Liocanthydrus nanops Baca 2014

Liocanthydrus nanops Baca et al., 2014 Figs 1–8, 9–12, 16, 18–20, 21–27, 28–29, 30–33, 34–37, Tables 1, 2 Material examined. Argentina – Misiones Province: 2 ♂ and 4 ♀, Iguazú National Park, 25°40'S, 54°27'W, 27. IX. 1997, López Ruf leg. (LEBA) • 1 larva of instar III and 19 adults, Iguazú National Park, Daniel “Pupi” Somay bird observatory, 25°42'54"S, 54°26'54"W, alt. 197 m a. s. l., 9. I. 2024, Urcola leg. (LEBA) • 1 larva of instar I and 18 adults, same data except 10. I. 2024 (LEBA). Measurements. TL = 2.8–3.10 mm, mean = 2.95 mm; GW = 1.35–1.50 mm, mean = 1.4 mm; TL / GW = 2.0– 2.2 mm, mean = 2.1 mm; HW = 0.85–0.95 mm, mean = 0.9 mm; EW = 0.5–0.65 mm, mean = 0.55 mm; HW / EW = 1.5–1.7 mm, mean = 1.55 mm; PNWant = 0.85–1.0 mm, mean = 0.95 mm; PNWpost = 1.3–1.5 mm, mean = 1.35 mm; PNWpost / PNWant = 1.4–1.5 mm, mean = 1.45 mm; TLVP = 1.15–1.3 mm, mean = 1.2 mm. Variation in adult morphology. Similar to what was reported by Baca et al. (2014), the specimens examined here show considerable variation in color. Many of the specimens exhibit a yellow head and pronotum, whereas in others these parts are reddish brown. The dark macula on the anteromedial region of the pronotum (Fig. 1) is absent in some individuals. Most of the specimens have dark elytra with clearly visible yellow spots (Fig. 1), while in others the elytra are dark reddish brown and the spots are only slightly lighter. The specimens collected in 1997 have a reddish-brown head and pronotum, the latter lacking the dark anteromedial macula, and the elytra are slightly darker with the spots barely visible (similar in color to the head and pronotum). However, examination of the aedeagus revealed the same diagnostic characters as reported by Baca et al. (2014) and the other specimens collected here. Finally, the two males collected in 1997 have the anterodorsal margin of sternite IX widened, similar to that reported by Grosso (1979) for specimens identified as L. octoguttatus. However, we observed that this character is variable in the rest of the material examined, with this widening absent in most specimens (Fig. 3). Remarks. Based on Grosso’s (1979) redescription and drawings of the male genitalia of the specimens alleged to be L. octoguttatus (Figs 9–12, modified from original drawings), we can observe that the left lateral lobe has a well-projected distal angle (Fig. 11). The only known species of Liocanthydrus in which the left lateral lobe has this shape is L nanops (Baca et al. 2014) (Fig. 5), which is also the only species distributed near the area where the specimens studied by Grosso were collected (Fig. 17). This evidence, summed to the shape of the apex of the median lobe in lateral view (Fig. 12) led us to conclude that the specimens studied by Grosso belong to L. nanops. It should be noted that, when Grosso identified his material, L. nanops had not yet been described. Grosso likely relied on Zimmermann’s (1921) treatment of L. octoguttatus, which lacks a description of the male genitalia (a crucial feature to recognize that it belongs to a distinct species given the very similar external appearance of both species). Habitat and co-occurring taxa. Adults and larvae of L. nanops were collected in a stream floodplain with other noterid species: Hydrocanthus socius Sahlberg, 1844, Suphisellus balzani (Régimbart, 1889), and S. rufipes (Sharp, 1882). The sampling site was mostly exposed to sunlight, had a muddy bottom, shallow depth, slow current, cool water, and abundant emergent vegetation (Figs 13–15). Distribution. Argentina (Formosa, Misiones) (new record), Brazil, and Paraguay (Fig. 17). Description of larva. Instar I (Figs 18 – 33). Color. Entirely testaceous. Body. Elongate, nearly parallel sided (Fig. 18). Measurements and ratios that characterize the body shape are given in Table 1. Head. Prognathous; cephalic capsule (Figs 19, 20) slightly longer than broad; maximum width posterior to stemmata; slightly narrowed posteriorly; occipital foramen large; coronal suture very short; ecdysial suture U-shaped; tentorial pits visible postero-ventrally, well separated from each other and from occipital foramen; six lateral stemmata arranged in two curved vertical rows at each side. Frontoclypeus elongate, roughly subovate, anterior margin rounded, with two spine-like egg bursters on basal third. Antenna (Figs 21, 22). Short, robust, shorter than maximum head width, composed of four antennomeres; A 2 and A 3 longest, subequal; A 3 with a rugged area on distal portion; A 4 approximately 3 / 4 length of A 3; A 1 shortest. Mandible (Fig. 23). Symmetrical, short, basal half broad, inner margin with strong subrectangular process, distal half slender, curved inwards, narrowing to pointed apex, inner margin smooth. Maxilla (Figs 24, 25). Cardo small, suboval; stipes well developed, subtrapezoidal, bearing a galea on distal inner margin and a palpus on distal outer margin; galea well developed, composed of two galeomeres, GA 2 more