Acroperus tupinamba, Sinev, Artem Y. & Elmoor-Loureiro, Lourdes M. A., 2010

Sinev, Artem Y. & Elmoor-Loureiro, Lourdes M. A., 2010, Three new species of chydorid cladocerans of subfamily Aloninae (Branchipoda: Anomopoda: Chydoridae) from Brazil, Zootaxa 2390, pp. 1-25 : 2-10

Acroperus tupinamba sp. nov.

( Figs. 1–3 )

Etymology. The name tupinamba refers to the largest tribe of indigenious people inhabiting Brazil before the European colonization.

Type location. Mestre D'Armas Stream, Planaltina, Distrito Federal, Brazil (15° 35' 42.3'' S, 47° 44' 45.2'' W). The type series was collected on 25.viii.2006 by F.D.R. Sousa, among decomposing leaves.

Holotype. An adult parthenogenetic female, MZUSP 19923. The label of holotype is: " Acroperus tupinamba sp. nov., 1 parth. Ƥ from Planaltina, DF, Brazil, HOLOTYPE ".

Paratypes. 1) five parthenogenetic females ( MZUSP 19924), five parthenogenetic females ( MNRJ 21587), five parthenogenetic females (EL01619), about 35 parthenogenetic females (EL1673), and 12 parthenogenetic females (AYS- 2008-09) from the type locality; 2) two parthenogenetic females from Santa Maria Reservoir (15° 40' 17 "S, 47° 57' 15" W) and three parthenogenetic females from Torto Reservoir (15° 41' 44 " S, 47° 54' 48" W), both located at Brasilia National Park, Distrito Federal, coll. by L.M.A. Elmoor- Loureiro, on 01.xi.1980 (slides EL01410 and EL01411); 4) four dissected parthenogenetic females from Cedro Pond, Brasília, Distrito Federal (15° 53' 50.2" S, 47° 56' 37.7" W), coll. by L.M.A. Elmoor-Loureiro, on 03.iv.2002 (slides EL01413 to EL01416); 5) a parthenogenetic female from Bonita Pond, Planaltina, Distrito Federal (15° 35' 22" S, 47° 41' 50" W), coll. by L.M.A. Elmoor-Loureiro, on 03.v.2005 (EL00765); 6) a parthenogenetic female from Emas National Park, Mineiros, Goiás (18° 16' 11" S, 52° 45' 18" W), coll. by V.M.G. Barros, on 21.iv.2000 (EL00767); 7) a parthenogenetic female from a pond at MT060 road, about 8 km South from Poconé, Mato Grosso (appr. 16° 21' 36" S, 56° 38' 48" W), coll. by L.M.A. Elmoor-Loureiro, on 06.ii.1986 (EL00769); 8) about 25 parthenogenetic females from a small fish pond at Laura Vicuña Center, Campo Grande, Mato Grosso do Sul (20° 31' S, 54° 39' W), coll. by L.M.A. Elmoor-Loureiro, on 06.viii.2000 (EL00718; AYS- 2008-12) a parthenogenetic female from a pond at Santana de Baixo Farm, Corumbataí, São Paulo (appr. 22° 17' 03" S, 47° 41' 04" W) coll. by L.M.A. Elmoor-Loureiro, on 24.viii.1996 (EL00770); 10) three parthenogenetic females from Vargem das Flores Reservoir, Contagem, Minas Gerais (appr. 19° 55' 08" S, 44° 10' 04" W), coll. by R.M. Pinto-Coelho, on 16.iv.1984 (EL00761); 11) a parthenogenetic female from Preto River, São Gonçalo do Rio Preto, Minas Gerais (18° 03' S, 43° 22' W) coll. by M.B.G. Souza, iii.1996 (slide EL01417); 12) a parthenogenetic female from a pond at BR020 road, about 3 km South from Roda Velha, Bahia (appr. 12° 47' 18" S, 45° 57' 06" W), coll. by L.M.A. Elmoor-Loureiro, on 30.vii.1985 (EL00761); 13) two parthenogenetic females from Mucugezinho River, Chapada Diamantina, Lençóis , Bahia (12° 27' S, 41° 24' W), coll. by V.M.G. Barros and M.Guimarães, on 01.ix.2004 (EL00762).

