Quadrimaera chaelata, Senna, André R. & Serejo, Cristiana S., 2007

Senna, André R. & Serejo, Cristiana S., 2007, Two new species of Quadrimaera (Crustacea: Amphipoda: Melitidae) from Atol das Rocas, Brazil, Zootaxa 1593, pp. 55-67 : 57-60

Quadrimaera chaelata sp. nov.

( Figures 1–4 )

Type material. Holotype: MNRJ 19600, male, 5.5 mm, Atol das Rocas, Barretão, from washed algae. P. S. Young, P. C. Paiva & A. A. Aguiar coll., October 19, 2000.

Paratypes: MNRJ 19601, 2 specimens, Atol das Rocas, Barretinha, C. S. Serejo & M. C. Rayol coll., October 25, 2001; MNRJ 19602, 1 specimen, Atol das Rocas, Salão, P. S. Young, P. C. Paiva & A. A. Aguiar coll., October 13, 2000; MNRJ 19603, 3 specimens, Atol das Rocas, Barretão, P. S. Young, P. C. Paiva & A. A. Aguiar coll., October 19, 2000.

Diagnosis. Gnathopod 2 chelate, palm obtuse, with a large medial concavity and several bifid stout setae; palmar corner produced into a stout process that slightly surpasses dactylus articulation.

Description. Holotype, male, 5.5 mm. Head without rostrum, eyes small. Antenna 1, ratio of articles of peduncle = 1.0:1.15:0.4, article 1 with only a few small distal setae, accessory flagellum 4-articulate. Antenna 2, first article of peduncle fused with the head. Lateral cephalic lobe truncate. Left mandible, incisor smooth; lacinia mobilis with four spines; setal row with five curved and acute stout setae; molar cylindrical and triturative with minute setae; palp 3-articulate, ratio of articles = 1.0:1.47:1.79, article 3 with three slender setae on inner margin and two long slender setae on apical margin. Maxilla 1, inner plate with two distal slender setae; outer plate with ten stout setae; palp 2-articulate with seven distal slender setae. Maxilla 2, inner plate with inner and distal margins setose; outer plate distally setose. Maxilliped, inner plate quadrate with a long slender seta on inner margin and three plumose slender setae distally; outer plate oval; palp 4-articulate, article 4 with three slender setae and one apical nail. Lower lip, inner margins setose with minute setae and one small stout seta. Upper lip with depressions and minute distal setae.

Coxae 1–2 subquadrate with four distal slender setae, coxa 1 anterodistally produced. Gnathopod 1, basis longer than ischium and merus combined; ischium with two slender setae; merus distally setose; carpus with several setae on posterior margin and lateral surface; propodus oval, slightly longer than carpus, palm oblique and setose, shorter than posterior margin; dactylus naked. Gnathopod 2 much longer and more robust than gnathopod 1, basis longer than ischium and merus combined with several little slender setae on anterior margin; carpus reduced, triangular; propodus robust, subrectangular, longer than broad, distally broadened; palm obtuse with a large medial concavity and several bifid stout setae; palmar corner produced into a stout process with a small distal concavity, process slightly surpassing dactylus articulation, making gnathopod 2 chelate; dactylus robust, with a slender seta on outer margin and two humps on inner margin. Pereopod 3 thin, basis slightly shorter than ischium, merus and carpus combined; propodus with several bifid setae on posterior margin; dactylus bearing two bifid slender setae. Pereopod 4 subequal to pereopod 3. Pereopod 5, basis narrow ovato-rectangular, posterior margin serrate with several slender setae, posterodistal lobe rounded; merus, anterior margin setose, with a distal tuft of setae, posterior margin setose, with a distal tuft of setae; carpus with two slender setae on anterior margin and tufts of setae on distal corners; propodus with anterior margin setose and tufts of setae on distal corners; dactylus with bifid nail. Pereopods 6–7 more robust than pereopod 5, merus with tufts of setae on anterior and posterior margins; carpus and propodus with tufts of setae on anterior margin; dactylus, anterior margin with a little hump and two small setae, lateral surface with a curved distal slender seta and a small bifid nail.

Epimeral plate 3 slightly produced posteriorly. Uropod 1, peduncle lengthened and thin, dorsally setose, with a ventroproximal seta and a lateral distal stout seta; rami dorsally and distally setose. Uropod 2, peduncle shorter than rami, with dorsal margins bearing two setae each; inner ramus longer than outer ramus; rami dorsally and distally setose, distally oblique. Uropod 3, peduncle naked and slightly longer than rami; inner ramus shorter than outer ramus; outer margin of outer ramus with long stout setae, rami distally truncate and setose. Telson nearly as long as broad, cleft at half its length, lobes distally notched with two unequal stout setae, outer margin with a distal slender seta.

Remarks. This species is included in Quadrimaera because it possesses all the diagnostic characters of the genus: mandibular palp article 1 not projected in an acute tooth, only one seta on outer margin of dactylus of gnathopod 2, palmar corner slightly shorter than 90°, and pereopods with bifid dactylus. Quadrimaera chaelata sp. nov. may be easily distinguished from other species of the genus by the the large medial concavity of the palm of the propodus on gnathopod 2, and by the stout distal process that makes gnathopod 2 chelate.

Distribution. Quadrimaera chaelata sp. nov. is endemic to Atol das Rocas.

Etymology. The name chaelata refers to the presence of a stout distal process on the palmar corner of gnathopod 2, making it chelate.

Figures

FIGURE 1. Quadrimaera chaelata sp. nov., holotype, male, MNRJ 19600. Scale for Hd represents 0.05 mm, remainder represent 0.1 mm.

FIGURE 2. Quadrimaera chaelata sp. nov., holotype, male, MNRJ 19600. Scales represent 0.1 mm.

FIGURE 3. Quadrimaera chaelata sp. nov., holotype, male, MNRJ 19600. Scales represent 0.1 mm.

FIGURE 4. Quadrimaera chaelata sp. nov., holotype, male, MNRJ 19600. Scales represent 0.05 mm.