Microcheus nortoni, Souza-Filho, 2011

Souza-Filho, Jesser F., 2011, First record of the family Cheidae (Amphipoda, Gammaridea) from the Brazilian coast, with description of two new genera and new species, Journal of Natural History 45 (5 - 6), pp. 327-346 : 330-336

Microcheus nortoni sp. nov.

( Figure 1–5 )

Etymology

The species is named in honour of Dr Norton M. Gianuca, from the Departamento de Oceanografia, Fundação Universidade Federal do Rio Grande, who collected the type material.

Material examined

Holotype, female 2.1 mm (dissected and mounted on three slides), Praia Jardim do Éden (30 ◦ 05 ′ S, 50 ◦ 10 ′ W), Rio Grande do Sul, intertidal, 11 April 2003, F. Monteiro col., MNRJ 21821 .

Paratypes: 6 females, Praia do Sol , Santa Catarina, 2005, intertidal, F. T . Tártari col., MNRJ 19543 ; 4 males, 4 females, 1 damaged, Praia do Cassino , Rio Grande do Sul, 27 November 1980, intertidal, N. M. Gianuca col., MNRJ 21818 ; 1 male, 1 female, Praia do Cassino , Rio Grande do Sul, 9 October 1974, intertidal, N. M. Gianuca col., MNRJ 21819 ; 16 males, 43 females, 2 ovigerous females, Praia Jardim do Éden (30 ◦ 05 ′ S, 50 ◦ 10 ′ W), Rio Grande do Sul, intertidal, 11 April 2003, F. Monteiro col., MNRJ 21820 ; 3 females (metal specimen stubs), Praia Jardim do Éden (30 ◦ 05 ′ S, 50 ◦ 10 ′ W), Rio Grande do Sul, intertidal, 11 April 2003, F. Monteiro col., MNRJ 21826 .

Description

Based on holotype female, 2.1 mm. Head subequal to pereonites 1–3 together; eyes poorly developed, composed of seven or eight ommatidia; rostrum long, ventral margin sinuous, cheek strongly developed, tip with a sensory organ. Antenna 1 and 2 inserted on ventral margin of head. Antenna 1 shorter than antenna 2; article 1 wider than long (2.5 ×), anterodistal corner with seven long setae and two pappose setae, posterodistal corner with two slender setae and two pappose setae; article 2 subequal to article 3, distal margin with six robust setae and two slender setae; primary flagellum with five articles, each one bearing an aesthetasc; accessory flagellum 0.8 × primary flagellum, with three articles. Antenna 2, article 1 with posterodistal corner rounded and produced, article 3 shorter than article 4 (0.4 ×), with one slender seta on anterodistal corner and three long setae on posterior margin; article 4 with six combs of robust setae being two facial (4-5), two subdistal (5-6) and two distal (5-2); article 5 subequal to article 4, anterior margin with one comb of two robust setae, posterior margin with three combs of robust setae (2-3-2), distal margin with five long setae and four pappose setae; flagellum with five articles.

Mandible with small molar, conical, non-triturative, setulose, with three robust setae apically; palp article 2 moderately inflated, with one margin seta; article 3 longer than article 2 (1.1 ×), with one long seta on facial margin, distal margin oblique bearing five long setae; left mandible incisor seven-dentate, lacinia mobilis large, fourdentate; setal row with four robust serrate setae and four plumose setae; right mandible incisor with five-dentate, lacinia mobilis small, triangular and simple; setal row with four robust serrate setae and three plumose setae. Lower lip with mandibular process well-developed. Maxilla 1 inner plate both inner and outer margins setulose and with two long distal setae; outer plate with six robust setae arranged in two lines (3-3) dissimilar in length, inner line composed of shortened robust setae; palp inner margin with five long setae. Maxilla 2 outer plate slightly longer than inner plate, with marginal and apical plumose setae; inner plate without a row of submarginal setae. Maxilliped inner plate reduced, reaching halfway along article 1 of palp, with three long setae; outer plate overreaching the end of article 1 of palp, with five marginal robust setae; palp long, article 2 inner margin lined with long and short setae, 1.4 × article 3 length, article 3 with distal margin setose, dactylus shorter than article 3.