slender and subequal in length to GA 1; palpifer not cleary differentiated from stipes, more evident in ventral view; palpus short, robust, composed of three palpomeres, MP 1 shortest, MP 3 longest. Labium (Figs 26, 27). Prementum well developed, subrectangular, somewhat broader than long, anterior margin narrowly indented medially; palpus short, robust, composed of two palpomeres, LP 2 longer than LP 1. Thorax. Terga fully sclerotised, convex (Fig. 18); pronotum about as long as meso- and metanotum combined, meso- and metanotum subequal in length, approximately as wide as pronotum; protergite subrectangular, lateral margins rounded, more developed than meso- and metatergite; meso- and metatergite with anterotransverse carina; ecdysial line absent. Legs (Figs 28, 29). Short, robust, composed of six articles, L 1 shortest, L 3 longest; coxa broad, elongate, trochanter lacking annulus, femur, tibia and tarsus short, subcylindrical, pretarsus with two long, slender, slightly curved claws, posterior claw slightly shorter than anterior claw. Abdomen. Eight-segmented (Fig. 18); segments I – VIII completely sclerotised, ring-like, progressively narrowing to apex, with anterotransverse carina; segment VIII (Figs 30, 31) the longest and narrowest, with two terminal dorsal projections, lacking a U-shaped wavy membranous area ventrally, contiguous to urogomphi; siphon absent. Urogomphi (Figs 32, 33). Short, cylindrical, visible in dorsal view (Fig. 18), not fused to each other. Chaetotaxy. Similar to that of L. clayae (see Urcola et al. 2021) except for the following features: seta FR 1 very short (Fig. 19); seta PA 9 absent (Fig. 19); seta AN 1 inserted more distally (Fig. 21); seta MN 1 short (Fig. 23); MP 3 with several minute sensilla on surface (Figs 24, 25); pore URa located on dorsal surface (Fig. 32). Setae on abdominal segment VIII were not named in instar II of L. clayae due to the presence of secondary setae. Therefore, they are detailed here for L. nanops: dorsal surface of segment VIII with one seta (AB 1) on basal region, one seta (AB 3) on distal third and one long (AB 4) and four minute (AB 5, AB 6, AB 7, AB 16) setae apically (Fig. 30); each terminal dorsal projection with one short medial seta (AB 14) and one long apical seta (AB 8); ventral surface of segment VIII with two setae (AB 12, AB 13) on basal region and four setae (AB 9, AB 10, AB 11, B 15) on distal region (Fig. 31). Instar III (Figs 16, 34–37) As for instar I except for the following features: Body. Measurements and ratios that characterise body shape are shown in Table 1. Head. Egg bursters absent; A 2 longer than A 3; A 4 shortest, approximately 1 / 2 length of A 3; mandible more robust, process less prominent (Fig. 34). Abdomen. Siphon relatively long, slender, apex truncated (Fig. 37). Chaetotaxy. Frontoclypeus with 14–21 minute secondary setae on anterior half and 3–4 minute secondary setae on posterior half; dorsal surface of parietal with seta PA 9 present (inserted close to seta PA 6), 0–4 minute secondary setae on anterior portion and 10–13 minute secondary setae on posterior portion (Fig. 34); ventral surface of parietal with 10–13 minute secondary setae on anterior half and 1–2 minute secondary setae on posterior half; secondary leg setation detailed in Table 2 and Figs 35, 36; abdominal segments I – VII with several secondary setae; dorsal surface of abdominal segment VIII (Fig. 37) with three elongate hair-like secondary setae and 2–3 minute secondary setae on anterior portion, 2–3 minute secondary setae on medial portion, and five hair like-like secondary seta and 4–5 minute secondary setae on posterior portion; ventral surface of abdominal segment VIII with two elongate hair-like secondary setae on anterior portion, one elongate hair-like secondary seta on medial portion, and one short and one long secondary setae on posterior portion. Remarks. When comparing the first and third instars of L. nanops with the supposedly third instar of L. clayae (Urcola et al. 2021), we can conclude that the larva of this latter species is actually a second instar. This conclusion is based on the following evidence: the head of the larva of L. clayae (as expressed in the head width) exhibits an intermediate size between the first and third instars of L. nanops; the mandibles in L. clayae are not as robust as those of the third instar of L. nanops; and the siphon in L. clayae is more developed than that of the first instar of L. nanops but not as strongly developed as that of the third instar of this species. Regarding chaetotaxy, seta PA 9 is absent on the parietal of the first instar of L. nanops. This conspicuous sensillum, however, is present in the third instar of this species (Fig. 34), as well as in all noterid larvae known in detail (e. g. Urcola et al. 2019, 2020, 2021). Since we examined only a single specimen of each instar of L. nanops, we prefer not to consider the absence of PA 9 in instar I as a diagnostic character for the species until mor