Systelloderes fueguinus, Pereyra & Pancotto & Coscarón, 2025

Pereyra, Hugo A., Pancotto, Verónica A. & Coscarón, M. Del Carmen, 2025, Description of a new species of Systelloderes (Hemiptera: Heteroptera: Enicocephalidae) from Tierra del Fuego, Argentina, Zootaxa 5620 (3), pp. 477-484 : 478-483

Systelloderes fueguinus sp. nov. ( Figs. 1–5 )

Type material. HOLOTYPE: ♀ / Argentina, Tierra del Fuego 54°33’54.41”S, 66°56’48.00”W / Systelloderes fueguinus sp. nov. / Pereyra, Pancotto & Coscarón det. 2024/ MACN_En 2144 / Collection of Museo Argentino de Ciencias Naturales Bernardino Rivadavia . PARATYPES: 1 ♂ / same locality data as holotype/ Systelloderes fueguinus sp. nov. / Pereyra, Pancotto & Coscarón det. 2024/ MACN_En 2145 / Collection of Museo Argentino de Ciencias Naturales Bernardino Rivadavia . 1 ♀ / same locality data as holotype/ Systelloderes fueguinus sp. nov. / Pereyra, Pancotto & Coscarón det. 2024/ MFM/ Collection of Museo del Fin del Mundo .

Description

Measurements of body parts and appendages are provided in Table 1 .

Body moderately small, elongated and covered with varied length setae ( Fig. 2 ).

Colouration. ( Fig. 2 ). Fore lobe of head, collum and hind lobe of pronotum dark brown. Hind lobe of head, post-occipital region, middle lobe of pronotum, and scutellum brown. Labial segments, antennae, and legs yellowish brown. Fore wings and abdomen whitish, lighter than rest of body, with dark brown sclerotised spots.

Cuticle. Head, scutellum and legs shiny and smooth.Thorax and forewing membrane lustrous. Thorax irregularly covered with minute non-setigerous cuticular granules, more densely covered ventrally than dorsally. Abdomen with sclerotised spots.

Vestiture. Sparse, yellowish, consisting of two types of setae (long and short), distributed all over body.

Head above covered with small setae directed anteriorly, and fewer longer erect setae directed slightly anteriorly. Hind lobe and labial segments with longer setae. Antennae and labial segments with longer erect and semi-erect setae, closer to the terminal region of each segment. Post-occipital region lacking setae. Thorax ventrally with caudally inclined setae.

Pronotum with evenly distributed short setae. Long erect setae on anterior region slightly inclined anteriorly, long setae on posterior region, slightly inclined caudally, and denser on remainder of head. Scutellum long setae directed posteriorly, denser than on pronotum. Forewings with short setae distributed over wing veins, marginal veins with distally directed setae, median veins laterally inclined setae, wing membranes without obvious setae. Abdomen with high density of small caudally directed setae, last segments with more long erect setae.

Legs with small, distally inclined setae. Inner sides of femur and tibia with small, sparsely distributed setae. Dorsal side with more erect, slightly distally inclined setae, ventral side with more inclined setae. Dorsal side of femur of the first pair of legs with fewer long setae.

Structure. ( Figs. 2–5 ). Head elongated with well differentiated lobes, fore lobe two times longer and slightly darker than hind lobe. In dorsal view, the anterior lobe subcylindrical, widening towards antennifer. Length of eye 60% of distance to eye and apex of antennifer, protruding 0.050 mm from head, postocular impression very pronounced. Hind lobe almost 1.5 times wider than long ( Fig. 3 ), dorsal margin and laterals globular, convex, ventrally widening to posterior region ( Fig. 4A ). Ocelli small, located in front region of hind lobe with small ocellar tubercles close to lateral margins. In lateral view, maximum height of head 0.353 mm, minimum height 0.203 mm, height across eye 0.272 mm (male, height across eye 0.255 mm). Eyes medium size, close to ventral outline of head in lateral view, longer and widened in upper zone, occupying 43% (male 57%) of head height ( Fig. 4A ). Slender cylindrical antennae, the total antenna length greater than length of head and pronotum together, measuring just under half total length of body, with segments of different sizes, segment II longest followed by III, IV and I, ratio 1.00:2.41:2.18:1.68 (male, 1.00:2.49:2.15:1.90). Four labial segments, segment III longest, widened from mid to distal region ( Fig. 4A ), followed by IV, II and I, segment I and II subtrapezoidal widened in the distal region, segment IV conical, proportions 1.00:1.51:2.70:1.61 (male, 1.00:1.65:2.96:1.85), post-occipital region developed with sublobular shape, width subequal to anterior lobe and one third of length of posterior lobe.