Diagnosis. Small Acroperus , length of female not exceeding 0.6 mm. Body oval or egg-shaped, moderately high, with maximum height in the second quarter of body. Dorsal margin from moderately to highly arched, posterior margin weakly to moderately concave. Denticles of posteroventral angle very small denticles, with broad bases. About 35–40 ventral setae, posterior setae longer than in other species of the genus. Valves with prominent sculpture in shape of diagonal lines, anterodorsal part of valves oblique. Head with low keel, distance between eye and margin of keel equal to eye diameter. Eye 1.5–2 times larger than ocellus. Head pores as for genus. Labrum as for genus.

Postabdomen slightly narrowing distally, shorter and wider than in other specimens of the genus, length about 3.2 height. Distal angle broadly rounded, not prominent. Dorsal margin straight in postanal portion and weakly concave in anal one. Preanal angle well defined, postanal angle weakly defined. Marginal denticles and lateral fascicles of setae as for genus. Setules near the base of postabdominal claws short, not exceeding the width of claw base. Postabdominal claw longer than anal portion of postabdomen. Basal spine long, about 0.3 length of claw itself. Spine at the end of pecten short, not exceeding width of claw here.

Antennule as for genus. Antenna less than 1/5 of body length. Antennal formula, setae 0-0-3/1-1-3, spines 1-0-1/0-0-1. Seta arising from basal segment of endopodite slightly shorter than middle segment. Seta arising from middle segment of endopodite 2.5 times longer than apical segment. All apical setae of same thickness and similar length. Apical spines about 2/3 length of apical segments. Limb I as for genus. Limb II as for genus, scrapers 6–7 of same thickness as others. Limb III as for genus. Limb IV as for genus, exopodite setae 5–6 with several long setules at the middle and with a peculiar structure at the end. Limb V as for genus, incursion between lobes of exopodite as a right angle. Limb VI as for genus.

Differential diagnosis. According to recent data ( Sinev 2009b), only two valid species of Acoperus are known, A. harpae (Baird, 1843) and A. angustatus Sars, 1863 . A. tupinamba sp. n. differs from both species by smaller size, long posterior setae of the valves, shorter and wider postabdomen, short setules near the base of postabdominal claw, long apical spines of antenna, peculiar morphology of exopodite IV setae 5–6, similar to that of Nicsmirnovius (see Van Damme et al. 2003). Other differences between species are summarized in Table 1 .

Description. Parthenogenetic female: Body with well-expressed dorsal keel, moderately high, oval or egg-shaped (height/length ratio from 0.65 to 0.72 in adult), with maximum height in the second quarter of body, strongly compressed laterally ( Fig. 1 A–D, 2A–D). Dorsal margin from moderately to highly arched, without depression between valves and head shield. Posterodorsal angle always rounded, posterior margin weakly to moderately concave. Posteroventral angles broadly rounded, provided with 1–3 very small denticles with broad bases, with small setules between ( Fig. 1 F–H). A row of about hundred short setules along posterior margin on inner side of carapace. Ventral margin from almost straight to irregularly convex. About 35–40 ventral setae ( Fig. 1 E), about 8 anteriormost setae long, next 15 setae short, posterior setae of intermediate length, longer than in other species of the genus. Anteroventral angle rounded. Valves with prominent sculpture in shape of diagonal, almost never anostomosing lines, in posteroventral portion of valves curved upward, anterodorsal part of valves oblique in some specimens.

Head with low keel, distance between eye and margin of keel varies equal to eye diameters. In lateral view, rostrum blunt, pointed downward. Eye 1.5–2 times larger than ocellus Three connected main head pores located on a widened area of head shield keel ( Fig. 2 E). PP = 0.4–0.8 IP. Lateral pores minute, located at the distance of 1.5–2 IP from midline, at level before anterior main pore. Labrum with narrow subtriangular keel, height about 2 width ( Fig. 1 I–J). Apex of keel rounded, dorsal margin without setules.

