Platorchestia aquaticus, Suklom & Keetapithchayakul & Rahim & Wongkamhaeng, 2025

Suklom, Anotai, Keetapithchayakul, Tosaphol Saetung, Rahim, Azman Abdul & Wongkamhaeng, Koraon, 2025, Two new species of riparian hoppers (Amphipoda, Talitridae) from Trat and Samut Prakan provinces, Thailand, ZooKeys 1234, pp. 369-396 : 369-396

Platorchestia aquaticus sp. nov.

Figs 8 , 9 , 10 , 11 , 12

Type material.

Holotype • Thailand, 1 ♂; Bang Pu , Samut Prakan; 13°31.73'N, 100°38.17'E; 21 February 2021; Anotai Suklom; pit fall trap; THNHM-lv-20869 . Allotype • 1 ♀; collected with holotype; THNHM-lv-20870 . Paratypes • 2 ♂ and 2 ♀ collected with holotype; THNHM-lv-20871 .

Type locality.

On the shore of Klong Mai, Bang Pu, Samut Prakan, Thailand.

Habitat.

Riparian hoppers, living near urban areas in Bang Pu, Samut Prakan.

Ecological type.

Riparian hoppers (on the shore of canal under leaf litter or around the fibrous root of aquatic plants).

Diagnosis.

Male antenna 2 and pereopod 7 strongly sexually dimorphic. Male gnathopod 1 rudimentary cusp on dactylus. Male gnathopod 2 propodus without notch on palmar margin. Coxa 6 posterior lobe with anterodistal corner subquadrate, with process, one or two marginal setae, posterior margin perpendicular to ventral margin, outer surface with ridge. Pleopod 2 with two marginal robust setae; pleopod 3 with three marginal robust setae. Uropod 1 peduncle with nine or ten robust setae in two rows. Uropod 3 ramus with one marginal robust seta.

Description.

Based on holotype, male, 8.72 mm, THNHM-lv-20869 . Head. Eye medium ~ 1 / 3–1 / 5 of head length. Antenna 1 (Fig. 8 , A 1) short, slightly longer than article 4 of antenna 2. Antenna 2 (Fig. 8 , A 2) slightly incrassate, shorter than half body length; peduncular articles occasionally expanded, with small setae along the peduncle; article 4 shorter than article 5; flagellum with 15 articles, final article cone-shaped with apical cluster of setae. Upper lip (Fig. 9 , UL) broad, deep, apex round, without robust setae, apical margin with fine setules. Lower lip (Fig. 9 , LL) present; without inner plate, with fine setules on the apex and inner margins. Left mandible (Fig. 9 , LMD) incisor 5 - dentate; lacinia mobilis 5 - dentate, with six pappose setae type I in one row; molar strong and concave, with 22 striations, with cluster of fine setae on anterior side and one pappose setae type II on the dorsal side of molar. Right mandible (Fig. 9 , RMD) incisor 5 - dentate; lacinia mobilis with numerous cusps and four pappose setae type I in one row; molar strong and convex, with 22 striations, with cluster of fine setae on anterior side and one pappose seta type II on the dorsal side. Maxilla 1 (Fig. 9 , MX 1) inner plate slender with two apical papposerrate setae type I; outer plate with seven robust serrate setae type I; outer margin with small 2 - articulate palp. Maxilla 2 (Fig. 9 , MX 2) inner plate slightly shorter than outer plate; with 25 subapical setae, one papposerrate seta type I and 15 simple slender setae on inner margin; outer plate with 12 simple setae type I and one papposerrate seta type I, inner margin with four robust setae. Maxilliped (Fig. 9 , MP) inner plate with apical papposerrate setae type II and three large conical robust setae; outer plate with apical papposerrate setae; palp article two distomedial lobe well developed with numerous simple setae; article 4 present, reduced.

