Argentina: Misiones: 1 ♂ (holotype), Puerto Victoria, S26.33441°, W54.65540°, VI.1943, Zenzes leg. (MLP 16710; examined); 1 ♀, Iguazú National Park, Centro de Investigaciones Ecológicas Subtropicales, -25.67859°, -54.44927°, 20.IX.2014, G.D. Rubio leg. (IBSI-Ara 00198; tissue sample GDR 4126); 1 ♂ and 1 ♀, same locality, 17.X.2014, G.D. Rubio leg. (IBSI-Ara 00207); 2 ♀, same locality, 4.III.2015, G.D. Rubio leg. (IBSI-Ara 00291; tissue sample GDR 4143); 1 ♂, Puerto Iguazú, -25.59351°, -54.56968°, 20.XII.2014, J. Baigorria leg. (IBSI-Ara 00246).

Specimens of B. nigrosecta resemble B. picta Peckham & Peckham, 1894 and B. reducta Chickering, 1946 in general body coloration (Chickering 1946; Edwards 2006: figs 115, 118, 123), and in general structure of epigyne, having an anterior atrium with narrow sclerotized rims of the copulatory openings on the posterior edge of the atrium (Figs 4, 5; arrow, rim of CO) (Chickering 1946: fig 47; Edwards 2006: fig 116), respectively. It can be distinguished from B. picta by having a larger atrium, with the copulatory openings (CO) farther apart, anteriorly concave, and nearly transverse in orientation (B. picta has the COs nearly touching, anteriorly convex, and strongly oblique in orientation), and a thinner and curved male retrolateral tibial apophysis (Figs 1, 4, 5; compare with Edwards 2006: figs 116, 121, 122, 126). Also, the “W” shaped transverse mark across the middle of the abdomen is distinctive for both sexes, as only the lateral parts of this mark are evident and the medial connecting parts are absent for B. picta. It can be distinguished from B. reducta by having the copulatory ducts (CD) contiguous along the mid-line of the body in the middle of the duct (Fig. 5; compare with Chickering 1946: fig 47).

Figure 1–5. 

Balmaceda nigrosecta Mello-Leitão. 1 Male palp, ventral view (inset with close-up of RTA in retrolateral view) 2 female, lateral habitus 3 same, dorsal habitus 4 epigyne, ventral view 5 same, cleared. (AG–accessory gland; AT–atrium; CD–copulatory duct; CO–copulatory opening; E–embolus; FD–fertilization duct; RTA–retrolateral tibial apophysis; S–spermatheca; SP–spermophore; T–tegulum). Scale bars: 0.35 mm (1); 3 mm (2, 3); 0.2 mm (4, 5).

