Thailandorchestia, 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

Genus Thailandorchestia gen. nov.

Type species.

Thailandorchestia rhizophila sp. nov., here designated.

Diagnosis.

Protorchestiidae with maxilliped palp article 2 distomedial lobe absent. Mandible left lacinia mobilis 4-dentate. Gnathopod 2 coxal gill simple. Pereopod 4 carpus significantly shorter than carpus of pereopod 3. Pereopods 6-7 sexually dimorphic (male merus and carpus incrassate). Pereopod 7 posterodistal lobe absent. Uropod 1 peduncle distolateral robust setae present, very large (1/3-1/2 length of outer ramus); inner ramus linear, not modified; outer ramus with marginal robust setae. Uropod 2 outer ramus without marginal robust setae. Uropod 3 peduncle with 2 robust setae; ramus shorter than peduncle, linear (narrowing). Telson apically incised, with 2 robust setae per lobe.

Etymology.

The generic name, Thailandorchestia gen. nov., is derived from “Thailand” in combination with the Orchestia stem.

Type locality.

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

Ecological type.

Driftwood hoppers (virtually confined to rotting driftwood where they live in galleries, consuming rotting driftwood and reproducing with relatively small broods).

Remarks.

The new genus clearly belongs to Protorchestiidae due to the presence of: 1) maxilliped palp article 2 without distomedial lobe; 2) article 4 small, distinct; 3) gnathopod 2 subchelate; 4) pereopods 3-7 simplidactylate; 5) pereopod 4 dactylus basidactylate; and 6) telson with apical robust setae only or with apical and marginal robust setae, with 1-6 robust setae per lobe.

The new genus is closely related to Microrchestia in having: 1) left mandible larcinia mobilis 4-dentate; 2) carpus of pereopod 3 subequal to those of pereopod 4; and 3) pereopods 6 and 7 sexually dimorphic. However, the current genus differs from Microrchestia from Australia by having: 1) maxilliped palp article 2 distomedial lobe absent (vs. well developed); 2) pereopod 7 posterodistal lobe absent (vs. present), and 3) U1 outer ramus with marginal robust setae (vs. without marginal robust setae) (Table 1 ).

Only one protochestiid amphipod had been previously reported from Thailand. Bussarawich (1985) studied the diversity of amphipods in the mangrove forest and reported Microchestia sp., a member of the family Protorchestiidae . Later, Lowry and Springthorpe (2015) revised the genus Cochinorchestia Lowry & Peart, 2010. Although the Microrchestia sp. from Thailand was also mentioned as a Cochinorchestia sp. based on the illustration of the previous publication, some details such as the maxilliped and gnathopods 1 and 2 remain unclear. The specimens from the report of Bussarawich (1985) presumed lost, which makes the Cochinorchestia sp. in this report still tentative.

The new genus is similar to Cochinorchestia from China in having: 1) left mandible larcinia mobilis 4-dentate; 2) carpus of pereopod 3 longer than that of pereopod 4; and 3) uropod 1 outer ramus with marginal setae. However, the current genus differs from Cochinorchestia in having: 1) pereopod 7 without a posterodistal lobe (vs. pereopod 7 with a posterodistal lobe); 2) uropod 1 outer ramus linear (vs. spoon-shaped) and uropod 3 peduncle with 2 robust setae (vs. with 3 robust setae); and 3) uropod 2 outer ramus without robust setae (vs. with marginal robust setae in 1 row).

The new genus is identifiable using the following key to genera of Protorchestiidae .