Spelaeogammarus titan, Senna, André R., Andrade, Luiz F., Castelo-Branco, Lucas P. & Ferreira, Rodrigo L., 2014

Senna, André R., Andrade, Luiz F., Castelo-Branco, Lucas P. & Ferreira, Rodrigo L., 2014, Spelaeogammarus titan, a new troglobitic amphipod from Brazil (Amphipoda: Bogidielloidea: Artesiidae), Zootaxa 3887 (1), pp. 55-67 : 56-66

publication ID	https://doi.org/ 10.11646/zootaxa.3887.1.3
publication LSID	lsid:zoobank.org:pub:F4BB8139-3A94-4E5E-8C0C-5974BB4E6C84
DOI	https://doi.org/10.5281/zenodo.5669140
persistent identifier	https://treatment.plazi.org/id/6F2987E5-FFF8-D547-2D9F-480A26B344BA
treatment provided by	Plazi
scientific name	Spelaeogammarus titan
status	sp. nov.

Treatment

Spelaeogammarus titan View in CoL sp. nov.

( Figs 2–7 View FIGURE 2 View FIGURE 3 View FIGURE 4 View FIGURE 5 View FIGURE 6 View FIGURE 7 )

Etymology. The specific epithet is related to the enlarged size of specimens of this species, greatly larger than the others in the genus.

Material examined. Holotype, female, dissected and drawn, 10.1 mm, 6 May 2013, cave PEA-445 (13º 05' 4.18''S; 44º 41' 58.88''W), municipality of Santa Maria da Vitória, Bahia state, Brazil, UFBA 1606. Paratypes: 1 female, habitus drawn, 18.3 mm, 6 May 2013, cave PEA-445 (13º 05' 4.18''S; 44º 41' 58.88''W), municipality of Santa Maria da Vitória, Bahia state, Brazil, UFBA 1607; 18 females, 6 May 2013, cave PEA-445 (13º 05' 4.18''S; 44º 41' 58.88''W), municipality of Santa Maria da Vitória, Bahia state, Brazil, UFBA 1608; 41 females, 6 May 2013, cave PEA-445 (13º 05' 4.18''S; 44º 41' 58.88''W), municipality of Santa Maria da Vitória, Bahia state, Brazil, ISLA 5142.

Diagnosis. Antenna 1, accessory flagellum 6-articulate. Antenna 2, flagellum 10-articulate. Maxilla 1, outer lobe, apical margin with 6 multi-cuspidate stout setae and 1 plumose seta. Maxilliped, inner plate, apical margin with 2 Y-shaped stout setae, 2 plumose setae, and 2 slender setae; palp article 3, apical margin bearing a row of small, blunt and plumose nodular setae. Gnathopod 1, basis, anterior margin with 7 small setae, posterior margin with 20 long setae; propodus stout, about 1.8X longer than basis. Gnathopod 2, basis, posterior margin with 23 setae. Coxa 5 with 1 stout setae and 14 slender setae, posterior lobe slightly concave. Coxa 6 with 1 stout seta. Pleopods, inner ramus with 10 to 13 setae. Uropod 3, outer ramus bearing 22 simple stout setae. Telson bearing 1 apical and 3 subapical stout setae in each lobe. Largest specimen: female, 18.3 mm.

Description. Body slender. Head without eyes, slightly deeper than long, about as long as pereonites 1 and 2 combined; rostrum weakly produced, subacute, lateral cephalic lobe rounded, anteroventral corner subquadrate, without setae. Antenna 1, about half the body length, peduncle slightly shorter than flagellum, article 1 0.7 X as long as articles 2 and 3 combined, ratio of peduncular articles 1–3 = 1.7:1.4:1; flagellum 26-articulate; accessory flagellum 6-articulate, article 6 reduced, total length of accessory flagellum as long as articles 1 to 6 of flagellum combined. Antenna 2, about 0.7 X the length of antenna 1, peduncle 2.7 X as long as flagellum, article 2 cone gland rising up to the distal margin of article 3, article 5 slightly shorter than article 4; flagellum 10-articulate.

