Mexorchestia Wildish & LeCroy, 2014

Lowry, J. K. & Myers, A. A., 2022, Platorchestiinae subfam. nov. (Amphipoda, Senticaudata, Talitridae) with the description of three new genera and four new species, Zootaxa 5100 (1), pp. 1-53 : 27

Mexorchestia Wildish & LeCroy, 2014

Mexorchestia Wildish & LeCroy, 2014: 561 .

“ Tethorchestia ”.— LeCroy, 2011: 757.

Type species. Mexorchestia carpentaria carpentaria Wildish & LeCroy, 2014 , original designation.

Included species. Mexorchestia includes 1 species: M. carpenteri Wildish & LeCroy, 2014 .

Category. Mascupod.

Ecological type. Beach-hopper.

Habitat. Found on bare white sand and from wrack consisting of macroalgae and mangrove litter ( Wildish & LeCroy 2014).

Diagnostic description (male). Based on Wildish & LeCroy (2014).

Head. Antenna 2 peduncular articles slightly incrassate. Mandible left lacinia mobilis 5-cuspidate (tiny fifth cusp), or 4-cuspidate. Labium without inner lobes. Maxilliped palp article 2 with distomedial lobe; article 4 reduced, button-shaped.

Pereon. Gnathopod 1 sexually dimorphic; subchelate; posterior margin of carpus and propodus each with lobe covered in palmate setae; propodus anterior margin with 2 groups of robust setae, ‘subtriangular’ with welldeveloped posterodistal lobe, palm transverse; dactylus? simplidactylate. Gnathopod 2 subchelate; propodus palm acute, evenly rounded, without palmar sinuses; without large distal sinus; without proximal spine or thumb defining palm; dactylus attenuated distally. Pereopods 3–7 dactyli bicuspidactylate. Pereopod 4 dactylus amplidactylate, thickened proximally with notch midway along posterior margin. Pereopod 6 shorter than pereopod 7; not incrassate; basis expanded; male merus and carpus not expanded. Pereopod 7 not incrassate; basis broadly expanded; posterior margin smooth or minutely serrate margin with numerous small robust setae, posterodistal lobe absent; merus slightly expanded distally, subtriangular, anterior margin slightly convex; carpus unexpanded, subrectangular; propodus broad; length 6.7 × width, male with large distal tuft of setae. Oostegites (female) setae with spatulate tips.

Pleon. Pleopods all slightly reduced. Uropod 1 peduncle distolateral robust seta absent; exopod without marginal robust setae; endopod with marginal robust setae in 1 row. Uropod 2 exopod with marginal robust setae in 1 row; endopod with marginal robust setae in 2 rows. Uropod 3 ramus shorter than peduncle. Telson apically incised, with 7 to at least 10 robust setae per lobe.

Remarks. Wildish & LeCroy (2014) discuss the very close relationship between Mexorchestia and Tethorchestia . They distinguish the genera on the relative development of the distolateral robust seta on the peduncle of uropod 1, the shape of the female gnathopod 2 basis and the shape of the oostegites.

The slightly incrassate second antenna and large distal tuft of setae on the propodus of pereopod 7 and the distally attenuated dactylus of gnathopod 2 distinguish Mexorchestia and Tethorchestia from all other platorchestiine genera. There are several other characters separating these genera. Mexorchestia has a slightly incrassate antenna 2 (incrassate in Tethorchestia ); pereopod 6 merus expanded in Mexorchestia (not expanded in Tethorchestia ), pereopod 7 basis without a posterodistal lobe in Mexorchestia (present in Tethorchestia ) and oostegites with spatulate tips in Mexorchestia (simple in Tethorchestia ).

Distribution. USA: Florida. Caribbean Sea, Yucatan Peninsula to Belize ( Wildish & LeCroy 2014).