Gnathopod 1 subchelate, eusirid-form, longer and more slender than gnathopod 2; coxa rectangular, posteroventral corner with two setae; basis elongate, slender (3.8 × as long as wide), widened distally, anterior margin with four long setae, posterior margin with two long setae; ischium subequal to merus; propodus 0.8 × length of basis, posterior margin with long setae, subdistal margin with an excavation to fit proximal part of propodus, distal margin truncate; propodus longer than wide (1.4 ×), anterodistal angle with four long setae, posterior margin sinuous, with two tufts of long setae; palm obtuse, convex and minutely serrate, palmar corner defined by a subacute process; dactylus long and slender, fitting the palm.

Gnathopod 2 more robust than gnathopod 1; coxa rectangular, posteroventral corner with four setae; basis elongate, slender (4.6X as long as wide), widened distally, anterior margin with two short and two long setae, posterior margin with three long setae; ischium subequal to merus; propodus robust, 0.5 × length of basis, posterior margin with seven long setae, subdistal margin with an excavation to fit proximal part of propodus, distal margin truncate; propodus longer than wide (1.25 ×), anterodistal angle with four long setae, posterior margin sinuous, with nine long setae; palm obtuse, convex and minutely serrate, palmar corner defined by a subacute process; dactylus long and slender, fitting the palm.

Pereopod 3 coxa subrectangular, posteroventral corner with five setae; basis moderately robust (2.6 × as long as wide), anterior margin with two long setae; ischium with a tuft of long setae on posterodistal corner; merus with anterodistal corner produced, twice as long as carpus; carpus robust, posterior margin with long setae, posterodistal corner with one long and robust setae; propodus slender (5 × as long as wide), posterior margin with 10 robust setae; dactylus robust, 0.5 × propodus length, bearing a subdistal spine.

Pereopod 4 coxa larger than coxae 1–3, widened distally, posterior margin excavated, anteroventral corner rounded, posteroventral corner produced; basis rectangular and slender (2.6 × as long as wide), posterodistal angle with three long setae; ischium with a tuft of long setae on posterodistal corner; merus with anterodistal corner produced, 1.5 × carpus length; carpus robust, posterior margin with eight long setae, posterodistal corner with one long and robust setae; propodus slender (4.2 × as long as wide), posterior margin with nine robust setae; dactylus robust, 0.5 × propodus length, bearing a subdistal spine.

Pereopod 5 coxa larger than coxae 6 and 7, wider than long (1.75 ×), bilobate, posterior lobe longer than anterior; basis ovate, anterior margin with three long setae, anteroventral corner with two setae, posterior margin rounded with posteroventral corner rounded and produced; ischium wider than long (1.6 ×); merus anterior margin with two combs of robust setae (2-5), posterior margin expanded with five long setae, posterodistal corner with four robust setae; carpus 1.4 × as long as wider, anterior margin with three combs of robust setae (5-7-5), posterior margin slightly expanded, with three combs of robust setae (3-3) and five long setae; propodus shorter than propodus, 2.2 × longer than wide, anterior margin with two combs of robust setae (3-4), anterodistal corner with three robust setae, posterior margin with two long setae, posterodistal corner with one robust seta and one long seta; dactylus robust 0.5 × propodus length, with a short subdistal spine on anterior margin.

Pereopod 6 coxa wider than long (1.5 ×), bilobate, posterior lobe longer than anterior; basis ovate, anterior margin with five tufts of long setae, posteroventral corner rounded and produced; ischium as long as wide; merus anterior margin with three combs of robust setae (1-1-4), posterior margin expanded with six long setae, posterodistal corner with six robust setae and three slender setae; carpus 1.4 × as long as wider, anterior margin with four combs of robust setae (2-4-5-6), posterior margin slightly expanded, with three combs of robust setae (2-2-3); propodus shorter than carpus, 2 × longer than wide, anterior margin with two combs of robust setae (4-4), posterior margin with two long setae, posterodistal corner with one robust seta; dactylus robust 0.4 × propodus length, with a short subdistal spine on anterior margin.

