Leptophoxoides marina, Senna, 2010

Senna, André R., 2010, A new genus and five new species of Phoxocephalidae (Crustacea: Amphipoda) from the south-east Brazilian deep sea, Journal of Natural History 44 (33 - 34), pp. 2075-2118 : 2093-2100

Leptophoxoides marina sp. nov.

( Figures 9–12 )

Material examined

Holotype: one male, 3.3 mm, Petrobras , Campos Basin, N / Rb Astro Garoupa, boxcorer, #59, 21°52′36″ S, 39°55′18″ W, 750 m depth, 12 December 2002, MNRJ 21042 . Paratypes: one female, 2.3 mm, Petrobras , Campos Basin, N/ Rb Astro Garoupa, box-corer, #46, 22°11′51″ S, 39°49′06″ W, 1350 m depth, 10 December 2002, MNRJ 21040 ; one female, 3.5 mm, Petrobras , Campos Basin, N/ Rb Astro Garoupa, box-corer, #73, 22°41′19″ S, 40°00′28″ W, 1950 m depth, 12 June 2003, MNRJ 21041 ; one female, 4.2 mm, Petrobras , Campos Basin, N/ Rb Astro Garoupa, box-corer, #59, 21°52′36″ S, 39°55′18″ W, 750 m depth, 12 December 2002, MNRJ 21043 ; one female, 2.3 mm, Petrobras , Campos Basin, N/ Rb Astro Garoupa, boxcorer, #70, 22°35′09″ S, 40°08′53″ W, 1050 m depth, 21 November 2002, MNRJ 21044 .

Etymology

The species name is a noun in apposition, and it is dedicated to my recently born baby daughter, Marina.

Diagnosis

Eyes absent. Antenna 1, article 2 of peduncle with one single ventroapical seta. Antenna 2, articles 3–4, ventral margin with long plumose setae. Maxilla 1, inner plate suboval, strongly shorter than outer plate. Gnathopod 1, coxa with four posteroventral long slender setae and one posterodorsal long slender seta. Pereopod 3, coxa with four posteroventral long slender setae. Pereopod 5, merus, carpus and propodus, anterior margin densely setose. Pereopod 6, basis about 1.5 times longer than broad, anterior margin with five distal rows of plumose setae (2-4-4-4-2), posterior expansion with three facial plumose setae; dactyl thin, elongated, as long as propodus. Uropod 3, peduncle short, about 1.5 times longer than broad, dorsoapical corner with three elongated setae, ventroapical corner with one seta; inner ramus small, about half length of the outer ramus article 1, with one small and apical slen- der seta; outer ramus article 1 about 1.6 times longer than peduncle, dorsal margin with three rows of setae (1-2-3); article 2 slender, spiniform, about half length article 1, with two apical slender setae. Telson elongated, about 1.4 times longer than broad, deeply cleft, about 85% of its length, apical margin with two long and one or two small setae, without lateral or dorsal setae.

Description

Head, rostrum well developed, constricted, sharp and deflexed; dorsal keel present; eyes absent. Antenna 1, article 1 without setae, about 0.75 times as long as broad, anteroventral corner truncate; article 2, short, about 0.4 times as long as broad, anteroventral corner bearing one elongated seta; article 3, short, about 0.6 times as long as broad, anteroventral corner with one slender seta; flagellum with five articulations; accessory flagellum with three articulations. Antenna 2, articles 3 and 4 ventral margin bearing long plumose setae; article 3, dorsoapical corner with one row of three stout setae; article 4 with one row of five facial stout setae, dorsoapical corner truncate, with one row of slender setae; article 5 short; flagellum short in female, with four articulations; elongated in male, slightly shorter than the body length. Mandible, incisor with three blunt spines; lacinia mobilis apically multicuspidate; accessory setal row with three main stout setae and three proximal setules; molar triturative; hump of palp small; palp with three articulations, article 1 small, about as long as broad, article 2, about three times longer than broad, inner margin with one proximal and one distal slender plumose seta, article 3, about three times longer than broad, subequal in length to article 2, apical margin truncate, with long slender setae. Maxilla 1, inner plate without setae, suboval, strongly shorter than outer plate; outer plate with seven apical multicuspidate stout setae; palp uni-articulated, with three apical elongated slender setae. Maxilla 2, weakly setose, inner plate wider and slightly shorter than outer plate. Maxilliped, inner plate small, slender, with setae only apically; outer plate small, slender, slightly longer than inner plate, inner margin poorly setose, apical margin with three small stout setae; palp with four articulations, articles 2 and 3, inner margin setose; article 3, about 1.8 times longer than article 2, apex strongly protuberant, blunt, with three apical elongated slender setae; dactyl elongated, outer margin with one proximal small slender seta, inner margin with one subapical small slender seta, apical nail distinct.

