Aruga emarginata, Sorrentino & Moraes & Senna, 2019

Sorrentino, Rayane, Moraes, Elienai E. B. & Senna, André R., 2019, Four new species of Lysianassidae Dana, 1849 (Crustacea: Amphipoda) From Northeastern Brazilian coast, Zootaxa 4585 (1), pp. 1-26 : 2-8

Aruga emarginata sp. nov.

( Figs 1–4 )

Material examined. Holotype, male, 8.4 mm, Pirangi Beach , Parnamirin , Rio Grande do Norte, Brazil (5°54'22''S 35°15'27''W). Reef of Parrachos do Pirangi , September and October /2009 UFBA 3222 .

Type-locality. Pirangi Beach, municipality of Parnamirim, Rio Grande do Norte, Brazil.

Etymology. The epithet refers to the apical margin of telson, strongly emarginated.

Diagnosis. Upper lip forming a tuned structure in distal margin. Margin posterior of epimeral plate 3 rounded; telson, lateral margins tapering and strongly emarginated.

Description. (Based on holotype) Head and body without setae. Head, deeper than long. Lateral cephalic lobe large; eyes reniform. Antenna 1, peduncle, article 1, 1.2 × as long than wide, dorsal margin slightly convex, ventral margin straight, with simple and plumose setae; article 2, 0.2 × peduncle article 1 length, dorsal margin with one slender seta, ventrodistal corner with plumose and simple setae; peduncle article 3, dorsal margin with three setae; primary flagellum 11-articulate, first article with two strong fields of callynophore; accessory flagellum 7- articulate, articles with slender setae on anterior margin. Antenna 2 elongate, almost reaches the length of body; peduncle, article 3, 0.4 × article 4 length; geniculate between peduncular articles 4 and 5, article 4, dorsal and ventral margins with small simple and plumose setae, ventral margin strongly convex; article 5 subrectangular, elongate, dorsal margin with sets of thin setae; flagellum 67-articulate, thirty-five proximal articles with setae in anterior margin, with robust calceoli.

Mouthpart bundle: subquadrate. Epistome and upper lip slightly separate, upper lip produced, slightly concave dorsally, apically acute, forming a tuned structure in distal margin, ventral margin densely setose. Mandible, incisor smooth and laminar; right mandible without lacinia mobilis, left mandible with lacinia mobilis modified in a slender seta, three robust accessory setae in both; molar rounded, triturative; palp 3-articulate, article 2, subrectangular, 2.2 × longer than article 1, anterior margin with slender setae; article 3, 0.6 × length of article 2, surface setose, anterior and apical margins with simple setae. Maxilla 1, outer plate, simple setae in lateral margin, setal-teeth in 6/5 arrangement: ST1–4 subconical, 2-cuspidate, ST5 3-cuspidate, ST6 5-cuspidate, ST7 3-cuspidate; STA, thin, 2-cuspidate, STB and C 2-cuspidate, STD simple; palp 2-articulate, article 2, 4.1 × longer than article 2, subrectangular, apical margin serrated, without subterminal seta. Maxilla 2, inner and outer plates narrow; inner plate, 3.5 × longer than wide, lateral margin with simple setae, one serrate seta in subapical margin, apical margin with slender setae; outer plate slightly longer than inner plate, apical margin rounded, with slender setae. Maxilliped, inner plate narrow, lateral margin with plumose and pectinate setae, apical margin with two simple setae, without nodular setae; outer plate, inner margin with one seta, serrate apically, outer margin convex; palp, 5- articulate, article 1 subquadrate, two setae in outer corner, article 2, rounded apically, article 3 longer, twice longer than wide, lateral margin with slender setae, article 4, lateral margins with slender setae, apical margin with setae, dactylus, slender and slightly curved, with subterminal small setae.

