Myersius denticaudatus, Souza-Filho & Serejo, 2014

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, Zoological Journal of the Linnean Society 170 (1), pp. 34-85 : 60-63

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.

Figures

Figure 16. Myersius denticaudatus sp. nov. Holotype: male (2.5 mm), OCEANPROF II, BC-SUL, #59, 29 June 2003, 750 m, MNRJ 21424.

Figure 17. Myersius denticaudatus sp. nov. Holotype: male (2.5 mm), OCEANPROF II, BC-SUL, #59, 29 June 2003, 750 m, MNRJ 21424.

Figure 18. Myersius denticaudatus sp. nov. Paratype: female (3.2 mm), OCEANPROF I, BC-NORTE, #59, 12 December 2002, 750 m, MNRJ 21227.