner margin and hyaline prominence at middle of segment dorsally; row of tiny spinules on ventral surface (Fig. 8 B View Figure 8 ); small seta at 2 / 3 of segment length on ventral side. Exp three-segmented: Exp - 1 shorter than wide, with unproduced distal outer corner and semicircular hyaline prominence distally. Exp - 2 (Fig. 8 C, D View Figure 8 ) elongated, with broader middle part, about 2.5 times as long as wide; with blunt-tipped spine at 1 / 2 length of outer margin and blunt process distally; spine straight, shorter than half of segment length. Exp - 3 modified as sickle-shaped end claw with serrated inner about 1.5 times as long as Exp - 2. Enp one-segmented, conical, not reaching the mid-length of Exp - 2; with spinulated tip. Left side of P 5: coxa with thin seta at distal inner margin, reaching to mid-half of basis. Basis with narrow hyaline lamella along distal inner margin; with short, thin posterolateral seta on outer margin. Exp three-segmented: Exp - 1 longer than wide, gradually tapering in posterior end; with hair field at distal half of inner margin; Exp - 2 oval, smaller than Exp - 1; with inner robust seta, accompanied by spinular field along inner margin. Exp - 3 reduced to short, bare segment with rounded tip. Enp one-segmented, conical, gradually tapering distally; not reaching end of Exp - 1, with spinulate tip.

Adult female. Pediger 5 with almost symmetrical posterolateral wings; dorsal spine smaller than posterior spine on both wings. Genital double-somite asymmetrical; left side broadly expanded laterally at proximal part and with larger spine. Both spines on genital double-segment articulated, inserted on small somite prominence and directed down-laterally. Right margin concave, left margin convex. Anal somite and caudal rami as in male. P 5 (Fig. 8 E View Figure 8 ) symmetrical. Coxa with stout spine on prominence at distolateral corner in dorsal view; coxal spine reaching proximal margin of Exp - 1. Basis with thin seta on distolateral margin in dorsal view, reaching beyond middle of Exp - 1. Exp three-segmented and Enp two-segmented. Exp - 1 enlarged, rectangular, more than 2.0 times as long as wide. Exp - 2 (Fig. 8 F, G View Figure 8 ) subtriangular, symmetrical, both margins with row of strong spinules; two longitudinal ridges visible in ventral view; distal lateral seta modified into short, stout spine. Exp - 3 reduced to small spine, fused to base of Exp - 2 accompanied by one short and one long, thin seta. Enp subconical, extending beyond half-length of Exp - 1. Enp - 1 shorter than Enp - 2; Enp - 2 with circular row of spinules at narrowed apical end.

Variations.

The male right P 5 basis has one or two rows of tiny spinules amongst individuals in the population (Figs 8 B View Figure 8 , 9 B View Figure 9 ).

Distribution.

Mongolodiaptomus pectinidactylus has been sporadically recorded across China, Vietnam and Thailand ( Sanoamuang and Dabseepai 2021). In Thailand, it was previously reported from only two localities in the Roi Et and Ubon Ratchathani Provinces ( Sanoamuang 2002). More recently, additional records have been reported from the Sakon Nakhon and Nakhon Phanom Provinces ( Koompoot and Watiroyram 2025). The species has been found in both temporary and permanent waterbodies ( Sanoamuang and Dabseepai 2021), similar to the observations made in the present study.

Differential diagnosis.

Compared to the generic diagnoses by Kiefer (1938) and Ranga Reddy et al. (2000), the new species is assigned to the genus Mongolodiaptomus , based on the following characters: (1) urosomites 2–3 of the male with hairs on the ventral surface; (2) the presence of a spiniform seta on the male P 5 coxa; (3) the lateral spine on the right male P 5 Exp - 2 inserted at the 1 / 2 length of outer margin, accompanied by two accessory spines. The male P 5 intercoxal sclerite is rounded and unproduced, differing from the condition described by Kiefer (1938), but similar to that observed in M. calcarus , M. dumonti , M. gladiolus , M. mephistopheles and M. pectinidactylus . Additionally, the male lacks a chitinous prominence on the ventral side of the right caudal ramus, which also contrasts with Kiefer’s (1938) description.

The new species is distinguished from its congeners by the distinctive morphology of the right male P 5 Exp - 2 and the right caudal ramus, as well as by the absence of a chitinous prominence on the ventral side of the right caudal ramus. This combination of characters makes the new species most similar to M. pectinidactylus , a member of the M. mephistopheles ( Brehm, 1933) species group sensu Sanoamuang and Watiroyram (2018) and Sanoamuang and Koompoot (2024). Based on traditional taxonomy, particularly the morphology of pediger 5 in females, the urosome and the P 5 in both sexes, the species can be distinguished from M. pectinidactylus as follows: the female of the new species has an asymmetrical lateral wing on pediger 5, with the right dorsal spine and the left posterior spine being larger than those of M. pectinidactylus . Additionally, the female P 5 is asymmetrical, featuring a longer left Exp - 2 and a stouter right Exp - 2, whereas the P 5 is symmetrical in M. pectinidactylus . The seta on the female P 5 Exp - 2 is also distinctly shorter and stouter compared to that of M. pectinidactylus . The male of the new species lacks a row of spinules on the frontal surface of the P 5 basis, whereas this feature is present in M. pectinidactylus . In addition, the male P 5 Exp - 2 of the new species is slightly more distally expanded than that of M. pectinidactylus and the lateral spine is bent outwards, in contrast to the straight spine in M. pectinidactylus (Table 2 View Table 2 ).