Pereopod 7 coxa wider than long (1.3 ×), posterior margin crenulate with four setae; basis ovate, anteroventral corner with a single short seta, posterior margin rounded, posteroventral corner rounded and produced; ischium longer than wide (1.25 ×); merus anterior margin with two combs of robust setae (2-4), posterior margin moderately expanded with two long setae, posterodistal corner with two robust setae and two long setae; carpus 1.45 × longer than wide, anterior margin with three combs of robust setae (4-4-5), posterior margin slightly expanded, with two combs of robust setae (1-2); propodus subequal to carpus, 3 × longer than wide, anterior margin with three combs of robust setae (3-3-4), posterior margin with one long seta, posterodistal corner with one robust seta and two long setae; dactylus robust 0.4 × propodus length, with a short subdistal spine on anterior margin.

Epimera 1 posterior margin convex, with eight slender setae. Epimera 2 posterior margin straight, with six slender setae, facial margin with six long plumose setae, ventrofacial margin with seven long plumose setae. Epimera 3 posterior margin almost straight with three slender setae.

Uropod 1 biramous, peduncle longer than outer ramus (1.45 ×), outer distal angle with a long and robust seta, inner margin with two long setae, basofacial margin with two long setae; outer ramus subequal to inner ramus, with two marginal long setae and two very long robust setae apically (subequal to ramus length); inner ramus with one marginal robust seta and three apical robust setae, the longest subequal to ramus length. Uropod 2 biramous, peduncle 1.3 × outer ramus, both outer and inner distal angle with a long seta; outer ramus with three slender setae; inner ramus shorter than outer ramus (0.6 ×), with one long seta apically. Uropod 3 peduncle shorter than inner ramus, inner margin with two robust setae, outer distal margin with seven robust setae; outer ramus 2-articulate, article 1 2.8 × article 2 length, outer margin with three combs of robust setae (3-3-3), inner margin with three plumose setae, article 2 truncate distally, with six distal setae; inner ramus lanceolate, shorter than article 1 of outer ramus (0.7 ×), inner margin with three plumose setae and one robust seta, distal margin with two plumose setae.

Telson wider than long (1.2 ×), deeply cleft, each lobe subacute distally, bearing one subdistal robust seta and one pappose seta, lateral margins with one pappose seta.

Male (sexually dimorphic characters only)

Only differs from female in having some aesthetascs on the flagellum of antenna 1.

Remarks

Microcheus nortoni gen. et sp. nov. is a relatively small species ranging from 1.5 to 2.3 mm length. Apart from the generic differences this species is easily distinguished from the others by the very long setae on antennae, pereopods and uropods.

Geographic distribution

Santa Catarina and Rio Grande do Sul, Brazil .

Figures

Figure 1. Microcheus nortoni gen. et sp. nov., holotype, female 2.1 mm, Praia Jardim do Éden, Tramandaí, Rio Grande do Sul, MNRJ 21821. Scale bars 0.1 mm.

Figure 2. Microcheus nortoni gen. et sp. nov., holotype, female 2.1 mm, Praia Jardim do Éden, Tramandaí, Rio Grande do Sul, MNRJ 21821. Scale bars 0.1 mm.

Figure 3. Microcheus nortoni gen. et sp. nov., holotype, female 2.1 mm, Praia Jardim do Éden, Tramandaí, Rio Grande do Sul, MNRJ 21821. Scale bar 0.1 mm.

Figure 4. Microcheus nortoni gen. et sp. nov., holotype, female 2.1 mm, Praia Jardim do Éden, Tramandaí, Rio Grande do Sul, MNRJ 21821. Scale bar 0.1 mm.

Figure 5. Microcheus nortoni gen. et sp. nov., paratype, female 2.2 mm, Praia Jardim do Éden, Tramandaí, Rio Grande do Sul, MNRJ 21826. Scale bars: Hb, Hd = 0.5 mm; M = 2 µm.