Postabdomen moderately long and narrow ( Fig. 1 K, 2F), in all specimens slightly narrowing distally, length about 3.2 height.Ventral margin almost straight. Basis of claws bordered from distal margin by clear incision. Distal margin straight, distal angle broadly rounded, but not prominent, as in other species. Dorsal margin straight in postanal portion and weakly concave in anal one, distal part about 2.5–3 times longer than preanal one, postanal portion slightly longer than anal one. Preanal angle well defined, postanal angle weakly defined. Postanal margin of postabdomen ( Fig. 2 H) provided with 8–9 groups of minute denticles, 2–5 denticles in each, anal margin—with 3–4 broad clusters of setules. 12–14 lateral fascicles of long setules, in distalmost fascicles length of setules exceed the width of base of postabdominal claw. A cluster of short setules located near the base of postabdominal claws.

Postabdominal claw ( Fig. 2 G) long, almost straight, longer than anal portion of postabdomen. Basal spine long, straight and thin, about 0.3 length of claw itself, bearing 5–7 setules. Spine at the end of pecten short, not exceeding width of claw here.

Antennule ( Fig. 2 I, 3A) long and narrow, with length about 4 widths, with 3 transverse rows of short setules at anterior face. Eight terminal aesthetascs, one of them 1.5 times longer and thicker than others, longer than antennula itself. Single lateral aesthetasc arise near the base of antennular seta, subequal to the largest terminal aesthetasc. Antennular seta thin, about 1/3 length of antennule, arising at 2/3 distance from the base.

Antenna ( Fig. 1 L, 2I) less than 1/5 of body length. Antennal formula, setae 0-0-3/1-1-3, spines 1-0-1/0-0- 1. Branches long and slender, of equal length. Seta arising from basal segment of endopodite slightly shorter than middle segment. Seta arising from middle segment of endopodite 2.5 times longer than apical segment. All apical setae of same thickness and similar length. Spine on basal segment of exopodite about 1\3 length of middle segment. Apical spines about 2/3 length of apical segments.

Thoracic limbs: six pairs.

Limb I ( Fig. 3 B–C) of moderate size. Epipodite rounded, with finger-like projection longer that epipodite itself. Accessory seta short. ODL with one long seta, with minute setules in distal part. IDL with three setae and several clusters of hard setules. IDL seta 1 large, well developed, both seta 2and 3 with strong setules in distal part, seta 3 slightly shorter than ODL seta, seta 2 about 2/3 length of seta 3. Endite 3 with four setae subequal in length. Endite 2 with two long distally setulated setae, both of them shorter than ODL seta, a shorter seta near their base, and a naked seta on anterior face of limb. Endite 1 with two 2-segmented setae and a long naked seta on anterior face of limb, 1.5 time longer than naked seta of endite 2. Six-seven rows of setules on ventral face of limb. Two ejector hooks of similar size.

Limb II sub triangular ( Fig. 3 D–E). Exopodite narrow, elongated, with very short. Inner portion of limb (“endopodite”) with eight scraping spines, increasing progressively in length distally. There is a soft seta near the base of scraper 1. Distal armature of gnathobase with four elements. Filter plate of seven setae, the posteriormost member considerably shorter, a cluster of long setules located near its base.

Limb III ( Fig. 3 F–H). Epipodite oval, without projection. Exopodite sub triangular, with seven setae, seta 3 being longest, seta 6 little shorter, seta 7 of about 2/3 length of seta 3, other setae short. Seta 3 armed with very long, hard setules in distal part and shorter setules in basal part, other setae with short setules. Distal endite with 3 setae decreasing in length basally ( Fig. 3 G). Two distalmost setae very slender, sharp, with about 5 long denticles, a small sensillum between their bases; basalmost setae flattened, setulated in distal part. Basal endite with 4 stiff, setulated distally setae, subequal in length. Gnathobase not clearly separated from basal endite. Four soft setae increasing in size basally, small sensillum near the base of distalmost seta. Distal armature of gnathobase with 3 elements. The first one an elongated, cylindrical sensillum, the second geniculated seta, the third - spines with splinted tip. Filter plate of seven setae.

