Anthalona neotropica

Description. Parthenogenetic female. Habitus (Figs 3 A – B, 5 A). Animal of medium size for the genus, length 0.30 – 0.37 mm; elongated, the carapace is oval in lateral view, maximum height near to anterior portion, about 1.6 times as long as high. Dorsal margin convex. Dorsal keel absent. Head (Figs 3 A – C, 5 C – D). Ocellus and eye of similar size. Headshield not studied. Rostrum short, rounded, projected towards ventral margin of carapace. Head pores as figured (Figs 3 E – I, 5 D). Two main pores of similar size connected; PP about 0.35 – 0.5 IP; underneath sacks of lateral head pores lobed (cosmaria). Labrum (Figs 3 J, 5 E). Morphology as in simplex - branch, keel without setules, notches or denticles; anterior margin convex. Maxilla I (Fig 4 A). Well developed, with two setulated setae. Antennule (Fig 3 N). Antennular body elongated, about 2.5 times longer than wide, three rows of short setules. Antennular sensory seta slender and short, about 0.4 times smaller than antennular body, inserted at 2 / 3 length from the base of antennule. Nine aesthetascs of different length; longer aesthetascs projecting beyond the tip of rostrum, none exceeds antennules length. Antenna II (Figs 3 O – P, 5 F). Coxal setae of equal length. Basipod thick, armed with one short spine. First segment of exopod with a cluster of long setulae exceeding the length of segment; second and third segments armed with relatively short and slender setulae in their terminal portion. First segment of endopod naked; second and third segments with short spinulae at the terminal portion; spine on first segment of endopod exceeding the middle-length of the second segment. Antennal formula: spines 001 / 101, setae 113 / 003. Setae on first segment of exopod not studied; seta on second segment of exopod bisegmented, long. Apical spines of endopod and exopod long, of similar size and longer than apical segments. Apical setae of exopod and endopod bisegmented and of similar size. Carapace (Figs 3 D, 5 B) covered by longitudinal lines at posterior region; ventral margin with a concavity in the middle; 31 – 37 not plumose setae per valve; short spines between marginal setae present; long setae in anterior group; long intermediate group contains relatively short setae; posterior group contains long setae. Posteroventral corner armed with spinulae not arranged in groups nor projected beyond the margin. Abdomen about 2.5 times shorter than thorax with at least two rows of abdominal setulae (Figs 3 A – C; L). Postabdomen (Figs 3 K – L, 5 H – I). Relatively short, about 2.5 times as long as wide; ventral margin slightly rounded, with two rows of spinulae. Pre-anal margin longer than anal and postanal margin. Anal margin concave, with evident angles, supplied with 3 – 4 groups of robust setulae. Postanal margin convex, armed with 5 – 6 lateral fascicles; first setule of each fascicle longer and thicker than the others; all fascicles exceeding postanal margin; also the margin bears 5 – 6 short marginal denticles. Postabdominal seta not studied. Postabdominal claw (Figs 3 K – M, 5 G). Implanted at the short projection from the postabdomen. Claw longer than anal margin of postabdomen, uniformly curved, with a group of at least two long spinules on the base; pecten divided in two groups; proximal group armed with longer spines compared to distal group. Basal spine length more than width of claw. Spine armed with spinulae along its dorsal margin. Limb I (Figs 4 B – D). Epipodite thin, oval, with a relatively long projection. ODL with a thin, distally serrulated seta, about the same length as IDL setae; accessory seta not studied. IDL (en 4) with a group of long spinulae on its face, two setae of similar length, bisegmented and armed with thin setulae. Third endite armed with short spinulae and four setae; two posterior setae densely setulated (a – b), the third posterior seta (c) and anterior seta 1 shorter. Second endite with three posterior setae (d – f), setae (f) and (e) armed with thick spinules on the lateral face; seta (d) armed with short setulae; seta (e) about 1.5 times longer than seta (f); seta (d) about 2.8 times shorter than seta (e). First endite with three marginal posterior setae (g – i), two bisegmented and setulated in distal part (g – h) and the third seta relatively shorter (i). No sensillae were found on the endites. Ejector hooks of different length armed with short denticles. Ventral face of limb armed with seven groups of setulae organized in clusters, decreasing towards the distal portion; distal clusters of short and strong