Ilyobius nubilus
Creators: name: Mendes, Gabriela Caroline
name: Nascimento, Jeane Marcelle Cavalcante Do
name: Fusari, Lívia Maria
name: Hamada, Neusa
Publisher: name: Zenodo
Year: 2024
Subjects: Biodiversity
Taxonomy
Animalia
Arthropoda
Insecta
Megaloptera
Sialidae
Ilyobius
Ilyobius nubilus

description: Ilyobius nubilus (Navás, 1933)
(Figs 2–11)
Protosialis nubila Navás, 1933: 36 (original description). Penny, 1977: 9 (cat.); Contreras-Ramos 2008: 808 (taxonomy); Heckman 2017: 78 (key of species).
Ilyobius nubila; Liu et al. 2015a: 31 (phylogeny of Sialidae; comb. nov.); Liu et al. 2015b: 59 (redescription).
Ilyobius nubilus; Oswald, 2018 (cat.).
Type locality: Brazil (São Paulo).
Material examined. 15 males: 5 pinned (INPA), 10 fixed in 80% alcohol (MZUSP), with pupae and exuviae of the last instar in glycerin; 12 females: 5 pinned (INPA), 7 fixed in 80% alcohol (5 in INPA, 2 in MZUSP), with pupae and exuviae of the last instar in glycerin; last-instar (INPA) fixed in 80% alcohol. Brazil, São Paulo State, Salesópolis municipality, Estação Biológica Boracéia, (23°39’07.4’’S, 45°52’33.4’’W) 25.vi.2021; N. Hamada, L. M. Fusari, J. O. da Silva, T. T. S. Polizei cols.
17 males: 7 pinned (INPA), 10 fixed in 80% alcohol (MZUSP), with pupae and exuviae of the last instar in glyceryn; 11 females: 4 pinned (INPA), 7 fixed in alcohol 80% (5 in INPA, 2 in MZUSP), with pupae and exuviae of the last instar in glycerin; 7 last-instar (5 in INPA, 2 in MZUSP) fixed in 80% alcohol. Brazil, São Paulo State, São Luiz de Paraitinga municipality, Parque Estadual Serra do Mar, Núcleo Santa Virgínia (23°21’43’’S, 45°08’15’’W) 24.ix.2021; L.M. Fusari, J.O. da Silva cols.
Female redescription. (Fig. 2) Body length: mean = 9.6 mm (Standard Deviation (SD) ± 0.4, n = 5); forewing length: mean = 11.3 mm (SD ± 0.519, n = 5), width: mean = 3.5 mm (SD ± 0.228, n = 5); hindwing, length: mean = 9.6 mm (SD ± 0.134, n = 5), width: 3.5 mm (SD ± 0.251, n = 5).
Head (Fig. 3A–F). Width (at the widest point): mean = 2.2 mm (SD ± 0.070, n = 5); length: mean = 1.8 mm (SD ± 0.1, n = 5); region between the posterior margin of the eyes: mean = 1.7 mm (SD ± 0.044, n = 5). General color blackish, except by the regions extending laterodorsally from inner margin of compound eyes to the base of the head; coloration of these regions varying from pale orange-brown to orange (Fig. 3A–F); densely covered with yellowish-brown and blackish setae. Antennae with scape, pedicel, and flagellum blackish, densely covered with black setae; 34–35 flagellomeres. Mouthparts blackish brown, densely covered with dark yellowish-brown setae (Fig. 3D–F).
Thorax (Fig. 2A). Pronotum black, subrectangular; width (widest region): mean = 1.94 mm (SD ± 0.114, n = 5), length: mean = 0.84 mm (SD ± 0.054, n = 5); meso- and metanotum blackish, subrectangular, densely covered with short, blackish setae.
Legs (Fig. 2B). Blackish yellow, densely covered with blackish setae.Forefemur shorter than mid- and hindfemur and slightly expanded. Tibial spurs short, brownish. Basitarsi of fore- and midleg short, slightly smaller than second and third tarsomeres together; longer on hindleg, larger than second and third tarsomeres together. Tarsal claws yellowish.