Gnathopod 1, simple, coxa large, anterior margin concave, anterodistal margin strongly produced and broadly round; basis, 1.8 × longer than wide, anterior margin with slender setae, posteroventral corner with one seta; ischium anterior margin concave proximally, convex in anteroventral corner, with one seta, posterior margin slightly convex, with setae; merus subtriangular, posterior margin setose; carpus trapezoidal, setae on anterodistal and posterodistal corners; propodus, approximately 1.6 × longer than carpus, slender setae in anterior and subterminal margins, posterior margin with setae; dactylus setose, slender and curved, with nail. Specimen is without gnathopod 2.

Pereopod 3, coxa, 1.9 × longer than wide; basis 2.7 × longer than wide, posterior and posteroventral margins with setae; ischium, posterior margin with slender setae; merus and carpus with plumose setae in posterior margin, merus, elongate, 2.1 × longer than wide, anterodistal margin expanded, carpus, 0.4 × merus length; propodus, subrectangular, 1.2 × longer than merus, six simple setae in posterior margin; dactylus elongate, 0.5 × propodus length, with nail. Pereopod 4, coxa deeper than wide, posterior margin expanded distally, forming a quadrate angle; basis, subrectangular, posterior margin with setae; ischium subquadrate, anterior margin a slightly convex projection, posterior margin with setae; merus and carpus, posterior margin with plumose setae; merus, 2 × longer than wide, expanded anteroventrally, with setae; carpus 0.5 × merus length, propodus, subrectangular, anteroventral and posterior margins with setae; dactylus elongate, 0.7 × length of propodus, with nail. Pereopod 5, coxa large, bilobate ventrally; basis strongly expanded posteriorly, anterior margin convex and setose, posteroventral lobe rounded; ischium small, about half length of merus, anteroventral corner with setae; merus, anterior and posterior margins with simple setae, rounded posteriorly; carpus and propodus subrectangular, anterior margin with setae, dactylus, with nail. Pereopod 6, coxa small, about half coxa 5 length; basis, anterior margin with setae distally, posterior margin slightly serrate, posteroventral lobe produced; ischium small, 0.8 × merus length, anterior margin with setae; merus, anterior and posterior margins with setae, slightly produced posteroventrally; carpus and propodus elongate, anterior and posteroventral margins with setae; dactylus with seta proximally, with nail. Pereopod 7, coxa reduced, anteroventral margin slightly straight and forming a convex angle in posteroventral margin; basis, anterior margin convex proximally, posterior margin convex; ischium, anteroventral margin with setae, ventral margin with a slightly convex projection; merus subrectangular, setae in anterior and posterior margin.

Epimeral plate 3, posteroventral corner rounded, posterior margin sinuous at its entire length and posteroventral corner rounded. Urosome 1–3 with three dorsal carinas, one in each lateral margin and one in medial margin. Urosomite 1, dorsal margin concave proximally, with row of setae in lateral carinas. Urosomite 2, short, 0.2 × urosomite 1 length. Urosomite 3 subquadrate, as long as deep with one seta in lateral carinas. Uropod 1, peduncle subequal in length to rami, 2.8 × longer than wide, dorsal margin with five setae and fine setae distally; rami subequal in length; inner ramus, dorsal margin with fine setae proximally and distally and two simple setae, with nail; outer ramus, with three setae ventrally, with nail. Uropod 2, peduncle, dorsal margin with three setae, medial margin with one seta; inner ramus, dorsal margin with fine setae and one simple seta, with a strongly constriction with a stout seta with accessory seta, with nail; outer ramus slightly longer than inner ramus, dorsal margin with three setae, with nail. Uropod 3, peduncle, dorsal margin with two setae, posterior margin with one seta, ventral margin with fine setae; inner ramus dorsal margin with plumose setae distally; outer ramus, 1.4 × longer than inner ramus, dorsal margin with long plumose setae distally, ventral margin with fine setae. Telson, entire, apically emarginated, with simple setae and plumose setae at apicolateral ends.