Pronotum subtrapezoidal, 1.3 times wider than long, three lobes clearly separated by transverse constrictions. Constriction dividing collum and middle lobe is concave, deep, and half width of collum length. Collum length one-third of width, shallow longitudinal central impression, deep V-shaped lateral constriction, lateral margins globose, maximum width slightly posteriorly directed ( Fig. 3B ), anterior margin concave, posterior margin convex; in lateral view, upper margin convex, lower margin concave, with a protuberance at the middle of lobe 1+ 1 in granular form, diameter of 0.024 mm, height approximately 0.012 mm ( Fig. 4 ). Middle lobe twice as wide as long, pronounced longitudinal median impression from front impression to just over halfway along lobe where it bifurcates into an inverted Y-shape with less pronounced ramifications, divides lobe into two subquadrangular parts slightly widened posteriorly, two deep lateral pits in anteromedial region directed laterally. Middle and hind lobe constriction shallow, well-defined, semi-straight, anteriorly directed laterally. Hind lobe broader at base, six times wider than minimum length (median region), three times wider than maximum length (lateral region), lateral margins subglobose widened at base, anterior margin semi-straight, posterior margin concave, slightly depressed. Scutellum triangular, slightly convex.

Legs medium-sized, fore legs markedly more robust. In dorsal view margins of F1 and Ti1 of anterior legs subcylindrical, rounded anteriorly and posteriorly. In lateral view; F1 with straight inferior margin, concave superior margin, slightly more than three times longer than wide, Ti1 subtriangle ( Fig. 4A ), widened distal region, more than three times wider as long. Apicitibial armour ( Fig. 4B ) composed of seven spiniform setae: three middle (subequal in linear arrangement, two marginal slightly directed to sides, central straight and slightly longer), two subventral (straight, smaller than the middle, slightly directed to sides), two subdorsal (curved almost 90° from middle spines, directed to tarsus). Ta1 subcylindrical, almost twice as long as wide, distal part of tarsus with tarsal armour formed by four spiniform setae, 1+1 proximal setae curved towards apex, two distal setae external seta similar to proximal setae, internal seta semicircular. Two long claws at apex of tarsus, curved, internal claw longer than external.

Middle and hind legs long and slender, middle legs shorter than hind legs, F2 five times longer than wide, Ti2 cylindrical in dorsal view, slightly widened distally, ten times longer than wide, with two long apical setae and short setal comb formed by eight small setae, Ta2 more than three times longer than wide, with two small isomorphic apical claws, slightly oblique, slightly diverging to sides. F3 wider and longer than F2, 6.50 times longer than wide, Ti3 more than eleven times wider than long with two apical setae and short setal comb, Ta3 five times longer than wide, with two isomorphic apical claws.

Forewings macropterous in male and sub-macropterous in females. Venation typical for Systelloderes .

Abdomen as in other species of Systelloderes , female with 1+1 large sclerites in lateral region of each segment ventrite and tergite, male with more sclerotised tergites and ventrites. Genitalia visible externally, male ( Fig. 5A ), female ( Fig. 5B ). Abdomen broadened in ovigerous female ( Fig. 5C ).

Male similar to female, elongate, overall size smaller, eyes larger, forewings macropterous ( Fig. 2A ).

Differential diagnosis. Systelloderes fueguinus sp. nov. is distinguished from other South American species by the shape of the posterior lobe of head, which is wider than long. Posterior lobe of head in six previously recorded species of Systelloderes ( S. moschatus Blanchard, 1852 from Chile; S. spurculus Stål, 1860 from Brazil; S. longiceps Jeannel, 1943 from Peru; S. harroyi Villiers, 1952 and S. guigliae Villiers, 1968 from Venezuela; S. tortonesei Villiers, 1968 from Bolivia) is longer than wide, except S. harroyi , which has posterior lobe wider than long and is the only one with a trapezoidal-shaped lobe. S. fueguinus sp. nov. differs from S. moschatus (morphologically and geographically closest species, occurring in north-Patagonia, Chile) ( Figs. 1A and 3A ) by the following characters: pronotum always wider at base than maximum length (pronotum slightly longer than maximum width in S. moschatus ); smaller eye, occupying 43–57 % of head width in lateral view (larger eye occupying 75% of head width in lateral view in S. moschatus ); small ocelli of 0.04 mm diameter and larger interocellar distance (ocellus of double size and shorter interocellar distance in S. moschatus ); collum more lobulate with the suture dividing the first and second lobes slightly more defined than in S. moschatus ( Fig. 3 ).

Etymology. The new species is named after the Argentinean province ‘Tierra del Fuego’, where it was found.