setulae. Gnathobase elongated, apex as a projection with short setulae. Limb II (Figs 4 E – H). Exopodite elongated, with two rows of setulae; without seta. Inner limb portion with eight scrapers; scraper 6 – 8 markedly shorter than others and with bent apex; scraper 7 longer than 6 and 8; scrapers 1 – 4 armed with fine setulae; scrapers 5 – 8 armed with thin denticles. Proximal portion of the gnathobase short, wide and densely setulated; distal portion armed with four elements, first element as a small sensillum. Filter comb with seven setae; two posterior setae markedly shorter than other setae. Limb III (Figs 4 I – K). Epipodite oval, with a short projection. Exopodite relatively large, subquadrangular, with six marginal setae, subdivided into two groups: 2 lateral setae and 4 distal setae. Setae 1 – 2 of different length, both setulated. Third seta long, setulated, about 5.7 times longer than the sixth seta and 2.3 longer than fourth and fifth setae. Fourth and fifth setae of similar length, relatively long, setulated. Sixth seta short, about 2.4 times shorter than the fifth setae, naked. Distal endite (as initially proposed by Kotov 1999) with three anterior setae (1 – 3), two scraper-like similar in length (1 – 2); third seta slightly curved and armed with setulae bilaterally implanted (3); four plumose posterior setae increasing in length towards distal gnathobase (a – d). Basal endite with a sensillum and four soft setae (Fig. 4 J). Gnathobase armed with three elements, the first being a cylindrical sensillum, the second a geniculate seta, third element naked and with acute tip. Filter comb with seven setae (Fig. 4 K). Limb IV (Figs 4 L – N). Pre-epipodite round, densely setulated. Epipodite oval, with long projection. Exopodite round, with six marginal setae; lateral setae 1 – 4 plumose; seta 1 slightly longer than seta 2; third seta about same length of the first seta; fourth seta about 1.6 times longer than fifth seta; two distal setae (5 – 6) short, fifth seta naked, markedly longer than sixth seta; sixth seta naked. Distal endite with four anterior setae (1 – 4), one scraperlike (1) and three flaming-torch-like (2 – 4); first flaming-torch seta (2) robust, with long setulae. Basal endite with three posterior soft setae increasing in size towards the base. Gnathobase armed with a sensillum and a setulated seta implanted on a robust base. Filter plate with five slender setae. Limb V (Fig 4 O). Pre-epipodite subrectangular and densely setulated. Epipodite oval, with a long projection. Exopodite moderately wide, not divided into lobes and armed with four plumose setae; setae 1 – 3 similar in length; fourth seta about 3.4 times shorter than third seta. Internal lobe very wide, oval, bearing long setulae; two setulated setae on inner face of this lobe, one about two times longer than the other. Gnathobase setulated, armed with a curved element; a filter comb absent. Male, ephipial female and ephipium. Unknown. Variability. We observed variability in the morphology of lateral head pores (Figs 3 E – I). In smaller individuals, we observed variability in the spine length of the first segment of endopodite of antenna II (Fig 3 P). In juveniles, a variation was observed in the proportion of the IDL setae (Figs 4 C – D). Differential diagnosis. Anthalona neotropica sp. nov. is a member of the simplex - branch and differs from the other more specialized species in IDL setae armed with fine setulae (Figs 4 C – D) (see Van Damme et al. 2011; Sinev & Kotov 2012). Anthalona neotropica sp. nov. resembles A. sanoamuangae Sinev & Kotov, 2012 and A. simplex Van Damme, Sinev & Dumont, 2011 but differs from A. sanoamuangae in: (1) carapace setae organized in three groups; (2) spine on the first segment of endopod of antenna II very long and almost reaching the end of the third segment; (3) main head pores of similar size; (4) IDL setae of similar length; (5) setae 5 – 6 of limb IV with markedly different length and (6) pecten of postabdominal claw organized in two groups. Anthalona neotropica sp. nov. can be differentiated from A. simplex by: (1) long spinulae on the base of terminal claw; (2) spine on the first segment of endopodite of antenna II very long and almost reaching the end of third segment; (3) IDL setae of similar length; (4) setae 5 – 6 of limb IV with markedly different length and (5) first flaming-torch of limb IV robust. In contrast to other species of the simplex - branch, Anthalona neotropica sp. nov. has the apex of scrapers 6 – 8 markedly curved (Figs 4 E, G – H). More similarities and differences are presented in Table 1.