Maxilla 1, inner plate subrectangular, bearing 3 stout plumose setae on apical margin, about 0.7 X as long as of outer plate; outer plate subrectangular, bearing 6 multi-cuspidate setae on apical margin, and 1 stout plumose seta at the innerdistal corner; palp 2-articulate, article 2 tapering distally, with a row of setae downwards from the apex to the inner margin. Maxilla 2, short, inner plate about 1.8 X wider than outer plate, apical margin bearing a fringe of plumose setae; outer plate slightly longer than inner plate, apical margin bearing a fringe of slender setae. Left mandible, molar broad, semi-triturative, subcircular, bearing a long slender plumose seta; accessory setal row consisting of 5 curved plumose setae, one of them longer and stronger than the others; lacinia mobilis present, well developed, broad and apically multi-cuspidate; incisor multi-cuspidate; palp 3-articulate, article 1 about twice longer than wide, article 2 slightly robust, about 3.9 X longer than wide, and about 1.3 X longer than article 3, ventral margin bearing 7 slender setae, article 3 tapering distally, with 2 apical long setae and 4 small slender setae on the ventral margin. Right mandible subequal to left mandible, accessory setal row consisting of 4 curved plumose setae, 2 of them longer and stronger than the others. Upper lip rounded and smooth, apically setulose. Lower lip, inner lobe apically rounded and setulose; outer lobe well developed, broadly rounded, inner distal margin setulose. Maxilliped, inner and outer plates short; inner plate suboval, apical margin with 2 Y-shaped stout setae, 2 plumose setae, and 2 slender setae; outer plate slightly elongate, suboval, bearing 6 stout setae on the inner distal margin; palp 4-articulate, article 1 about 1.4 X longer than wide, article 2, the largest, about 3 X longer than wide and 1.6 X longer than article 3, inner margin with a fringe of plumose setae, article 3 with distal submarginal field of setules, apical margin bearing a row of small, blunt and plumose nodular setae, inner margin with a fringe of plumose setae, article 4 tapering distally, inner margin concave and setose, a small claw present.

Gnathopod 1, coxa subquadrate; basis stout, about 1.8X longer than wide, anterior margin with 7 small setae, posterior margin bearing 20 long setae; isquium subquadrate, distoventral corner with 1 slender seta; merus, ventral margin setose; carpus subtriangular, posterodistal corner produced, with comb-scales, posterodistal margin with a fringe of plumose setae; propodus stout, suboval, sinuous, about 1.8X longer than basis, palm acute, about 2.7 X longer than posterior margin, covered by a dense fringe of small setae, bearing 13 stout setae; dactylus long, curved, naked, not reaching the palmar corner. Gnathopod 2, basis subrectangular, about 2.9 X longer than wide, posterior margin with 23 setae; isquium slightly longer than wide, posterior margin with 2 small slender setae; merus subrectangular, about 1.6 X longer than wide; carpus subtrapezoidal, about 1.5 longer than wide, posterior margin setose; propodus suboval, slightly elongate, about twice longer than wide, anterior and posterior margins setose, palm acute, about 0.75 X as long as posterior margin, covered by a dense fringe of small setae, bearing 8 stout setae, dactylus long, curved, naked, reaching beyond the palmar corner. Pereopod 3, coxa suboval, about 1.7 X longer than wide, ventral margin with 7 setae; basis suboval, slightly elongate, anterior and posterior margins without setae, posterodistal corner with 1 seta; merus, about 3.3 X longer than wide, slightly shorter than carpus, anterior margin with 2 stout setae, anterodistal corner with 2 stout setae, posterior margin with 8 setae; carpus elongate, about 5.5 X longer than wide, slightly longer than merus, anterior margin with 4 stout setae, posterior margin with 8 stout setae; propodus, slightly elongate, about 9 X longer than wide, slightly longer than carpus, anterior margin with 4 slender setae, posterior margin with 12 stout setae; dactylus slightly curved, apical nail present. Pereopod 4 subequal to pereopod 3, oostegite long and slender, naked or setae missing. Pereopod 5, coxa bilobate, anterior lobe well developed, about 1.6 X longer than wide, with 14 slender setae, posterior lobe small, posterior margin slightly concave, bearing 1 stout; basis suboval, about 2.3 X longer than wide, anterior and posterior margins bearing several marginal and submarginal stout and slender setae; merus about 3.8 X longer than wide, anterior margin with 8 slender setae and 1 proximal stout seta, posterior margin naked; carpus slightly elongate, 6.5 X longer than wide, about 1.2 X longer than merus, anterior margin with a dense fringe of slender setae, anterodistal corner with a set of long slender setae, posterior margin with 6 sparse slender setae; propodus slightly elongate, about 10 X longer than wide, about 0.9 X as long as carpus, bearing 13 lateral sets of stout setae (1-2-2-2-1-1-2-2-1-2-1-1-1), anterior margin with a dense fringe of small slender setae, anterodistal corner with 1 stout seta, posterior margin naked, posterodistal corner with 1 stout seta; dactylus slightly curved, apical nail present. Pereopod 6 slightly longer than pereopod 5, coxa bilobate, anterior lobe well developed, ventral margin naked, posterior margin with 1 stout seta; basis suboval, about twice longer than wide, anterior and posterior margins bearing several stout setae, merus slightly elongate, about 4.4 X longer than wide, anterior and posterior margins slightly setose; carpus slightly elongate, 6.9 X longer than wide, about 1.2 X longer than merus, anterior margin with a dense fringe of slender setae, distal setae longer than the proximal, anterodistal corner with 3 stout setae, posterior margin with 5 sparse slender setae, posterodistal corner with 1 stout seta; propodus slightly elongate, about 10.4 X longer than wide, about 0.9 X as long as carpus, bearing 14 lateral sets of stout setae (2-1-2- 1-2-2-1-2-2-1-1-2-1-2), anterior margin with a dense fringe of small slender setae, distal setae longer than the proximal, anterodistal corner with 1 stout seta, posterior margin naked; dactylus slightly curved, apical nail present. Pereopod 7 slightly longer than pereopod 6, coxa subtriangular, about 1.7 X wider than long, with 1 posterior stout seta; basis suboval, about 1.7 X longer than wide, anterior and posterior margins with several stout setae; ischium slightly stout; merus about 3.3 X longer than wide, anterior and posterior margins with 4 stout setae each, anterodistal corner with 2 stout setae, posterodistal corner with 4 stout setae; carpus slightly elongate, about 7.8 X longer than wide, about 1.4 X longer than merus, anterior margin with 8 sets of stout setae (3-2-3-3-3-1-3-3), anterodistal corner with 3 stout setae, posterior margin with 5 sparse stout setae, posterodistal corner with 2 stout setae; propodus elongate, about 13.2 X longer than wide, about 1.2 X longer than carpus, anterior and posterior margins densely setose; dactylus slightly curved, apical nail present.