Female from Iguazú National Park (IBSI-Ara 00207) (Figs 2–8). Total length: 7.84. Carapace length: 3.10; width: 2.44; height: 1.00. Carapace low, reddish brown, darker toward the borders and in the cephalic region, covered with white scales and sparse black hairs (Figs 6–8). Length of the dorsal eye field: 1.30. Width of the anterior eye row: 1.65; posterior: 1.45. Clypeus very low (0.05 height), with white hairs. Chelicera dark orange, vertical, with two teeth on promargin and one bicuspid tooth on retromargin. Labium and endites brown, sternum lighter. Palp yellow. Leg I stout, especially tibia and femur. Legs 4123, light brown with scattered dark spots usually where legs articulate, covered with sparse black hairs. Prolateral ventral margin of leg I spotted with brown, mainly on femur, patella and proximal tibia. Femur I 1.68×0.76; II 1.45x0.60; III 1.32; IV 1.67. Patella I 1.15; II 0.92; III 0.80; IV 0.97. Tibia I 1.25x0.42; II 1.00x0.35; III 0.83; IV 1.45. Metatarsus I 0.82; II 0.80; III 0.92; IV 1.09. Tarsus I 0.42; II 0.42; III 0.50; IV 0.52. Leg macrosetae: femur I, II d 1-1-p1, p 0-1-2(d1+v1); III d 1-1-p1, r 0-1-2(d1+v1); IV d 1-1-1. Tibia I v 2-2-2, p 0-1; II v 2-2-2; III, IV v p1di; Metatarsus I, II v2-2; III, IV v 2di, r 1di, p 1di. Abdomen length: 4.20; width: 2.32. Abdomen oval, with sparse black hairs; coloration pale yellow with a brown irregular W-shaped mark in middle of dorsum (Figs 6–8); margins spotted with brown, and four short bands inclined posterolaterally (Figs 6–8); venter pale yellow. Epigyne (Figs 4, 5): epigynal plate large, with a broad anterior atrium (a wide, shallow concavity); atrium shaped like a broad inverted V, each branch of which intersects (in a position just anterior to median) a slightly oblique slit-like copulatory opening that has a narrow strongly sclerotized rim (Fig. 5); copulatory ducts short, with a 180° bend backwards, connecting to a spherical spermatheca. An accessory gland (AG) occurs posterior to copulatory opening at posterior end of copulatory duct head (region of duct from CO to gland and first bend in duct). Fertilization duct anterior to spermatheca (Fig. 5). Spinnerets pale yellow. Variability: without significant variation in color pattern (n=4), otherwise total length: 6.19–7.84; carapace length: 2.65–3.10, width: 2.15–2.44, height: 0.87–1.12; abdomen length: 3.36–4.80, width: 1.70–2.70; epigynal plates may vary slightly in amount of sclerotization, and some abdomens are more pigmented than others.

Figure 6–11. 

Balmaceda nigrosecta Mello-Leitão, habitus of living specimens from Iguazú National Park. Female (6–8); male (9–11).

Male (Holotype, MLP 16710): See Mello-Leitão (1945: 277) and Edwards (2006: 211, figs 123–126). Left palp as in figure 1, habitus as in figures 9–11.

From the illustrations in the original description it is clear that this species is very closely related to B. reducta (Chickering 1946: 64), and B. nigrosecta possibly is a senior synonym of B. reducta. Because the known distribution of B. reducta is limited (Panama) and far from Argentina, no synonymy will be made, as the genus is not yet adequately sampled in the region.

Because we note that the morphological data are quite similar among members of the genus, it is difficult to establish an intersexual autapomorphy (see Edwards 2014) for B. nigrosecta. Nevertheless, it appears that the irregular W-shaped mark in the middle of the abdominal dorsum is a species shared autapomorphy(Figs 6–11). Sex matching is also supported by geographic and phenological evidence, and by an instance of both sexes co-habiting in the same retreat, where an adult male and an adult female were found together.

Balmaceda nigrosecta has sexual dimorphism as frequently occurs in other salticids, althoughstrong dimorphism is uncommon in marpissines. In this case the sexual dimorphism is weak; the males only show a slightly darker color in palps and first pair of legs. They live in many parts of the peri-urban area (Fig. 12), even on light poles. They make a flat retreat or nest, about 15 mm long, always placed perpendicular to the ground, between 1 and 2 meters above ground (Figs 13–17). The entrance opening can be on either side. Spiders are positioned at the entrance, with the carapace leaning out (Figs 15, 16), usually looking down (as figure 16). In fifty-one observations, we saw them hunt in the same way: locate prey from the retreat or while actively searching (sometimes we observed them walking in the vicinity of the retreat in search of prey); when they detected something moving, they would accelerate towards it. Here one of two things would happen: if it was an unpalatable prey (e.g. an ant), spiders did not attack and returned quickly to the retreat; but if it was a potential prey, the spiders accelerated a definite distance, about 10 body lengths, and then lowered themselves close to the substrate, and continued approaching very slowly, like a cat stalking, then jumped extremely quickly over the prey. The catch was always observed to be successful, in one movement.

Figure 12–17. 

Habitat and natural retreat of Balmaceda nigrosecta Mello-Leitão. Puerto Iguazú (12), Iguazú National Park (13–17). Note the typical stalking position in 16.

Only known from northeast Argentina, in Misiones Province.