Diagnosis. Female. Of medium size for the genus, length 0.30 – 0.37 mm, elongated, about 1.6 times as long as high. Head presenting ocellus and eye of similar size; two connected main pores of similar size, underneath sack of lateral head pores lobed (cosmaria). Labral keel without setulae, notches or denticles. Carapace covered by longitudinal lines at posterior region; 31 – 37 naked setae on ventral valve margin. Antennule 2.5 times longer than wide; aesthetascs exceeding the length of the antennule. Antenna II with antennal formula: spines 001 / 101; setae 113 / 003; first segment of the exopod with one cluster of long setulae; a spine on first segment of endopod exceeding the middle-length of the second segment; apical spines of similar length. Postabdomen relatively short, postanal margin rounded with 5 – 6 denticles; 5 – 6 lateral fascicles present; first spinule of each fascicle longer and thicker than the others; all fascicles exceeding the postanal margin. Postabdominal claw longer than the anal margin, with a group of at least three long spinules at the base; claw pecten divided in two groups; basal spine armed with spinules along its dorsal margin. Limb I: ODL with a thin seta; IDL (en 4) with setae 2 – 3 of similar length, bisegmented and armed with thin setulae. Limb II: exopodite without seta, scrapers 7 – 8 with bent apexes. Limb III: exopodite with six setae, setae 1 – 2 of different length; basal endite armed with a sensillum near the first soft seta. Limb IV: exopodite with six setae, sixth seta markedly shorter than fifth seta, first flaming-torch seta robust. Limb V: exopodite with setae 1 – 3 long and plumose, seta 4 short, gnathobase armed with a curved element.

Distribution and ecology. Anthalona neotropica sp. nov. was observed only in Brazil and Argentina (Fig 6 D). It is possible that it has as wide distribution range, as A. verrucosa verrucosa, A. acuta and A. brandorffi. Anthalona neotropica sp. nov. seems to be present in low density in ponds and other lentic ecosystems. However, it was observed with relatively high abundance in samples collected in the hyporheic zone of lotic ecosystems, at depths between 10 and 25 cm. In Central Brazil, A. neotropica sp. nov. was only observed in hyporheic habitats of lotic ecosystems, once few specimens could be removed from the sediments by a water flow. Such as A. simplex and A. sanoamungae, A. neotropica sp. nov. is less specialized than other species from the genus, and probably is a fine sediment dweller, adapted to collect fine materials, such as food. The morphology of IDL setae, presence of a cluster of long setulae on the first segment of exopod of antenna II and the long and thick spine on postabdominal lateral fascicles, confirms its preference for benthic habitat (see Kotov 2006). Notes on the biogeography and relationship between species of the simplex - branch. Anthalona neotropica sp. nov. is a new member of the simplex - branch, which includes also African A. simplex and Asian A. sanoamuangae. The following synapomorphies support the simplex - branch: (1) IDL setae armed with thin setulae; (2) exopodite of limb II without setae and (3) cluster of setulae on the first segment of exopod of the antenna II. In addition, species from the simplex - branch share long lateral spinules on postabdominal lateral fascicles and very plumose long setae on limbs IV and V (Van Damme et al. 2011; Sinev & Kotov 2012). The affinities of A. neotropica sp. nov. with other species of the simplex - branch are obvious, i. e.: Anthalona neotropica sp. nov. and A. sanoamuangae have similar morphology of the underneath sacks of lateral head pores; length of aesthetascs of antennule; marked pre- and postanal angles of postabdomen; similar limbs I, III and V and robust flaming-torch on limb IV. However, the main head pores of different sizes is a unique trait of A. sanoamuangae (Sinev & Kotov 2012). Anthalona neotropica sp. nov. and A. simplex have the same morphology of main head pores, armature of ventral setae of carapace, pecten on postabdominal claw organized in two groups and similar limbs I, III and V (Van Damme et al. 2011). In the simplex- branch, circular sacks of lateral head pores and short and thin first flaming-torch seta on limb IV are morphological traits exclusive of A. simplex. It is known that A. sanoamuangae only occur through South-East Asia (Thailand, Vietnam and Laos) and that A. simplex was only recorded from Congo (Africa) (Van Damme et al. 2011; Sinev & Kotov 2012). Thus, the distribution of the species from the simplex - branch point to a tropical range and could suggest a divergence from the disjunction of the zones connected in the past. Usually such pattern is associated with the Gondwana disruption (see Bayly 1995; Fernando et al. 1987; Dumont & Negrea 2002), although some investigators have serious doubts in " Gondwanian " interpretation of such distributional ranges (Korovchinsky 2006). Morphology of A. neotropica sp. nov., A. sanoamuangae and A. simplex is very conservative, without important reductions or specializations (possibly due to association with similar habitat) that can be used as an argument pro close in-group relationships.