Distribution and habitat. Systelloderes fueguinus sp. nov. is the first Subantarctic and the second Argentinian species recorded of the genus Systelloderes . It was collected only in forested peat bogs, Sphagnum dominated, in the central region of Tierra del Fuego Island ( Fig. 1 ).

Figures

FIGURE 1. A. Distribution of the six recorded species of Systelloderes in South America (also including unidentified species (S. spp.) from Colombia and Ecuador). B. Habitat where the samples were collected (transition of the peat bog-forest near Ginebra River.

FIGURE 2. Adults of Systelloderes fueguinus sp. nov., habitus. A. Male, macropterous. B. Female, submacropterous.

FIGURE 3. Comparison of male head and pronotum. A. Systelloderes moschatus. B. S. fueguinus sp. nov. Scale bar: 1 mm.

FIGURE 4. Systelloderes fueguinus sp. nov., male paratype. A. Lateral view of body.Arrow indicates pronotum protuberance. B. Apicitibial and tarsal armature (internal view).

FIGURE 5: Systelloderes fueguinus sp. nov. (A and B, ventral view. C, lateral view). A. Male external genitalia. Arrows indicate parameres. Py, Pygophore. B. Female external genitalia. Arrow indicates fused 8th and 9th segments. C. Ovigerous female abdomen and adjoining parts.

Tables

TABLE 1. Systelloderes fueguinus sp. nov., measurements (in millimetres) of body parts and appendages of male and females.

Key feature	Male	Females	Key feature	Male	Females
Body total length	3.296	4.693–4.765	Middle lobe pronotum length	0.292	0.303–0.318
Body width	0.874	0.725–1.040	Middle lobe pronotum width	0.558	0.611–0.672
Head length	0.770	0.799–0.884	Hind lobe pronotum minimum length	0.116	0.130–0.141
Head width	0.317	0.336–0.346	Hind lobe pronotum maximum length	0.231	0.232–0.239
Fore lobe minimum width	0.198	0.211–0.235	Hind lobe pronotum width	0.705	0.743–0.865
Fore lobe length	0.440	0.437–0.471	Fore wing length	1.790	1.860–2.386
Hind lobe length	0.218	0.230–0.263	Fore wing maximum width	0.630	0.602–0.816
Hind lobe width	0.317	0.330–0.339	Fore femur length	0.688	0.666–0.829
Head width (across eye, in dorsal view)	0.294	0.314–0.322	Fore femur width	0.218	0.237–0.287
Interocular distance (in dorsal view)	0.186	0.197–0.203	Fore tibia length	0.613	0.626–0.716
Interocular distance (in ventral view)	0.150	0.160–0.179	Fore tibia width	0.181	0.225–0.238
Eye length	0.145	0.114–0.117	Fore tarsus length	0.163	0.162–0.199
Eye width	0.112	0.099–0.100	Fore tarsus width	0.100	0.091–0.110
Eye Distance—dorsal outline of head (in lateral view)	0.075	0.821–0.882	Internal claw of fore tarsus	0.170	0.164–0.203
Eye Distance—ventral outline of head (in lateral view)	0.035	0.061–0.066	External claw of fore tarsus	0.150	0.152–0.183
Eye proportion (in lateral view)	57%	43%	Middle femur length	0.506	0.528–0.629
Interocellar distance	0.130	0.101–0.117	Middle femur width	0.101	0.118–0.144
Ocellus length	0.030	0.041–0.058	Middle tibia length	0.504	0.491–0.530
Ocellus width	0.040	0.032–0.049	Middle tibia width	0.049	0.074–0.111
1 st labial segment	0.096	0.121–0.140	Middle tarsus length	0.196	0.205–0.246
2 nd labial segment	0.159	0.155–0.183	Middle tarsus width	0.050	0.051–0.080
3 rd labial segment	0.285	0.284–0.311	Middle claw	0.090	0.072–0.108
4 th labial segment	0.178	0.164–0.170	Hind femur length	0.721	0.760–0.879
1 st antennal segment	0.203	0.197–0.220	Hind femur width	0.105	0.199–0.239
2 nd antennal segment	0.506	0.475–0.506	Hind tibia length	0.890	0.866–0.977
3 rd antennal segment	0.436	0.431–0.449	Hind tibia width	0.080	0.094–0.127
4 th antennal segment	0.386	0.330–0.337	Hind tarsus length	0.316	0.318–0.355
Collum length	0.131	0.171–0.192	Hind tarsus width	0.070	0.072–0.081
Collum width	0.366	0.386–0.403	Hind claw	0.090	0.099–0.114