Bathybirubius margaretae, 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 : 2078-2085

Bathybirubius margaretae sp. nov.

( Figures 1–4 )

Material examined

Holotype: one female, 4.2 mm, Petrobras , Campos Basin, N / Rb Astro Garoupa, boxcorer, #50A, 22°02′31″ S, 39°52′14″ W, 1050 m depth, 29 June 2003, MNRJ 21416 . Paratype: one female, 2.8 mm, Petrobras , Campos Basin, N / Rb Astro Garoupa, boxcorer, #84, 22°26′17″ S, 39°58′32″ W, 1050 m depth, 20 June 2003, MNRJ 21027 .

Etymology

The species name is in honour of Dr Margaret M. Drummond, in recognition of her important contribution to phoxocephalid taxonomy through the extensive study of collections at Museum Victoria.

Diagnosis

Eyes round in female, unknown in male. Antenna 1, article 2 1.3 times longer than broad, ventral setae confined distally. Right mandible, lacinia mobilis bifid. Left lacinia mobilis apically multicuspidate. Coxa 4, anterior margin straight. Pereopod 6, basis 1.5 times longer than broad, anterior margin broadly convex, with six rows of setae (1-4-5-6-6-1); merus, carpus and propodus, length ratio 5: 6: 6. Pereopod 7, basis about 1.3 times longer than broad, posterior margin serrate. Epimeral plate 3, ventral margin naked, posterior margin with one small slender seta, posteroventral corner produced and broadly rounded. Uropod 3, peduncle, ventroapical corner with four long slender setae; inner ramus about half the length of outer ramus article 1, bearing one elongated slender seta apically; outer ramus, article 1 with two rows of two setae on outer margin, article 2 long, about half length of article 1.

Description

Head, rostrum weakly developed, unconstricted; eyes present. Antenna 1, peduncle article 1, about twice as long as broad, article 2 1.3 times longer than broad, long ventral setae confined distally; flagellum with seven articulations; accessory flagellum with five articulations. Antenna 2, article 4, with two rows of four facial slender setae, about 1.5 times longer than article 5, ventral margin densely setose; flagellum with six articulations. Right mandible, incisor with two spines; molar not triturative, conical, with two semi-articulated slender setae; lacinia mobilis bifid; accessory setal row with seven setae increasing in length distally; hump of palp small; palp with three articulations, article 1 twice as long as broad, article 2 slightly longer than article 3, inner margin with one mid-length and one distal slender seta, article 3 with two proximal facial slender setae, apical margin setose. Left mandible, incisor with two blunt spines; molar symmetrical; lacinia mobilis apically multicuspidate; accessory setal row with nine setae increasing in length distally.