Pereon. Gnathopod 1 (Fig. 8 , G 1) sexually dimorphic; subchelate, coxa smaller than coxa 2, ventral margin with eight robust setae, anterior margin straight; basis expanded posteriorly, anterior margin with six robust setae, posterior margin with four robust setae; posterior margin of carpus and propodus each with lobe covered in palmate setae; ischium shortest; merus and carpus triangular; carpus 1.3 × longer than propodus; propodus subtriangular with well-developed posterior lobe, palm straight with four robust setae in one row; dactylus cuspidactylate, shorter than palm. Gnathopod 2 (Fig. 8 , G 2) sexually dimorphic; subchelate; coxa as wide as deep without posterior process, ventral margin convex with 13 robust setae; basis expanded, anterior margin straight with six robust setae, posterior margin slightly concave with six robust setae; ischium subrectangular, anterior margin without notch; merus subequal in length to carpus, convex on posterior margin; carpus triangular; reduce; enclosed by merus and propodus, posterior lobe absent; propodus subovate, palm acute and reaching 34.5–35 % along posterior margin, 1.5 × as long as wide, posteromedial surface of propodus with groove, anterior margin with one distal robust seta, palmar margin slightly convex with 14 robust setae; dactylus longer than palm and fitting in facial groove of propodus, attenuated distally. Pereopod 3 (Fig. 10 , P 3) coxa wider than deep without posterior process, ventral margin slightly convex and with 15 robust setae, anterior margin straight, anterior and posterior margins naked; basis slightly expanded distally, anterior margin straight with six robust setae, posterior margin slightly crenulate, with four groups of robust setae; ischium shortest, anterior margin with rounded process; merus slightly expanded, longer than carpus and propodus, anterior margin slightly rough and with seven robust setae, posterior margin slightly straight and with ten robust setae; carpus as long as propodus, anterior margin with three robust setae, posterior margin with five robust setae; propodus anterior margin with three groups of two robust setae in each group, posterior margin with three groups of three robust setae in each group, with two distal robust setae; dactylus posterior margin with one seta on anterior margin. Pereopod 4 (Fig. 10 , P 4) similar to pereopod 3 but shorter; coxa subrectangular, wider than deep, posterior margin with posterior process, ventral margin with 13 robust setae; basis slightly expanded distally, anterior margin with group of distal robust setae; ischium shortest, anterior margin convex, posterior margin straight with two robust setae; merus slightly expanded, longer than carpus and propodus, anterior margin crenulate with six robust setae, posterior margin crenulate with four groups of robust setae with two robust setae in each group; carpus as long as propodus, anterior margin straight with three robust setae, posterior margin slightly crenulate with seven robust setae; propodus slender, anterior margin with seven robust setae, posterior margin with three groups of robust setae; dactylus slender and longer than pereopod 3, thickened proximally with notch along posterior margin. Pereopod 5 (Fig. 10 , P 5) coxa bilobed, anterior lobe distinctly larger than posterior lobe, ventral margin with minute setae; basis ovate, anterior margin with seven robust setae, posterior margin with eight minute setae; ischium subrectangular, shortest, posterior margin notched; merus expanded distally, subequal in length to carpus, anterior margin slightly concave with seven robust setae, posterior margin convex with seven robust setae; carpus anterior margin crenulate with three groups of robust setae with three robust setae in each group, posterior margin slightly straight; propodus slender, longer than merus and carpus, anterior margin with four groups of robust setae with three robust setae in each group, posterior margin crenulate with five robust setae; dactylus with two robust setae on anterior margin. Pereopod 6 (Fig. 10 , P 6) coxa bilobed, anterior lobe very small, anterior margin straight, posterior lobe inner view posteroventral corner rounded, posterior margin perpendicular to ventral margin, ventral margin serrate and with minute setae; basis ovate, anterior margin with eight robust setae, posterior margin with six minute setae; ischium shortest; anterior margin straight, posterior margin with rounded process; merus slightly expanded, anterior margin crenulate, with nine robust setae, posterior margin convex and with six robust setae; carpus as long as merus, anterior margin crenulate and with four groups of robust setae, posterior margin crenulate with four groups of robust setae; propodus longer than merus and carpus, anterior margin slightly crenulate with 13 robust setae, posterior margin slightly crenulate with 16 robust setae; dactylus slender with subapical robust setae. Pereopod 7 (Fig. 10 , P 7) not sexually dimorphic, coxa reduced, ventral margin with minute setae; basis expanded without lateral sulcus, posterodistal lobe present, anterior margin with ten robust setae, posterior margin serrate with minute setae, ischium shortest with posterior process; merus as long as carpus, anterior margin slightly crenulate with ten robust setae, posterior margin with posteroventral lobe and five robust setae; carpus oblong; anterior margin slightly crenulate with eight robust setae, posterior margin crenulate with six robust setae; propodus slender, longer than merus and carpus, 1.17 × as long as carpus anterior margin with 13 robust setae, posterior margin with eight robust setae; dactylus slender, apically acute without robust setae.

Pleon. Pleopods 1–3 well developed, biramous; Pleopod 1 (Fig. 11 , PL 1) peduncle longer than rami, without marginal robust setae; inner ramus as long as outer ramus, with 15 articles; outer ramus with 14 articles. Pleopod 2 (Fig. 11 , PL 2) peduncle slightly longer than rami, with marginal robust setae on posterior margin; inner ramus as long as outer ramus, with 12 articles; outer ramus with 12 articles. Pleopod 3 (Fig. 11 , PL 3) peduncle longer than rami, posterodistal margin with 3 robust setae; inner ramus longer than outer ramus. with 11 articles; outer ramus with ten articles. Epimera 1–3 posterior margin slightly serrate, posteroventral corners of epimera 2 and 3 reduced. Uropod 1 (Fig. 11 , U 1) peduncle 1.5 × longer than rami, with seven robust setae in two rows, without distolateral robust setae; inner ramus subequal in length to outer ramus, with four marginal robust setae and three apical robust setae; outer ramus without marginal robust setae and with three apical robust setae. Uropod 2 (Fig. 11 , U 2) peduncle 1.3 × longer than rami, with four marginal robust setae; inner ramus with four marginal robust setae and 3 apical robust setae; outer ramus with one or two marginal robust setae and three apical robust setae. Uropod 3 (Fig. 11 , U 3) peduncle subequal in length to ramus, with three robust setae; ramus slender, more than 3.5 × longer than broad, with one marginal robust seta and four apical robust setae. Telson (Fig. 11 , T) longer than broad, apically incised, with three marginal robust setae and three apical robust setae per lobe; dorsal midline entire.

