A revision of the genus Orchestia Leach, 1814 with the reinstatement of O. inaequalipes (K. H. Barnard, 1951), the designation of a neotype for Orchestia gammarellus (Pallas 1776) and the description of three new species (Crustacea: Amphipoda: Talitridae Talitrinae) Author Myers, Alan A. School of Biological, Earth and Environmental Sciences, University College Cork, Cork Enterprise Centre, Distillery Fields, North Mall, Cork, Ireland. bavayia @ gmail. com; https: // orcid. org / 0000 - 0003 - 3256 - 2123 Author Lowry, James K. Australian Museum Research Institute, 1 William Street, Sydney, NSW 2010, Australia. text Zootaxa 2020 2020-07-02 4808 2 201 250 journal article 10.11646/zootaxa.4808.2.1 1175-5326 3933375 34BA963C-33B1-42BF-8340-D332B5C0628F Orchestia perezi sp. nov. ( Figs 29–31 ) Orchestia gammarellus .― Pérez-Schultheiss, 2014: 24 , figs 1–3. Types. Holotype , male, 12 mm (dissected), (MNHNCL AMP-15805). Playa Los Lilenes, Concón, Valparaiso Region , J. Perez-Schultheiss . Paratypes 1 female (dissected) (MNHNCL AMP-15806) same data as holotype . Other material studied. 11 males , 10 females , 12 juveniles ( CNMC 2020-0461 ), supratidal of La Herradura beach, Coquimbo , Chile , among shore vegetation, near small creek, hand collecting, 29°59’00.9”S 71°21’26.6”W ; Martin Thiel, 1 May 2019 . Type locality. Playa Los Lilenes , Concón Region de Valparaiso , Chile Etymology. Named after Dr Jorge Pérez-Schultheiss who first recognised the distinctness of this species. Description of adult male ( 17.4 mm male). Head. Eyes relatively large. Antenna 1 short, not reaching beyond peduncular article 4 of antenna 2. Antenna 2 peduncular article 5 subequal in length with peduncular article 4; flagellum subequal in length with combined length of peduncular articles 4 and 5, with 14 articles, final article cone shaped, with terminal cluster of imbricated setae. Labrum without epistome. Mandible left lacinia mobilis with 4 cusps. Maxilliped palp article 2 with distomedial lobe. FIGURE 29. Orchestia perezi sp. nov. , Coquimbo, Chile. FIGURE 30. Orchestia perezi sp. nov. , Male, Coquimbo, Chile; Female paratype, Los Lilenes, Valparaiso, Chile. Pereon. Gnathopod 1 subchelate, coxa smaller than that of coxa 2; posterior margin of carpus and propodus each with lobe covered in palmate setae; carpus moderately stout, with moderately developed palmate lobe; propodus length to carpus length 1:1.4; propodus strongly triangular; dactylus shorter than palm. Gnathopod 2 subchelate; basis 2.4 × as long as broad, merus posterior margin with 2 setae; propodus subovoid, distal width 1.5 × proximal width; dactylus stout, strongly convex. Pereopods 3–4 dactylus relatively slender, acute. Peropod 4 dactylus thickened proximally with a notch midway along posterior margin. Pereopod 5 basis subround, Pereopod 7 basis posterior margin distinctly serrate ; merus elongate, subrectangular (weakly triangular), 1.5 × (2 ×) as wide distally as proximally; carpus pyriform, 2–3 × as long as broad; subequal in length with merus; propodus elongate, 1.3 × length of carpus. Pleon. Epimeron 3 posterior margin weakly crenulate. Uropod 1 peduncle longer than rami, without distolateral robust seta; rami subequal. Uropod 2 peduncle longer than rami, rami subequal; exopod with 2 marginal robust setae; endopod with 2 marginal robust setae and 1 robust setae on inner face. U3 peduncle 1.8 × as long as broad, ramus slender 2.2 × as long as broad, 0.6 × length of peduncle , outer margin with 2 robust setae. Telson with 6 or less relatively slender apical robust setae on each side. Female. Gnathopod 2 basis 1.8 × as long as broad, anterior margin convex proximally, strongly concave distally , carpus 1.3 × length of propodus. Pereopod 7 basis subrectangular, flange on posterior margin strongly produced, posterior margin weakly serrate, merus and carpus unexpanded. Habitat. Supralittoral vegetation and near-shore wetland. Remarks. Orchestia perezi sp. nov. shares with the other southern hemisphere species O. inaequalipes (K.H. Barnard) and O. tabladoi sp. nov. , a telson that has only 6 or less relatively long and slender setae per lobe (more than 7 stouter setae in northern hemisphere species). Orchestia perezi sp. nov. differs from O. inaequalipes in the more weakly developed palmate lobes on the male gnathopod 1 carpus and propodus and in the proximally broad basis of the female gnathopod 2 (slender in O. inequalipes ). It differs from O. tabladoi sp. nov. in the shape of the carpus on the male pereopod 7 (pyriform and 2–3 × as long as broad in O. perezi sp. nov. but subround and almost as broad as long in O. tabladoi sp. nov. ) and in the shape of the female pereopod 7 basis, that is subrectangular with a very well developed but weakly serrate posterior margin in O. perezi sp. nov. , but subovoid with only a moderately developed but strongly serrate posterior margin in O. tabladoi sp. nov. FIGURE 31. Orchestia perezi sp. nov. , Coquimbo, Chile. Orchestia perezi differs from O. gammarellus (Pallas) in the form of the male pereopod 7. In O. perezi sp. nov. the posterior margin of the basis is strongly serrated, but in O. gammarellus it is scarcely serrate, the merus is weakly triangular in O. perezii sp. nov. , but strongly triangular in O. gammarellus . The basis of pereopod 5 is subround in O. perezi sp. nov. , but subovoid in O. gammarellus . The female pereopod 7 basis is more strongly subquadrangular in O. perezi sp. nov. than it is in O. gammarellus . Development of the secondary sexually enlarged pereopod 7 appears to occur only occasionally in adult males. Males can be found that are as large as males with strongly enlarged merus and carpus of pereopopod 7 yet have no significant development of the podomeres. Distributio n. Chile : La Herradura beach beach, Coquimbo ; Los Lilenes beach, Concón, Valparaiso region ( Pérez-Schultheiss 2014 , Myers & Lowry this paper) .