Wings. Membrane translucent dark brown in alcohol and iridescent blackish in vivo, with dark brown veins and densely covered with blackish-brown setae. Forewing (Fig. 12E): 3X longer than wide proximally, 3X longer than wide distally; posterior margin slightly rounded; costal area slightly expanded on proximal 1/3 of the wing length, with 9–11 crossveins; radial area with three crossveins; sc-r present; RP with two branches; M separated from R, bifurcated near middle of the wing; MA not bifurcated; MP bifurcated near posterior margin of the wing; midulnar area with two crossveins; area between M and CuA with three crossveins; CuA bifurcated near posterior margin; CuP not bifurcated; area between CuA and CuP with a single crossvein; 1A not bifurcated, 2A with two simple branches, 3A simple; area between A1 and A2 with a single crossvein; area between A2 and A3 with a single crossvein. Hindwing: 3X longer than wide, similar to forewing, but slightly wider; costal area undilated, with 6–9 crossveins; area between M and CuA with a single crossvein; MA with a veinlet fused to MP proximally; MP not bifurcated; anal area of wing expanded.
Abdomen. Blackish brown, densely covered with blackish setae.
Genitalia (Figs. 4, 5). Sternite 7 with thumb-shaped, median projection posteriorly projected in lateral view (Fig. 4A, B); in ventral view, subtriangular, with posterior margin rounded, slightly projected medially (Fig. 5A–D). Tergite 9 subtrapezoidal, in lateral view, ventral region broadly valvate; joined to upper region by a junction line (Fig. 4A, B). Gonocoxite 8 reduced, represented by a small, setose sclerite in ventral view, located beneath sternite 7 (Fig. 5A–E). Gonapophysis 8 as a single strongly sclerotized plate, ending in two broad semicanals, one at each end; when Gph8 is positioned parallel to the body, in ventral view, distal margin straight with a small concavity medially; proximal margin concave (Fig. 5A, B); when Gph8 is positioned with the proximal margin internally directed (as described in Navás, 1933), in ventral view, distal margin strongly concave medially, proximal margin with slightly concavity medially (Fig. 5C, D). Gonocoxite 9, in lateral view, subrectangular, densely setose, posteriorly with a small gonostylus 9 at apex (Fig. 4A, B). Ectoprocts setose, in lateral view, short and roundly (Fig. 4A, B).
Male description. Body length: mean = 9.1 mm (SD ± 0.494, n = 5); forewing length: mean = 9.8 mm (SD ± 0.198, n = 5), width: mean = 3.18 mm (SD ± 0.130, n = 5). Hindwing length: mean = 8.9 mm (SD ± 0.253, n = 5), width: mean = 3.4 mm (SD ± 0.114, n = 5).
General coloration and external morphology similar to female, general color blackish, except by the regions extending laterodorsally from inner margin of compound eyes to the base of the head; head color variation which was not observed in the males studied.
Head. Width (widest region): mean = 1.9 mm (SD ± 0.041, n = 5); length: mean = 1.37 mm (SD ± 0.083, n = 5); region between the posterior margin of the eyes: mean= 1.5 mm (SD ± 0.047, n = 5); scape, pedicel and flagellum blackish with 31–33 flagellomeres.
Thorax. Width (widest region): mean = 1.8 mm (SD ± 0.074, n = 5); length: mean = 0.8 mm (SD ± 0.021, n = 5).
Wings. Forewing (Fig. 6A): branching condition similar to female; costal area with nine crossveins. Hindwing (Fig. 6B): similar to the forewing; costal area with eight crossveins; MP not bifurcated.
Genitalia (Figs 7, 8). Tergite 9 sclerotized, densely setose; subrectangular, with rounded dorsal margin in lateral view (Fig. 7A); in dorsal view, sub-rectangular; distal margin convex, basal margin concave (Fig. 7C). Sternite 9 trifurcate, sparsely setose, central projection longer than the lateral ones (Fig. 7A, D); in lateral view, central projection with same width along the entire length (Fig. 7A). Endophalic sac membranous, eversible, with several fringed thorny setae (Fig. 8A, B). Gonocoxite 9 robust, setose; in lateral view, subrectangular, rounded distal margin, a small concavity medially (Fig. 7A). Anal tubercle membranous. Ectoprocts paired, robust; in lateral view, rounded; dorsal margins convex, ventral margins straight with proximal margin fused to gonocoxite 11 (Fig. 7A); in dorsal view, internal margin concave (Fig. 7C). Gonocoxite 11 L-shaped in lateral view; dorsally curved; distal region pointed at apex and projected upwards, representing gonostylus 11 (Fig. 7A); gonocoxite 11 divided into two broad sclerites that are medially directed and connected by a membranous region in caudal view, setose; each sclerite with apex curved, directed medially (Fig. 7B).