Etymology. The species name derives from the zoogeographical region where the species is found. Anthalona neotropica sp. nov. is the first species of the simplex - branch described for the Neotropics.

Type locality. Sobradinho Stream (15 ° 38 ' 27 " S, 47 ° 46 ' 40 ” W), Distrito Federal, Brazil. Type material. Holotype: undissected adult parthenogenetic female in a tube, preserved in 92 % ethanol solution, deposited at the Museum of Zoology of the University of São Paulo under the accession number MZUSP 33195. The label of the holotype is: “ Anthalona neotropica, 1 parth. ♀ from to Sobradinho Stream, Distrito Federal, Brazil. Holotype ”. Paratypes: Distrito Federal. Two parthenogenetic females from São Bartolomeu River (15 ° 47 ' 34.7 '' S, 47 ° 41 ' 28.2 '' W), Planaltina, Distrito Federal, Brazil, collected by GEEA on 26.08.2006, (CLLA 194 – 195; FDRS 0370). Three adult parthenogenetic females from Sobradinho Stream (15 ° 38 ' 27 " S, 47 ° 46 ' 40 ” W), Distrito Federal, Brazil, collected by GEEA on 5.09.2008 and 0 6.03.2009 (CLLA 177 – 186, 192; FDRS 0371). An adult parthenogenetic female from Pipiripau Stream (15 ° 33 ' 45,5 '' S, 47 ° 30 ' 39,7 '' W), Distrito Federal, Brazil, collected by GEEA on 17.03.2009 (FDRS 0372). Goiás. A juvenile parthenogenetic female from Cachoeira do Palmito (15 ° 51 ' 8.5 " S, 48 ° 57 ' 58.1 " W), Pirenópolis, Goiás, Brazil, collected by LMAEL on 0 1.10.2000 (CLLA 193). Rio de Janeiro. Six parthenogenetic females from hyporheic zone in Solidão River (22 º 57 ’ 36.89 ” S, 43 º 17 ’ 1870 ” W), Tijuca National Park, Rio de Janeiro, Brazil, collected on March / 2012, leg. Ricchardo Mugnai and André Senna (FDRS 0363). Ten parthenogenetic females from the hyporheic zone of the Tijuca River (22 ° 57 ' 13.08 " S, 43 ° 16 ' 55.45 " W), Tijuca National Park, Rio de Janeiro, Brazil, collected on June and November / 2012 (CLLA 187 - 189; FDRS 0365; 0367 - 0369). Rio Grande do Sul. A parthenogenetic female from Machadinho reservoir (27 ° 32 ' 26.71 " S, 51 ° 37 ' 52.31 " W), Upper Uruguai River, Machadinho, Rio Grande do Sul, Brazil, collected by Danilo Augusto Naliato on 0 1.06.2010 (CLLA 190 - 191). Argentina. Two juvenile females from a lateral lake of Lower Paraná River (33 ° 40 ′ 49.00 ʺS, 59 ° 38 ′ 48.80 ʺW), San Pedro, Argentina, collected by José Roberto Debastiani-Júnior on 14.04.2010 (FDRS 0366).