Gnathopod 1, coxa expanded anteriorly, anterior margin slightly concave, posterior margin with one posterodorsal long slender seta, ventral margin with four posteroventral long slender setae and one setule; basis, about 2.5 times longer than broad, posterior margin with two long slender setae, posteroventral corner with one long slender seta; merus, posterodistal corner produced, with one long slender seta; carpus with eusirid attachment; propodus subrectangular, anterior margin without setae, palm acute, slightly convex, setose, palmar corner defined by a small spine with one lateral stout seta; dactyl curved, reaching the palmar corner, outer margin with one proximal slender seta. Gnathopod 2, coxa subrectangular, about 1.5 times longer than broad, anterior margin straight, posterior margin without setae, ventral margin with three posteroventral long slender setae and one setule; basis, about three times longer than broad, posterior margin with three long slender setae, posteroventral corner with three long slender setae; merus, posterodistal corner produced, with two long slender setae; carpus with eusirid attachment; propodus subrectangular, anterior margin with small setae confined distally, palm acute, slightly convex, setose, palmar corner defined by a strong spine with one lateral long stout seta; dactyl curved, reaching the palmar corner, outer margin with one proximal slender seta. Pereopod 3, coxa subrectangular, about 1.5 times longer than broad, anterior margin almost straight, posterior margin without setae, ventral margin with four posteroventral long slender setae and one setule; basis, about 2.5 times longer than broad, anterior margin with one long slender seta, posterior margin with two long slender setae; merus, carpus and propodus, length ratio 22: 9: 11; merus, posterior margin with four rows of setae (1-2-2-3), anterodistal corner with one tuft of four setae; carpus, posterior margin densely setose; propodus, posteroventral corner with two elongated setae; dactyl as long as propodus. Pereopod 4, coxa slightly wider than long, anterior margin straight, posterior margin slightly oblique, ventral margin without posteroventral setae, posterodorsal margin strongly excavate; basis, about 2.5 times longer than broad, anterior margin with four long slender setae, posterior margin with two long slender setae, posteroventral corner with three long slender setae; merus, carpus, and propodus, length ratio 6: 2: 3; merus, posterior margin with four rows of setae (1-1-2-3), anterodistal corner with one tuft of six setae; carpus, posterior margin densely setose; propodus, posteroventral corner with three elongated setae; dactyl as long as propodus. Pereopod 5, basis posteriorly expanded, about as long as broad, posterior margin broadly rounded, smooth, without setae, posteroventral lobe weakly developed, anterior margin with two proximal long slender setae, anteroventral corner with two long slender setae; ischium, anteroventral corner with two long slender setae; merus, carpus and propodus, stout, length ratio 5: 5: 4; merus, anterior margin with three rows of setae (1-3-3), posteroventral corner with two long slender setae; carpus, anterior margin with three rows of setae (3-4-4), posteroventral corner with two long slender setae; propodus, anterior margin setose, posteroventral corner with two long slender setae; dactyl stout, about 0.7 times as long as propodus. Pereopod 6, coxa slightly expanded posteroventrally, posteroventral corner with one small setule; basis slightly expanded posteriorly, about 1.5 times longer than broad, anterior margin convex, with four proximal long slender setae and five distal rows of plumose setae (2-4-4-4-2), posterior expansion with one proximal long slender seta and three facial plumose setae; merus, carpus and propodus, length ratio 6: 5: 4; merus, anterior margin with two stout setae, anteroventral corner with two stout setae, posterior margin with one mid-length and one distal seta; carpus, anterior margin with three rows of setae (1-2-4), anteroventral corner with one slender and one long stout seta, posteroventral corner with two small slender, one long slender and one long stout seta, laterodistal margin with one small stout seta; propodus, anterior margin with three long slender setae continuously to apex, posteroventral corner with two small and one long slender seta; dactyl thin, elongated, as long as propodus. Pereopod 7, coxa slightly expanded posteroventrally; basis, strongly expanded posteriorly, anterior margin convex, with two proximal slender setae, posterior margin weakly serrate, weakly setulose, posteroventral lobe well developed, naked; merus, carpus and propodus, length ratio 3: 3: 2; merus, anterior margin with three rows of setae (1-3-5), posteroventral corner with one slender seta; carpus, anterior margin with three rows of setae (3-2-4); propodus, anteroventral corner with three long slender setae; dactyl thin, elongated, as long as propodus.