Mature larvae (Figs. 9–11). Length: mean = 8.7 mm (SD ± 0.128, n = 5); width: mean = 1.98 mm (SD ± 0.204, n = 5).
Head (Fig. 9C, D). Length, from the clypeal margin to distal region of the head capsule: mean = 3.2 mm (SD ± 0.099, n = 5); maximum width: mean = 3.4 mm (SD ± 0.078, n = 5); subquadrate. Orange-brown in color, with a darker horizontal band on anterior region; yellowish digitiform marks on posterior region; strongly sclerotized; muscle scars on posterior half; several thin sparse setae distributed on head capsule (Fig. 9C). Clypeus wide and narrow, 10X wider than long (Fig. 9C). Antenna (Fig. 10d): 4-articulated; first antennomere longer than wide, wider than the others; second antennomere longer than the others, 3X longer than antennomere 1; third antennomere slender, 1.5X longer than antennomere 1; fourth antennomere slender, subequal in size to antennomere 3, apically with short setiform sensilla. Labrum (Fig. 10A) strongly sclerotized, subtriangular, 4.5X wider at the base than apex; basally slightly wider than long; lateral margins concave, with thin setae sparsely distributed in dorsal view; in ventral view, with two pairs of pointed apophyses at tip, inner pair shorter. Mandible (Fig. 10B) symmetrical, slender and long, sharply pointed with a minute basal tooth (difficult to see in specimens with worn mandibles), with two preapical teeth and a sharp terminal tooth, slightly serrated at base; outer margin convex, with basal, thin, long seta, and short, slender seta near midlength. Maxilla (Fig. 10C), in ventral view, with cardo and stipes subtriangular; cardo 2X longer than stipes. Lacinia hook-like, well developed. Galea cone-shaped. Palpifer subrectangular. Palpus: first palpomere wider than long, shorter than the others; second palpomere longer than the others, twice the length of the third; fourth palpomere sub-equal in size to palpomere 3, cone-shaped. Labium (Fig. 10C) with submentum hexagonal in ventral view, slighly longer than cardo; mentum subrectangular, slightly longer than wide, 2X shorter than submentum, with lightly sclerotized areas; prementum slightly wider than long, 1X narrower than mentum; well-developed membranous ligula.
Thorax. Tergites dark brown, with orangish-yellow marks (Fig. 9A). Pronotum: length = 1.8 mm (SD ± 0.071, n = 5); maximum width = 2.8 mm (SD ± 0,087, n = 5); subrectangular, anterior margin slightly rounded, posterior margin straight. Legs (Fig. 11A–F): yellowish. Coxa of all legs slightly longer than wide, with few setae sparsely distributed (Fig. 11A–F). Profemur ca. 3X longer than wide; internal margin with long, thick setae; internal surface with two rows of long setae near external margin (Fig. 11A); external surface with a row of long, thick setae near external margin, and with a row of shorter setae on submedial region (Fig. 11B); mesofemur ca. 3X longer than wide; internal margin with long, thick setae; internal and external surface with a row of long setae near external margin; internal surface with a row of shorter setae near internal margin (Fig. 11C); external surface with a row of short setae on submedial region (Fig. 11D); hindfemur ca. 3.5X longer than wide; internal margin with long, thick setae; internal and external surface with a row of long, thin setae near external margin (Fig. 11E, F); external surface with a row of shorter setae on submedial region and with a row of pectinate sensillae above submedial row of setae (Fig. 11E); internal surface with a row of short setae near internal margin, with a row of pectinate sensillae between the internal margin and the row of setae on submedial region (Fig. 11F). Protibia ca. 2.5X longer than wide; mesotibia ca. 3X longer than wide; foretibia slightly longer than mesotibia. Tibia of all legs with few, long, thick setae on internal and external margins (Fig. 11A–F); external surface of pro- and mesothoracic legs with a row of short, thick setae submedially (Fig. 11B, D); external and internal of metathoracic leg with pectinate sensilla below the submedial row of setae (Fig. 11E, F). Protarsus ca. 3X longer than wide; mesotarsus ca. 4X longer than wide; metatarsus ca. 3.5X longer than wide; internal and external margins of prothoracic and mesothoracic legs with thick setae; external margin with thin setae; external surface with longitudinal row of thick setae on dorsal and ventral margin (Fig. 11B, D); external and internal surface of metathoracic leg with a row of short, thick setae submedially; with pectinate sensilla below the submedial row of setae (Fig. 11E, F). Tarsal claws approximately the same width along the entire length.
