Myersius denticaudatus Souza-Filho & Serejo 2014, SP. NOV.
Creators: name: Souza-Filho, Jesser F.
name: Serejo, Cristiana S.
Publisher: name: Zenodo
Year: 2014
Subjects: Biodiversity
Taxonomy
Animalia
Arthropoda
Malacostraca
Amphipoda
Ischyroceridae
Myersius
Myersius denticaudatus

description: MYERSIUS DENTICAUDATUS SP. NOV. (FIGS 16–18)    Etymology   
 The specific name denticaudatus is derived from the Latin ‘denti’ (= teeth) and ‘cauda’ (= tail, telson), and refers to the subdistal spines on the telson.   
 Material examined   
 Holotype: Male (2.5 mm), OCEANPROF II, BC-SUL, #59, Campos Basin, Rio de Janeiro, Brazil, 21°53′58.38″S, 39°55′32.22″W, 29 June 2003, 750 m, MNRJ 21424.   
 Paratype: One female (3.2 mm) (dissected and illustrated), OCEANPROF I, BC-NORTE, #59,   
Campos Basin, Rio de Janeiro, Brazil, 21°53′59.22″S, 39°55′30.36″W, 12 December 2002, 750 m, MNRJ 21227.  
 Type locality   
Campos Basin, Rio de Janeiro, Brazil.  
 Diagnosis   
Gnathopod 1 basis moderately stout, posterior margin convex, smooth; propodus palm acute, with two portions serrate, separated by a shallow dentate excavation, without palmar corner. Gnathopod 2 propodus ovate, massive; palm shorter than posterior margin, with one proximal triangular process followed by a large blunt process, palm corner defined by a short spine with three robust setae; dactylus slender, inner margin with three spines. Epimeron 3 rectangular. Uropod 1 peduncle interamal process 0.3 × peduncle length; outer margin with three marginal robust setae and one distal robust seta. Uropod 2 peduncle interamal process 0.16 × peduncle length. Uropod 3 outer ramus robust and shorter than inner ramus, with a subapical row of spines. Telson with three pairs of dorsomarginal pappose setae, one pair of dorsal slender setae, and two subapical spines.  
 Description   
Based on holotype male (2.5 mm), MNRJ 21424. Head longer than pereonites 1 and 2 together; anteroventral margin strongly recessed; lateral cephalic lobe acute; eyes absent. Antennae missing. Epistome acute and turned upwards. Mandible, palp article 3 spatulate, shorter than article 2, both with long pappose setae. Maxilla 1, inner plate with a single setae; outer plate with four bifid robust setae and six simple robust setae; palp 2-articulate and extended beyond outer plate, apex with four robust setae, and three slender facial setae. Maxilla 2 outer plate longer and wider than inner plate; both plates with marginal and submarginal pappose setae. Lower lip inner lobes well developed; mandibular process acute. Maxilliped, inner plate rectangular, with four distal robust setae and one subdistal seta; outer plate ovate, reaching about two-thirds the length of palp article 2, with three subdistal to distal robust setae, one slender seta, and one pappose robust seta; palp slender, 5-articulate; article 3 wider distally; articles 4 and 5 with a distal seta.  
Coxae 1–4 rectangular, slightly wider distally. Coxa 4 excavated posteriorly. Coxae 5–7 wider than long. Coxae 6 and 7 almost the same size, and shorter than coxa 5. Gnathopod 1 basis moderately stout, posterior margin convex, smooth; merus excavate; carpus slightly shorter than propodus, weakly lobate, posterior margin with many pappose setae; propodus palm acute, with two portions serrate separated by a shallow dentate excavation, without palmar corner; dactylus slender and long with medial serration. Gnathopod 2 basis moderately stout, posterior margin smooth, convex, inner margin slightly concave; merus longer than ischium; carpus triangulate, 0.54 × propodus length; propodus ovate, massive; palm shorter than posterior margin, with one proximal triangular process follow by a large blunt process, palm corner defined by a short spine with three robust setae; dactylus slender, inner margin with three spines. Pereopods 3 and 4 similar, basis moderately inflated; merus anterior margin expanded; propodus longer than carpus; dactylus slender and shorter than propodus.  
Epimeron 3 rectangular. Uropod 1 peduncle inner margin with two marginal robust setae and one distal robust seta; interamal process 0.3 × peduncle length; outer margin with three marginal robust setae and one distal robust seta. Uropod 2 peduncle shorter than inner ramus, with three marginal to apicolateral robust setae; interamal process 0.16 × peduncle length; inner ramus longer than outer ramus, with three marginal robust setae; outer ramus bearing two marginal robust setae. Uropod 3 peduncle with two marginal robust setae and two apical robust setae; outer ramus robust and shorter than inner ramus, with a subapical row of spines; inner ramus naked, with only one apical setule. Telson with three pairs of dorsomarginal pappose setae, one pair of dorsal slender setae, and two subapical spines.  
 Variations   
Paratype female (3.2 mm), MNRJ 21227. Antenna 1 setose, article 1 shorter than article 3; article 2 longer than article 3; accessory flagellum 2-articulate, article 1 longer than article 2.  
 Sexually dimorphic characters   
 Overall, the females of M. denticaudatus sp. nov. differ from males by: gnathopod 1 basis slender, posterior margin straight with two long setae; merus moderately excavate; carpus as long as propodus, posterior margin densely setose; propodus setose, palm serrate and acute, with one robust seta defining palmar corner; dactylus long, slender, inner margin serrate. Gnathopod 2 basis slender; carpus triangular and shorter than propodus, palm acute with one dentate triangular process near insertion of dactylus, followed by a large U-shaped excavation; palmar corner acute, with two pairs of facial robust setae.   
 Geographic distribution   
South-western Atlantic: Campos Basin, Rio de Janeiro, Brazil.
description: Published as part of Souza-Filho, Jesser F. & Serejo, Cristiana S., 2014, On the phylogeny of Ischyroceridae (Amphipoda, Senticaudata, Corophiida), with the description of a new genus and eight new species from deep-sea Brazilian waters, pp. 34-85 in Zoological Journal of the Linnean Society 170 (1) on pages 60-63, DOI: 10.1111/zoj.12099, http://zenodo.org/record/5301847