Thailandorchestia rhizophila, Wongkamhaeng & Dumrongrojwattana & Sumitrakij & Keetapithchayakul, 2022

Wongkamhaeng, Koraon, Dumrongrojwattana, Pongrat, Sumitrakij, Ratchaneewarn & Keetapithchayakul, Tosaphol Saetung, 2022, Thailandorchestia rhizophila sp. nov., a new genus and species of driftwood hopper (Crustacea, Amphipoda, Protorchestiidae) from Thailand, ZooKeys 1099, pp. 139-153 : 139

Thailandorchestia rhizophila sp. nov.

Diagnosis.

As for the genus unless otherwise stated. Antenna 1 long, reaching from midpoint to end of article 5 of antenna 2 peduncle. Eye medium (1/5-1/3 of head length). Gnathopod 1 not sexually dimorphic, palm transverse, dactylus shorter than palm. Gnathopod 2 sexually dimorphic (male subchelate, female mitten-shaped). Pleopod 1 outer ramus subequal in length to peduncle. Pleopod 3 outer ramus longer than peduncle.

Material examined.

Holotype, male, 8.04 mm, THNHM-Iv- 18760; allotype, female, 7.80 mm, THNHM-IV- 18961; Paratypes, 2 males, 1 non-gravid female, and 2 gravid females, THNHM- Iv 18761. All collected from the type locality on 4 May 2019, KW and PD leg.

Ecology.

Driftwood hoppers, living inside rotten logs and mangrove roots in the softest part under the bark. The mangrove forest is located near a small creek 50 meters from the beach. The sediment in the forest is muddy sand mixed with leaf litter.

Type locality.

Mangrove forest near Ban Ao Prao Beach (11°35'40.2"N, 102°33'52.6"E), Ko Kut District, Trat Province, Thailand.

Etymology.

The specific epithet refers to the habitat of this amphipod, which is also found inside mangrove roots.

Description of male holotype.

(THNHM-Iv- 18760, Figs 2 - 5 ).

Head. Eye medium (1/5-1/3 head length). Antenna 1 (Fig. 2A1 ) long, reaching from midpoint to end of article 5 of antenna 2 peduncle. Antenna 2 (Fig. 2A2 ) peduncular articles slender, article 5 longer than article 4. Upper lip (Fig. 3UL) without robust setae. Mandible (Fig. 3LMD) left lacinia mobilis 4-dentate. Maxilla 1 (Fig. 3MX1) with small palp, 1-articulate. Maxilliped (Fig. 3MP) palp article 2 distomedial lobe absent; article 4 small, well defined.

Pereon. Gnathopod 1 (Fig. 2G1 ) sexually dimorphic; subchelate; coxa 1 smaller than coxa 2; posterior margins of merus, carpus, and propodus each with lobe covered in palmate setae, palmate lobes present; propodus shorter than carpus, subrectangular; palm transverse. Gnathopod 2 (Fig. 2G2 ) sexually dimorphic; subchelate; coxal gill simple (or slightly lobate); basis slender; carpus triangular, reduced (enclosed by the merus and propodus), posterior lobe absent, not projecting between merus and propodus; 1.8 × as long as wide; palm acute, weakly toothed, with a subquadrate protuberance near dactylar ringe, lined with robust setae, posterodistal corner with socket; dactylus subequal in length to palm. Pereopod 3-4 (Fig. 4P3-P4 ) coxae wider than deep. Pereopods 3-7 (Fig. 4P3-P7 ) simplidactylate. Pereopod 4 (Fig. 4P4 ) subequal or slightly shorter than pereopod 3; carpus similar in length to pereopod 3 carpus; dactylus similar to pereopod 3 dactylus. Pereopod 5 propodus distinctly longer than carpus. Pereopod 6 (Fig. 4P6 ) slightly sexually dimorphic; shorter than pereopod 7; coxa posterior lobe inner view posteroventral corner rounded, posterior margin oblique with respect to ventral margin, posterior lobe without a ridge, posterior lobe without marginal setae; coxal gill lobate. Pereopod 7 (Fig. 4P7 ) sexually dimorphic (merus and carpus broadly incrassate); basis lateral sulcus absent, posterodistal lobe absent; distal articles (merus and carpus) expanded; merus posterior margin expanded distally, subtriangular.

Pleon. Pleopods all well developed. Pleopod 1 (Fig. 5PL1) peduncle without marginal setae; biramous, outer ramus subequal in length to peduncle; inner ramus with 17 articles, outer ramus with 13 articles. Pleopod 2 (Fig. 5PL2) peduncle without marginal setae; biramous, outer ramus subequal in length to peduncle; inner ramus with 15 articles, outer ramus with 14 articles. Pleopod 3 (Fig. 5PL3) peduncle without marginal setae; biramous, outer ramus subequal in length to peduncle; inner ramus with 15 articles, outer ramus with 13 articles. Uropod 1 (Fig. 5U1 ) peduncle with 4 robust setae, distolateral robust seta present, large (1/4 length of outer ramus), with simple tip; inner ramus subequal in length to outer ramus, inner ramus with marginal robust setae; outer ramus with 3 marginal robust setae. Uropod 2 (Fig. 5U2 ) inner ramus subequal in length to outer ramus, with marginal robust setae, with 3 lateral robust setae; outer ramus without marginal robust setae. Uropod 3 (Fig. 5U2 ) peduncle with 2 robust setae; ramus shorter than peduncle, ramus triangular, with 2 apical setae. Telson (Fig. 5T ) longer than broad, apically incised, dorsal midline vestigial or absent, with apical robust setae only and 2 robust setae per lobe.

Description of female allotype.

(THNHM-Iv- 18761, Figs 6 - 7 )

Pereon. Gnathopod 1 (Fig. 6G1 ) propodus narrower than that of male; dactylus subequal to palm. Gnathopod 2 (Fig. 6G2 ) mitten-shaped; basis slightly expanded; posterior margins of merus, carpus, and propodus each with lobe covered in palmate setae; carpus well developed (not enclosed by merus and propodus), posterior lobe present, projecting between merus and propodus; propodus length twice as long as wide; palm obtuse, smooth, without a protuberance or shelf near dactylar hinge, posterodistal corner naked; dactylus shorter than palm; gill lobate. Pereopod 5 (Fig. 7P5 ) propodus shorter than carpus. Distal articles (merus and carpus) slender. Preopods 6-7 (Fig. 7P6-7 ) sexually dimorphic (merus and carpus not broadly incrassate). Oostegites long (length greater than 2 × width), longer than wide, weakly setose, setae with simple, smooth tips.

Habitat.

Mangrove wood, inside roots and rotting logs.

Distribution.

Thailand, Ko Kut District, Inner Gulf of Thailand.

Figures

Figure 2. Thailandorchestia rhizophila sp. nov. holotype, male, 8.04 mm, THNHM-Iv- 18760. Scale bars: 1 mm.

Figure 4. Thailandorchestia rhizophila sp. nov. holotype, male, 8.04 mm, THNHM-Iv- 18760. Scale bars: 1 mm.

Figure 5. Thailandorchestia rhizophila sp. nov. holotype, male, 8.04 mm, THNHM-Iv- 18760. Scale bars (U 1 - U 3, T): 0.1 mm; (PL 1 - PL 3): 0.5 mm.

Figure 6. Thailandorchestia rhizophila sp. nov. allotype, female, 7.80 mm, THNHM-Iv- 18761. Scale bars: 1 mm.

Figure 7. Thailandorchestia rhizophila sp. nov. allotype, female, 7.80 mm, THNHM-Iv- 18761. Scale bars: 1 mm.