Abdomen (Fig. 9A). Poorly sclerotized; light brown; abdominal gills whitish translucent.
Distribution. Brazil (São Paulo).
Remarks. The type locality of Ilyobius nubilus was cited as Mato Grosso State of Brazil in original description as it appears on the unclear handwritten label of the holotype. A different location is indicated on the opposite side of this label, in São Paulo State of Brazil, which was not mentioned in original description (Liu et al. 2015b). Considering the high level of endemism of Ilyobius species and this record of I. nubilus from São Paulo State coast, it is possible that the I. nubilus holotype was collected from São Paulo municipality, as also discussed by Liu et al. (2015b).
Ilyobius nubilus is member of the I. chilensis group by sharing a dark pronotum and female genitalia with the gonapophysis 8 as a single, straight, sclerotized plate and the gonocoxites 8 reduced (Liu et al. 2015a). The male sternite 9 has an elongate median protrusion, which also corroborates its inclusion in this species group.
Ilyobius nubilus is closely related to I. hauseri by having similar color patter on head and pronotum, and by the forewing with similar shape, which are narrow with distinctly dilated costal area (Liu et al. 2015b). The morphological similarity in male genitalia of both species also corroborate this relationship: the male genitalia of I. hauseri and I. nubilus share sternite 9 trifurcate, with central projection longer than the lateral ones; gonocoxites 9, in lateral view, broad with rounded margins, and ectoprocts with basal margin fused to gonocoxites 11, which is Lshaped in lateral view (Mendes et al. 2022). However, both species may be differentiated as follows: in I. nubilus, the black longitudinal band on the head is wider, occupying most of the dorsal region, while in I. hauseri it is narrower and does not extend much beyond the epicranial suture (Contreras-Ramos 2008; Liu et al. 2015b). In I. nubilus, the male genitalia has the tergite 9 subrectangular, the gonocoxites 9 with a concavity on distal margin, and the gonostyli 11, in lateral view, distally projecting upwards (Fig. 7A), while I. hauseri has the tergite 9 subtriangular, the gonocoxites 9 without concavity, and the gonostyli 11, in lateral view, distally projecting downwards (Mendes et al. 2022). Female I. nubilus genitalia have the gonapophyses 8 posteriorly broadened, with a broad, arcuate, posterior notch, while in I. hauseri the gonapophyses 8 is distally convex and without any posterior notch.
The larvae of I. nubilus and I. chilensis are similar by having a subquadrate head, as wide as long, and a by sharing a pattern of digitiform marks on head, posteriorly (Archangelsky et al. 2017). However, in I. nubilus, digitiform marks are dark on light background (Fig. 9C), while in I. hauseri it is light on dark background.
description: Published as part of Mendes, Gabriela Caroline, Nascimento, Jeane Marcelle Cavalcante Do, Fusari, Lívia Maria & Hamada, Neusa, 2024, Updates on the taxonomy of Ilyobius nubilus (Navás, 1933) (Megaloptera: Sialidae: Sialinae) and Ilyobius brasiliensis (Navás, 1936) from southeastern Brazil, pp. 123-140 in Zootaxa 5406 (1) on pages 126-138, DOI: 10.11646/zootaxa.5406.1.6, http://zenodo.org/record/10611440