Mexorchestia: a new genus of talitrid amphipod (Crustacea, Amphipoda, Talitridae) from the Gulf of Mexico and Caribbean Sea, with the description of a new species and two new subspecies Author Wildish, David J. Author Lecroy, Sara E. text Zootaxa 2014 3856 4 555 577 journal article 10.11646/zootaxa.3856.4.5 67be3a9e-ed89-47eb-9bab-449b3cb12034 1175-5326 228560 E1CCD100-0EC7-49F7-9D52-0E7F15B58322 Mexorchestia carpenteri raduloviciae n. subsp. ( Figures 7 , 8 ) Material examined. Holotype : Male, 10.0 mm, near Black Bird Resort Center, Turneffe Island, Belize , 17°18′39″ N 87° 48′ 0 4′′ W , J. Hunt, 16 April 2010 , collected from wrack consisting of macroalgae and mangrove litter, USNM 1218150. Slide preparation USNM 1218150. Allotype: Female, 6.5 mm , same data as above, slide preparation USNM 1218151. Paratypes : 11 specimens , same data as above, collected 18 April 2010 , USNM 1218152. 19 specimens, Lighthouse Reef, Belize , 17° 17′ 30′′ N , 87° 31′ 10′′ W , J. Hunt, 20 April 2010 , on a white sand upper shore in seagrass wrack, USNM 1218153. 10 specimens, Lighthouse Reef, Belize , same position, 18 April 2010 , CMNC-2012-0021. Other samples were collected for mDNA studies from Cayo Norte (Chinchorro Bank), 18.747° N , 87.3038° W ; Mahahual, 18.712°N , 87.7102° W ; Punta Herrero, 18.324° N 87.4629° W and Xcalak, 18.272 °N 87.8346° W , all in Quintana Roo Province, Mexico ; A. Radulovici. The samples from Mexico are in the possession of A. Radulovici. Maximum body length (N = 29): males 11 mm , females 7 mm . Diagnosis. Small talitrids (< 11 mm ). Antenna 2, flagellum with 18–21 articles in adult males longer than 9 mm ; ovigerous female antenna 2 with 15–19 articles, oostegite 2 with 15–19 marginal setae; telson, each lobe with 2 distal dorsolateral robust setae; dorsal pigment pattern in both sexes diffuse on cephalon (may be absent); linear, club-shaped or absent on mid-line of pleon. Description. Based on male holotype , 10 mm . Cephalon ( Fig. 7 ): Cephalon and antennae similar to those of M. c. carpenteri n. subsp . Antenna 1, flagellum 5-articulate; antenna 2, flagellum 20-articulate. Mouthparts: Similar to those of M. c. carpenteri n. subsp . , with a 4 – 5 dentate lacinia mobilis in the left mandible. It was noted that the fifth tooth is very small and difficult to see in some specimens. Maxilla 1, inner plates with two terminal, plumose setae. Peraeon: Gnathopod 1 as in M. c. carpenteri n. subsp . , except dactyl slightly longer; thin robust setae at the base of posterior rounded lobes on carpus and propodus shorter. Pleon: Pleopods 1–3 as in M. c. carpenteri n. subsp . Urosome ( Fig. 7 ): Uropod 1, inner ramus with 4 marginal robust setae. Uropods 2–3 similar to those of M. c. carpenteri n. subsp . Telson, each lobe with 2 distal dorsolateral robust setae, otherwise similar to that of M. c. carpenteri n. subsp . Female. Based on 7 mm specimen from Turneffe Island, Belize . With similar dorsal pigment patterns as the male. Oostegite setal numbers (P2–P5) of: 15, 14, 11, 8. Sexual dimorphism as in M. c. carpenteri n. subsp . Etymology. The subspecific name is in honour of Dr. Adriana Radulovici, who first discovered this taxon in Mexico . The pronunciation is: rad ool ov ich ee ay. Epidermal pigment patterns. The freshly collected 10 mm male specimen preserved in dilute formalin was pale cream in background colour, with dorsal pigment markings deep red in colour. On transferring to isopropanol, the red pigment rapidly leached out. Just as in the nominate subspecies of the new genus, the DPP of M. c. raduloviciae n. subsp , was highly variable. The most pigmented morphs were from Turneffe Island ( Figs 8 A, B) with those from Lighthouse Reef showing DPP loss ( Fig 8 C, D) where the substrate was a white sand beach. The W shape of the epidermal pigments of the last peraeon segment ( Fig. 6 A–B) was lost in the more reduced DPP individuals ( Figs 8 C, D). Mid-line epidermal pigments of the pleon occur in only the most pigmented individuals ( Fig. 8 A, B) and not in others ( Fig 8 C, D). Note that the range of samples examined was limited (two populations from Belize ), and we were unable to investigate pigment patterns of the samples from Mexico , due to their preservation in ethanol which leaches out the epidermal pigments. Distribution. Caribbean Sea: Quintana Roo, Yucatan Peninsula, Mexico to Turneffe Island, Belize .