Remarks. Aruga emarginata sp. nov. differs from A. holmesi by the following characters (A. holmesi in parenthesis): epistome and upper lip separated by a thin and straight slit, upper lip, apical margin acute (welldefined separation, epistome has the anterior and ventral margins concave, upper lip rounded apically, ventral margin straight). Maxilla 1, outer plate, setal-teeth, ST1–4 subconical, 2-cuspidate (large, stout, ST1–3 weakly cuspidate to multicuspidate; ST4, 10-cuspidate), ST5 and ST7 3-cuspidate, ST6 4-cuspidate (ST5 and ST6 10- cuspidate, ST7 11-cuspidate), STD simple, without cusp (large, broad, 6-cuspidate). Maxilliped, inner plate subrectangular (subtriangular), without nodular setae (with 3 nodular setae); outer plate lateral margins straight, apical margin rounded medially (subovate). Urosome 1–3 with three dorsal carinas (without carinas). Telson strongly emarginated (slightly emarginated). Even though this is a male specimen, this species has the uropod 3, peduncle dorsal margin without plumose setae (A. holmesi that has superior margin with plumose setae).

Furthermore, in A. holmesi the basis of pereopod 4 is larger in size and the anterior margin and anteroventral corner is convex and the basis of pereopod 5 is subquadrate. The new species has pereopod 4, anterior margin almost straight, and pereopod 5, anteroventral and posteroventral corner strongly rounded. Pereopods 6 and 7 of A. holmesi have the posterior margins of basis more serrated than A. emarginata sp. nov., and the posterodistal margin of pereopod 7 in this species is slightly more convex than A. holmesi.

The species of North Pacific Ocean, Aruga oculata , is defined by having epimeral plate 3 with concave proximal half of posterior margin above a straight distal half, and the posteroventral corner unproduced and rounded, while the new species has the posterior margin sinuous along its entire length, and the posteroventral corner rounded.

This posterior margin of epimeral plate 3 is also different from Aruga kieppe sp. nov.. Besides that, A. emarginata sp. nov. fundamentally differs from A. kieppe sp. nov. by the presence of urosome 1 with dorsal laterals setose carinas, without keel and telson emarginate, with apical margin concave.

Aruga emarginata sp. nov differs from A. paracuru sp. nov. by having the upper lip slightly concave dorsally, apically acute, forming a tuned structure in distal margin, ventral margin densely setose. Mandible, molar rounded, triturative. Maxilla 1, setal-teeth STD simple; ST1 subconical, 2-cuspidate, ST7 3-cuspidate and STD simple. Maxilla 2, inner plate without pectinate setae. Telson with laterals slightly convex.

Regarding A. falklandica , this species differs from other species of Aruga by the presence of scattered setae on dorsal margin of pereon and pleon. Because of its simple description is not possible to make a considerable differentiation and comparison.

Figures

FIGURE 1. Aruga emarginata sp. nov.: male, holotype, Pirangi Beach, Parnamirim, 5°54'22''S 35°15'27''W; UFBA 3222. Scale bar: 1.0 mm.

FIGURE 2. Aruga emarginata sp. nov.: male, holotype, Pirangi Beach, Parnamirim, 5°54'22''S 35°15'27''W; UFBA 3222. Scale bars: 0.5 mm for E; 2.0 mm for A2; 1.0 mm for the remainder.

FIGURE 3. Aruga emarginata sp. nov.: male, holotype, Pirangi Beach, Parnamirim, 5°54'22''S 35°15'27''W; UFBA 3222. Scale bars: 1.0 mm for Md; 5 mm for the remainder.

FIGURE 4. Aruga emarginata sp. nov.: male, holotype, Pirangi Beach, Parnamirim, 5°54'22''S 35°15'27''W; UFBA 3222. Scale bars: 5.0 mm for P5–P7; 1.0 mm for U1–U3 and 0.5 mm for T.