Gnathopod 1, coxa expanded anteriorly, anterior margin convex, posterior margin straight, ventral margin with eight setae plus one setule; basis about three times longer than broad, anterior margin with one long seta distally, posterior margin with four long setae; merus subtriangular, posterior margin weakly setose; carpus without eusirid attachment; propodus ovato-rectangular, about twice as long as broad, anterior margin slightly convex, with two small slender setae placed distally, palm strongly acute, convex, minutely setose, palmar corner defined by a blunt projection with a lateral stout seta; dactyl curved, reaching the palmar corner, without setae. Gnathopod 2 similar to gnathopod 1, slightly enlarged; coxa weakly expanded anteriorly, posterior margin straight, ventral margin with eight setae; basis about three times longer than broad, more densely setose than in gnathopod 1; carpus without eusirid attachment; propodus ovato-rectangular, about twice as long as broad, anterior margin slightly convex, with one long slender seta distally, palm strongly acute, convex, minutely setose, palmar corner defined by a blunt projection with a lateral stout seta; dactyl curved, reaching the palmar corner, without setae. Pereopod 3, coxa rectangular, twice as long as broad, anterior and posterior margin subparallel, ventral margin with six setae; merus, carpus and propodus length ratio 4: 2: 3; merus, posterior margin with three rows of setae (3-3-5) and one row of three setae on the anterodistal corner; carpus, posterior margin densely setose; dactyl thin, 0.8 times as long as propodus. Pereopod 4, coxa posteriorly expanded, anterior margin straight, posterior margin slightly oblique, ventral margin with five setae plus one anterior and one posterior setule, posteroventral margin rounded, posterodorsal excavation present; merus, carpus and propodus, length ratio 6: 3: 4; merus, posterior margin with four rows of setae (1-3-4-5) and one row of three setae on the anterodistal corner; carpus, posteroventral margin densely setose; dactyl thin, 0.7 times as long as propodus. Pereopod 5, basis posteriorly expanded, subrectangular, not tapering distally, anterior margin continuously setose to apex, posterior margin with two minute setules, posteroventral lobe not developed; merus, carpus and propodus, length ratio 2: 2: 3; merus, anterior margin with four rows of setae (2-3-3-3), posterior margin with three rows of setae (1-2-3); carpus, anterior margin with three rows of setae (3-3-4), posterior margin with two rows (2-2); propodus, anterior margin with two rows (2-2) and one seta distally, posterior margin with two setae distally; dactyl thin, curved, 0.7 times as long as propodus. Pereopod 6, basis weakly expanded posteriorly, 1.5 times longer than broad, anterior margin broadly convex, with three proximal slender setae plus six rows of setae (1-4-5-6-6-1); merus, carpus and propodus, length ratio 5: 6: 6; merus, posterior margin with four rows of setae (1-1-2-3), anterodistal corner with two setae; propodus, anterior margin with three setae continuously to apex, posterior margin with three setae and one distal tuft of setae; dactyl thin, spiniform, half length of propodus. Pereopod 7, basis strongly expanded posteriorly, about 1.3 times longer than broad, anterior margin with two proximal slender setae, posterior margin serrate, posteroventral lobe rounded and smooth, merus, carpus and propodus, length ratio 8: 9: 11; merus, anterior margin with three rows of setae (2-2-2); carpus, anterior margin with two rows of setae (2-2), posteroventral corner with two long and one small slender setae; propodus, anterior margin with one row of three slender setae, posteroventral corner with one long slender seta; dactyl thin, 0.7 times as long as propodus.

Epimeral plate 3, ventral margin naked, posterior margin with one small slender seta, posteroventral corner produced and broadly rounded. Urosomite 3 smooth. Uropod 1, peduncle elongated, about four times longer than broad, dorsal margin weakly combed, with three distal stout setae, ventroapical corner with two stout setae; rami subequal in length to peduncle; inner ramus with two dorsal stout setae; outer ramus with three lateral stout setae. Uropod 2, peduncle elongated, about 3.5 times longer than broad, dorsal margin weakly combed, with four stout setae, ventroapical corner with one small stout seta; rami subequal in length, slightly longer than peduncle; inner ramus with one ventral stout seta; outer ramus with two lateral stout setae. Uropod 3, peduncle about 1.5 times longer than broad, dorsoapical corner with one tuft of four long slender setae, ventral margin with one distal small slender seta; inner ramus, about 2.8 times longer than broad, bearing one apical long slender seta; outer ramus, article 1 about twice as long as inner ramus, dorsal margin with two rows of two slender setae and one apical slender seta, ventral margin with one apical slender seta; article 2 slender, about 0.6 times as long as article 1, with two apical slender setae. Telson, almost completely cleft, about 1.2 times longer than broad, apical margin slightly truncate, with one blunt cusp, two apical stout setae and one curved slender seta on each lobe, without dorsal and lateral setae.