Epimeral plates 1 and 2 subequal, posteroventral corner subquadrate, bearing a small spine, ventral and posterior margins naked. Epimeral plate 3, posteroventral corner subacute, weakly produced in a small spine, ventral and posterior margins naked. Pleopod 1, peduncle subrectangular, about 3.2 X longer than wide, naked; inner ramus 1-articulate, bearing 10 plumose slender setae; outer ramus 3-articulate, subequal in length to inner ramus, article 1, inner margin with 7 plumose setae, outer margin with 13 plumose setae, article 2 with 2 plumose setae, article 3, smallest, with 2 apical plumose setae. Pleopod 2, peduncle subrectangular, about 4.6 X longer than wide, naked; inner ramus 1-articulate, bearing 11 plumose slender setae; outer ramus 3-articulate, slightly longer than inner ramus, article 1, inner margin with 10 plumose setae, outer margin with 19 plumose setae, article 2 with 1 plumose seta, article 3, smallest, with 3 apical plumose setae. Pleopod 3, peduncle subrectangular, about 5.3 X longer than wide, naked; inner ramus 1-articulate, bearing 13 plumose slender setae; outer ramus 3-articulate, slightly longer than inner ramus, article 1, inner margin with 8 plumose setae, outer margin with 20 plumose setae, article 2 with 2 plumose seta, article 3, smallest, with 2 apical plumose setae. Uropod 1, peduncle short, about 1.6 X longer than wide, bearing 1 distolateral stout seta; rami subequal in length, lanceolate; inner ramus about 2.6 X longer than peduncle, bearing 9 dorsal, 1 ventrodistal, and 2 apical setae; outer ramus bearing 21 dorsal, 7 ventral, and 3 apical setae. Uropod 2, peduncle slightly elongate, about 2.4 X longer than wide, bearing 2 dorsal and 1 distolateral stout setae; rami subequal in length, slightly longer than peduncle; inner ramus bearing 2 dorsal, 1 ventrodistal, and 4 apical stout setae; outer ramus bearing 3 dorsal, 2 ventral, and 4 apical stout setae. Uropod 3, peduncle short, about 1.4 X longer than wide, bearing 2 dorsal and 1 distolateral stout setae; rami slightly elongate, Characters S. spinilacertus S.trajanoae S. santamensis S. bahiensis S . titan sp. nov.