Epimeral plate 3, ventral and posterior margins without setae, posteroventral corner broadly rounded. Urosomite 3 smooth. Uropod 1, peduncle elongated, about 3.8 times longer than broad, laterodorsal margin with one proximal and one apical small stout seta, dorsoapical corner with one long seta, without inter-ramal spike; rami not continuously spinose to apex, subequal in length, slightly shorter than peduncle, subapical nail present; inner ramus, dorsal margin with one slender seta; outer ramus, dorsal margin with two slender setae. Uropod 2, peduncle slightly elongated, about three times longer than broad, laterodorsal margin with one slen- der seta, dorsoapical corner with one long seta; rami subequal in length, slightly longer than peduncle; inner ramus without setae; outer ramus with two lateral setae. Uropod 3, peduncle short, about 1.5 times longer than broad, dorsoapical corner with three long setae, ventroapical corner with one seta; inner ramus small, about half length outer ramus article 1, with one small apical slender seta; outer ramus article 1 about 1.6 times longer than peduncle, dorsal margin with three rows of setae (1-2-3), ventroapical corner with one long seta; article 2 slender, spiniform, about half length article 1, with two apical slender setae. Telson elongated, about 1.4 times longer than broad, deeply cleft, about 85% of its length, apical margin truncate, with two long and one or two short setae, lateral margin convex, without lateral or dorsal setae.

Remarks

Leptophoxoides marina sp. nov. is similar to L. molaris Barnard JL, 1962 from South Africa, in the diagnostic features of the genus, such as rostrum sharp and deflexed, mandible molar triturative, maxilla 1 palp uni-articulate, maxilliped palp article 3 apically protuberant, gnathopods 1 and 2 dissimilar, with palm acute, and epimeral plate 3 posteroventrally rounded. However, the new Brazilian species differs by the inner plate of maxilla 1 strongly shorter than outer plate, and inner ramus of uropod 3 about half length of the outer ramus article 1, features that bring the new species closer to Leptophoxus Sars, 1895 , the boreal sister genus of Leptophoxoides , with mandible molar not triturative. Moreover, Leptophoxoides marina sp. nov. has coxae 1 and 2 with four and three long posteroventral setae, respectively, versus two setae in both coxae 1 and 2 in L. molaris ; in L. marina sp. nov. pereopod 6 bears five distal rows of plumose setae on the anterior margin, and three facial plumose setae on its posterior expansion, in contrast to pereopod 6 anterior margin scarcely setose distally and posterior expansion without facial plumose setae in L. molaris . In the new taxon, the telson bears two long setae on the apical margin in each lobe, without lateral or dorsal setae, and it is about 1.4 times longer than broad, whereas in the South African species the telson bears one single long apical seta and one dorsolateral seta in each lobe, and it is about 2.5 times longer than broad.

Barnard and Drummond (1978) and Barnard and Karaman (1991) cite this genus as having eyes. Nevertheless, in the original description of L. molaris by Barnard JL (1962), the eyes are absent in drawings, and this feature is also omitted in the diagnosis of the genus and the species. Similarly, in L. marina sp. nov. the eyes are absent, but because I have not examined the type material of L. molaris , I cannot confidently assert that this is a difference. According to Thurston and Bett (1993), the positive correlation between eyelessness, depth and latitude is much stronger than the phylogenetic patterns of eye loss phenomena among gammaridean amphipods. Hence, the presence or absence of eyes is not a conclusive character with which to define genera.

Geographic distribution

Known only from the type locality, Campos Basin , off Rio de Janeiro State coast .

Bathymetric range

Collected from 750 m to 1950 m depth.

Figures

Figure 9. Leptophoxoides marina sp. nov.: male, 3.3 mm, holotype, Campos Basin, 21°52′36″ S, 39°55′18″ W, 750 m depth, 12 December 2002, MNRJ 21042; female, 2.3 mm, paratype, Campos Basin, 22°11′51″ S, 39°49′06″ W, 1350 m depth, 10 December 2002, MNRJ 21040. Scale bars: 0.1 mm for mHd; 1.0 mm for the remainder.

Figure 10. Leptophoxoides marina sp. nov.: male, 3.3 mm, holotype, Campos Basin, 21°52′36″ S, 39°55′18″ W, 750 m depth, 12 December 2002, MNRJ 21042; female, 2.3 mm, paratype, Campos Basin, 22°11′51″ S, 39°49′06″ W, 1350 m depth, 10 December 2002, MNRJ 21040. Scale bars: 0.1 mm.

Figure 11. Leptophoxoides marina sp. nov.: male, 3.3 mm, holotype, Campos Basin, 21°52′36″ S, 39°55′18″ W, 750 m depth, 12 December 2002, MNRJ 21042. Scale bars: 0.1 mm.

Figure 12. Leptophoxoides marina sp. nov.: male, 3.3 mm, holotype, Campos Basin, 21°52′36″ S, 39°55′18″ W, 750 m depth, 12 December 2002, MNRJ 21042. Scale bars: 0.1 mm.