Limb IV ( Fig. 3 I–L). Epipodite oval, with finger-like projection two times longer that epipodite itself. Exopodite of oval, with six setae, divided into lateral and distal group of three setae in each. Seta 3 being longest, seta 1–2 about 1/2 length of seta 3, seta 5–6 about 1/3 length of seta 3<seta 4 short. Setae 1–4 flattened, plumose, setae 1–2 with longer setules, setae 3–4 with shorter. Setae 5–6 slender, with several long setules at the middle and a peculiar structure at the end. Inner portion of limb IV with four setae and large round sensillum ( Fig. 3 L). Scraping seta short, with wide base and small denticles in distal part, flaming-torch setae with elongated basal part and short, slender distal part, each armed with 4–7 very long setules, longest of setules equal in length to setae bearing them. Three soft setae increasing in size basally. Gnathobase with a long 2-segmented, geniculated seta and a small hillock distally. Filter plate of five setae.

Limb V ( Fig. 3 M). Epipodite suboval, with finger-like projection 1.5 times longer that epipodite itself. Exopodite irregular, subdivided into two lobes, the incursion between lobes as right angle. Exopodite with four plumose setae, their length gradually decrease from seta 1 to seta 4. Seta 4 two times thicker than other setae. Inner limb portion as elongated narrow lobe, with short setules on the inner margin. At inner face, two setulated in distal part setae subequal in length, the distal one two times thicker than proximal. Filter plate of three short setae increasing in size distally, paired hillocks (sensillae?) between filter plate and inner face setae.

Limb VI ( Fig.3 N) as a trapezium-shaped lobe with setulated margin, very small in comparison with other limbs.

Size: In females of first juvenile instar, length 0.31–0.36 mm, height 0.20–0.23 mm, in females of second juvenile instar, length 0.39–0.43 mm, height 0.25–0.27 mm. In adult female, length 0.50–0.57 mm (up to 0.60 mm according to previous records ( Rey & Vasquez, 1986; Hudec, 1998), height 0.30–0.37 mm.

Distribution and ecology: Acroperus tupinamba has a wide distribution in Brazil, and has been found in marginal vegetated zone of ponds and reservoirs, as well in streams among marginal macrophytes or decomposing tree leaves.

Taxonomic notes. Recent revision ( Sinev 2009b) of Eurasian Acroperus revealed that the Palaearctic region is inhabited by two distinctive species, A. harpae and A. angustatus , instead of four, as presumed before ( Smirnov 1971). Taxonomic status of North American, African, and Australian populations of Acroperus is unclear, but their identity with Eurasian taxa is doubtful.

Populations of Acroperus from South America were usually identified as A. harpae ( Daday 1905; Thomasson 1953; Smirnov 1971; Montú & Gloeden, 1986; Ruiz & Bahamonde 1989; Rocha & Güntzel 1999; Santos-Wisniewski et al. 2002; Lima et al. 2003; Serafim Junior et al 2003; Holwedell et al. 2003; Eskinazi- Sant'Anna et al. 2005), A. cf. harpae ( Rey & Vasquez 1986) or Acroperus sp. ( Hudec 1998; Nogueira 2001). Expanded descriptions were published only twice for the populations from Venezuela ( Rey & Vasquez 1986; Hudec 1998), and in both cases the identity of studied populations with A. tupinamba is apparent. Both these populations have characteristic body shape, long posterior setae and small denticles of valves, weakly developed cluster of setules near base of postabdominal claw. Specimens described by Rey & Vasquez (1986) also have completely the same morphology of antenna. From modern point of view ( Frey 1987, 1995), presence of Paleoarctic Acroperus harpae in South America is quite improbable. Another South American species which was listed as member of Acroperus by Smirnov (1971) — Alonopsis titi Harding, 1955 , an endemic of Titicaca lake, lack head keel and reduced marginal setae of postabdomen characteristic for Acroperus s. str. and probably is a member of Alona s. lato.