Remarks

Bathybirubius gen. nov. shares some characters with the Australian genus Birubius . Both genera have enlarged gnathopod 2, without eusirid attachment, pereopods 5 and 6, basis posteriorly expanded, posterior margin not setose, uropods 1 and 2 with dorsal margin of peduncles combed, epimeral plate 3 poorly setose, produced and telson almost completely cleft. However, the carpus of gnathopods 1 and 2 in Birubius is usually elongated. Only a few members of this genus, such as Birubius yorlunus Barnard and Drummond, 1978 , have this article shortened, about 1.5 times longer than broad, as in Bathybirubius gen. nov. Birubius has coxa 4 with diverse morphological patterns, anterior and posterior margins more or less divergent, ventral margin with or without long setae, posterodorsal corner rounded or sharp, but always the posterodorsal excavation is poorly developed. In Bathybirubius , the anterior and posterior margins are slightly divergent, the anterior margin being straight, the ventral margin having long setae. Nevertheless, the posterodorsal excavation is well developed in this genus. Merus, carpus and propodus of pereopods 5 and 6 in Bathybirubius are poorly enlarged and slender, in contrast to the greatly enlarged merus, carpus and propodus of pereopods 5 and 6 observed in Birubius . The peduncles of uropods 1 and 2 in both Bathybirubius and Birubius are combed, but in the new Brazilian genus, this ornamentation is much less well developed than in Birubius . Finally, epimeral plate 3 in Bathybirubius is broadly rounded, compared with epimeral plate 3 in Birubius , which is subquadrate and projected in a curved process upwards.

Bathybirubius margaretae sp. nov. resembles some Birubius species in different aspects. In Birubius lowannus Barnard and Drummond, 1978 and Birubius kyeemus Barnard and Drummond, 1978 the epimeral plate 3 is almost rounded, but with some small projections on the posterior margin. The latest species also has the inner ramus of uropod 3 about half length of the outer ramus article 1, as in B. margaretae sp. nov. Bathybirubius margaretae sp. nov. has long ventral setae on coxa 4 similar to some species of Birubius , such as: Birubius booleus Barnard and Drummond, 1978 ; Birubius eleebanus Barnard and Drummond, 1978 ; Birubius gelarus Barnard and Drummond, 1978 ; and Birubius panamunus Barnard and Drummond, 1976 . All Birubius species have merus and carpus of pereopod 6 more enlarged than in B. margaretae sp. nov., but some of those species, Birubius mayamayi Barnard and Drummond, 1978 , Birubius karobrani Barnard and Drummond, 1978 , Birubius booleus Barnard and Drummond, 1978 , Birubius babaneekus Barnard and Drummond, 1978 , Birubius gelarus Barnard and Drummond, 1978 and Birubius ularitus Barnard and Drummond, 1978 , have an unusual pereopod 6 with merus and carpus almost as slender as that seen in the Brazilian species.

Geographic distribution

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

Bathymetric range

Collected at 1050 m depth.

Figures

Figure 1. Bathybirubius margaretae gen. nov. sp. nov.: female, 4.2 mm, holotype, Campos Basin, 22°02′31″ S, 39°52′14″ W, 1050 m depth, 29 June 2003, MNRJ 21416. Scale bars: 1.0 mm for Hb; 0.1 mm for Hd.

Figure 2. Bathybirubius margaretae gen. nov. sp. nov.: female, 4.2 mm, holotype, Campos Basin, 22°02′31″ S, 39°52′14″ W, 1050 m depth, 29 June 2003, MNRJ 21416. Scale bars: 0.1 mm.

Figure 3. Bathybirubius margaretae gen. nov. sp. nov.: female, 4.2 mm, holotype, Campos Basin, 22°02′31″ S, 39°52′14″ W, 1050 m depth, 29 June 2003, MNRJ 21416. Scale bars: 0.1 mm.

Figure 4. Bathybirubius margaretae gen. nov. sp. nov.: female, 4.2 mm, holotype, Campos Basin, 22°02′31″ S, 39°52′14″ W, 1050 m depth, 29 June 2003, MNRJ 21416. Scale bars: 0.1 mm.