Male (minor form). Based on paratype, male 7.9 mm. THNHM-lv-20871 .

Head. Antenna 2 (Fig. 12 , A 2) peduncle not incrassate, peduncle slender.

Pereon. Gnathopod 1 (Fig. 12 , G 1); basis slightly expanded posteriorly, anterior margin with two robust setae, posterior margin with two robust setae; carpus 1.4 × longer than propodus; propodus anterior margin with two groups of robust setae; dactylus subequal to palm. Gnathopod 2 (Fig. 12 , G 2) coxa ventral margin with ten robust setae; basis anterior margin slightly concave with two robust setae, posterior margin expanded with four robust setae; ischium subrectangular, anterior margin with lobe; merus longer than carpus, convex on posterior margin; carpus triangular; reduced; enclosed by merus and propodus, posterior lobe absent; propodus subovate, palm acute reaching 45 % along posterior margin, 1.4 × as long as wide, palmar margin slightly convex with six robust setae; dactylus longer than palm and fitting in facial groove of propodus, attenuated distally.

Female (sexually dimorphic characters) based on allotype type, female 7.8 mm. THNHM-lv-20870 .

Pereon. Antenna 2 (Fig. 12 , A 2 ♀) peduncle slender. Gnathopod 1 (Fig. 12 , G 1 ♀) parachelate; posterior margin of merus, carpus and propodus without lobe covered in palmate setae; basis slightly expanded with posterodistal rounded process, anterior margin with six robust setae, posterior margin with three robust setae; ischium shortest, anterior margin with rounded lobe; merus triangular, posterior margin with six robust setae; carpus subtriangular, anterior margin straight with four robust setae, posterior margin convex with six robust setae in two groups, propodus subrectangular, palm acute, anterior margin with nine robust setae, posterior margin with 11 robust setae; dactylus much longer than palm, posterior margin with three robust setae. Gnathopod 2 (Fig. 12 , G 2 ♀) mitten-shaped, coxa posterior margin with acute process, ventral margin with minute setae; basis expanded, anterior margin convex with minute setae; ischium subrectangular, anterior margin with round lobe, posterior margin with four robust setae; merus, carpus, and propodus each with lobe covered in palmate setae; merus posterior lobe well developed with seven robust setae; carpus subtriangular; propodus subovate, palm obtuse, laterodistal corner with six robust setae in one line; dactylus slender, not longer than palm.

Distribution.

Thailand. Klong Mai, Bang Pu, Samut Prakan.

Etymology.

Named for the freshwater habitat where the species was collected.

Remarks.

Platorchestia aquaticus sp. nov. is the first species of Platorchestia recorded from Southeast Asia. The genus Platorchestia is classified as supra-littoral and terrestrial and is sexually dimorphic in antenna 2 and gnathopods 1 and 2. Males present two different forms in the population. The major form of P. aquaticus , based on the male holotype, appears similar to P. pacifica ( Miyamoto & Morino, 2004) , P. paraplatensis ( Serejo & Lowry, 2008) , and P. smithi ( Lowry, 2012) in the following characteristics: 1) mandible left lacinia mobilis 5 dentate, 2) coxae 3 and 4 as wide as deep, 3) gnathopod 1 dactylus slightly short or subequal to palm, 4) gnathopod 1 propodus subtriangular, palm transverse, 5) Uropod 3 peduncle with two or three robust setae, 6) telson longer than broad. However, Platorchestia aquaticus sp. nov. may be distinguished from other closely related species as follows: 1) gnathopod 1 with rudimentary cusps on dactylus ( P. pacifica and P. paraplatensis gnathopod 1 with distinct cusp on dactylus), 2) propodus of gnathopod 2 without notch on palmar margin, 3) uropod 1 peduncle with nine or ten robust setae in two rows, 4) uropod 3 ramus with single robust marginal seta, 5) telson with three robust marginal setae and three robust apical setae per lobe.

Figures

Figure 8. Platorchestia aquaticus sp. nov., holotype, male, 8.7 mm, THNHM-Iv- 20869. Scale bars: 0.2 mm.

Figure 9. Platorchestia aquaticus sp. nov., holotype, male, 8.7 mm, THNHM-Iv- 20869. Scale bars 0.2 mm.

Figure 10. Platorchestia aquaticus sp. nov., holotype, male, 8.7 mm, THNHM-Iv- 20869. Scale bars: 0.5 mm.

Figure 11. Platorchestia aquaticus sp. nov., holotype, male, 8.7 mm, THNHM-Iv- 20869. Scale bars: 0.5 mm (PL 1–3); 0.2 mm (U 1–2); 0.1 mm (U 3, T).

Figure 12. Platorchestia aquaticus sp. nov., paratype male 7.9 mm, THNHM-Iv- 20871, And allotype female 7.8 mm, THNHM-Iv- 20870. Scale bars: 0.5 mm (A 2, G 2); 0.2 mm (G 1).