An interesting feature of Acroperus tupinamba is a peculiar morphology of setae 5–6 of the limb IV exopodite, which is not present in other species of Acroperus ( Sinev 2009b) and rare for Aloninae in general. Setae of similar morphology are characteristical for the genera Nicsmirnovius (Van Damme et al. 2003) and Alonopsis ( Van Damme et al. 2009) . Several species of Phreatalona also have such morphology of exopodite IV seta 6, but the seta 5 is of common for the subfamily morphology ( Van Damme et al. 2009). Van Damme et al. (2003) suggested that such morphology of setae is an adaptation to the rheic conditions, but Acroperus tupinamba is encountered mostly in lakes and reservoirs, and both Alonopsis species are confined to lakes and bogs so we strongly doubt this hypothesis.

Figures

FIGURE 1. Acroperus tupinamba sp. n. from the type locality. A – B—juvenile females of instar I and II; C – Lparthenogenetic female: C – D—lateral view, E—ventral margin of valevs, F – H—posteroventral corner of valves, I – Jlabrum, K— postabdomen, L—antenna. Scale bars 0.1 mm for A – D, E, L, 0.05 mm for F – K.

FIGURE 2. Acroperus tupinamba sp. n. from the type locality, parthenogenetic females: A – B—lateral view, C—dorsolateral view, D—antero-lateral view, E—major head pres, F—postabdomen, G—postabdominal claw, H—lateral setules of postabdomen, I—antennula and antenna. Scale bars 0.1 mm for A – D, 0.01 mm for F – G, I, 0.002 mm for E, H.

FIGURE 3. Acroperus tupinamba sp. n. from the type locality, appendages of parthenogenetic female: A—antennule, B—limb I, C—ODL and IDL of limb I, D—limb II, E—exopodite of limb II, F—exopodite of limb III, G – H—inner portion of limb III, I—exopodite of limb IV, J—inner portion of limb IV (setules on flaming-torch setae not shown), Kflaming-torch setae of limn IV, L—sensilla of limb IV, M—limb V, N—limb VI. Scale bar 0.05 mm.

Tables

TABLE 1. Differences between valid species of Acroperus.

Character	Acroperus tupinamba sp.n	Acroperus harpae	Acroperus angustatus
Length of adult female	0.50–0.57 (0.6) mm	0.50–0.82 mm	0.55–0.95 mm
Posterior setae of valves	Long	short	Short
Denticles of valves	Saw-like, with broad base	With narrow base	Saw-like, with broad base
Postabdomen, length\height ratio	About 3.2	About 4	About 4
Distal angle of postabdomen	Not prominent	Prominent	Prominent
Setules near base of postabdoninal claw	Short, length less than width of claw base	Long, length about 1.5 widths of claw base	Long, length about 1.5 widths of claw base
Basal spine of postabdominal claw	Long, about 0.3 length of claw	Short, about 0.15 length of claw	Short, about 0.15 length of claw
Spine et the end of postabdominal claw pecten	Short, less that width of claw at the spot	Long, exceeding width of claw at the spot	Long, exceeding width of claw at the spot
Branches of antenna	Of same length	Endopodite longer than exopodite	Of same length
Seta on basal segment of antenna endopodite	Almost as long as middle segment	About 2/3 length of middle segment	As long as middle segment
Seta on middle segment of endopdite	Longer than endopodite	About half length of endopodite	Little shorter than endopodite
Apical setae of endopodite	Of same thickness	Of different thickness	Of same thickness
Apical spines of antenna	Long, about 2/3 length of middle segment	Short, less than half length of middle segment	Short, less than half length of middle segment
Scapers 6–7 of limb II	Similar to other scrapers	Similar to other scrapers	Broad, armed with robust denticles
Setae 5–6 of exopodite IV	With peculiar structures at the end	With narrow ends	With narrow ends
Incursion between lobes of exopodite V	Right angle	broad, trapezium-shaped	Sharp angle