Accessory flagellum 4-articulate 4-articulate 5-articulate 4-articulate 6-articulate lanceolate; inner ramus about 2.7 X longer than peduncle, bearing 11 dorsal, 1 ventrodistal, and 3 apical stout setae; outer ramus slightly longer than inner ramus, bearing 22 dorsal simple stout setae, 6 ventral pairs of bifid stout setae, and 3 apical stout setae. Telson slightly longer than wide, apical margin with shallow U-shaped excavation, bearing 1 apical and 3 subapical stout setae in each lobe.

Remarks. Spelaeogammarus titan sp. nov. is most closely related to S. santanensis than the others in the genus, by presenting antenna 2 flagellum 10-articulate, the maxilliped inner lobe with 2 plumose setae in the apical margin, the gnathopod 1 basis posterior margin with 20 setae and propodus much larger than basis (1.8X), the gnathopod 2 basis with 23 setae, the uropod 3 outer ramus with 8 bifid stout setae, and telson with 1 apical and 3 subapical setae in each lobe. However, the propodus of gnathopod 1 of S. titan sp. nov. is relatively larger than propodus in S. santanensis (1.5X), and the 8 bifid stout setae in the outer ramus of uropod 3 are placed in pairs with other 7 simple stout setae. Spelaeogammarus titan sp. nov. shares with other two species, S. spinilacertus and S. trajanoae , the maxilla 1 apical margin of outer lobe with 6 multi-cuspidate stout setae and 1 plumose seta. The new species presents as exclusive characteristics in the genus: the 6-articulate accessory flagellum, which modifies the diagnosis of the genus that was ranging from 4 to 5-articulate until now; the coxa 5 with posterior lobe slightly concave; the inner ramus of pleopods bears 10 to 13 plumose setae, while in all other species this number is much less, from 4 to 8; the dorsal margin of the outer ramus of uropod 3 with 22 simple stout setae, while the others species present 8 or 20 bifid setae; and the unique pattern of setation on the telson, bearing 1 apical and 3 subapical stout setae in each lobe.

Natural history and threats. The cave PEA-445 (13º 05' 4.18''S; 44º 41' 58.88''W) is located in Santa Maria da Vitória municipality, southeastern Bahia state, Brazil ( Fig 1 View FIGURE 1 A–B). The cave is inserted in sandstones from the Urucuia formation, and is placed in an altitude of 625 meters. The cave entrance is located at the bottom of a semicircular sinkhole, with around 10 meters of diameter. Such entrance is fragmented in two distinct irregular spans with around 2x 3 meters each. The entrance was certainly originated by a subsidence of the roof of the underground chamber. The cave is inserted in a silicified sandstone, densely fractured in a possible fault zone, in contrast to other caves in which other species of Speleogammarus are found, all inserted in limestones. However, it is important to stand out that under such sandstones may occur limestones from the Bambuí group, and the collapse of this subjacent limestone could have led to the collapse of the associated sandstones coverings, originating the cave. The cave comprises a chamber steeply sloping (slope -50%— Fig 1 View FIGURE 1 C) which follows the sinkhole slope, until intercepting a “lake” about 15 meters deep from the surface ( Fig 1 View FIGURE 1 D). The cave chamber has an irregular contour, with approximately 15 meters of linear development and 7.5 meters of depth (from the entrance until the lake). The "lake" in the bottom of the cave comprises the phreatic level of the area ( Fig 1 View FIGURE 1 D). In this "lake", root tufts from the external vegetation were observed in profusion. Amid the roots, hundreds of individuals of S. titan were observed ( Fig 1 View FIGURE 1 F), apparently feeding on decaying organic matter, brought down to the bottom of the cave by floods, or on exudates from the decomposing roots ( Fig 1 View FIGURE 1 E). The lake’s hydrochemistry was determined during one of the visits to the cave: turbidity 0; temperature 27o C; pH 7.77; electrical conductivity 195 µS/cm; total dissolved solids 97 mg /L; alkalinity 81.6 mg /L CaCO3.

Although the cave is located near a road and also near some residences, it apparently does not receive any visitors, due to the difficulty of access. Thus, its inner portion is quite preserved. However, it is worrying the advanced state of deforestation of the immediate epigean area surrounding the cave. The cave entrance is located in the middle portion of a narrow strip of vegetation (approximately 580 meters long by 37 meters wide) surrounded by areas of bare soil or with monocultures. Although one small border of this vegetated area is connected to an extensive preserved area, the cave is situated nearly 300 meters from this connection, being subject to changes resulting from external deforestation, which implies in alterations on the processes of input of organic resources from the external environments.