Gyretes nubilus Ochs, 1965

Colpani, Daniara, Benetti, César João, Hamada, Neusa, Andrade-Souza, Vanderly & Michat, Mariano C., 2018, Gyretes Brullé (Coleoptera: Gyrinidae) from Brazil: Morphology of eggs and early instars, Zootaxa 4526 (3), pp. 331-346 : 335-342

Gyretes nubilus Ochs, 1965

(Figs. 10–24)

Diagnosis. Larvae of Gyretes can be distinguished from those of other described Gyrinidae genera by the following combination of characteristics: cephalic capsule not constricted at the level of the occipital region (slightly constricted in instar II) (Figs. 12–13, 24); occipital suture absent (Figs. 12, 24); anterior margin of frontoclypeus lacking teeth (Figs. 12, 24); seta FR3 short, hair-like (Fig. 12); parietal with three additional setae on lateral region, contiguous to stemmata (Fig. 12); lacinia not serrate on posterior margin, not indented apically (Figs. 16–17); last maxillary palpomere in dorsal view with six pore-like additional structures near apex (Fig. 16), in ventral view with one additional seta on distal portion (Fig. 17); pore MXg proximal (Fig. 17); cardo and stipes each with one additional seta on ventral region (Fig. 17); maxillary and labial palpomeres without additional pores (Figs. 16–19); pore LAc located medially (Fig. 18); mandible with six spines on inner margin and several additional setae on dorsal surface (Fig. 20); seta CO12 proximal (Fig. 22); coxa lacking additional setae (Figs. 21–22); setae FE2, FE3 and TI3 bifid (Fig. 21); seta TR2 present (Fig. 21); claws lacking basoventral spinulae (Figs. 21–22); abdominal segment X lacking ventral spinulae (Fig. 23); tracheal gills bearing long spinulae.

Description. First instar larva. Color (Figs. 10–11): Cephalic capsule with an irregular brown spot that extends from basal region of coronal suture to of frontal sutures, and one brown macula on each laterobasal angle. Antenna, maxilla, and labium white to light brown. Thoracic sclerites light brown, meso- and metathorax whitish with light brown spots arranged at random. Legs and abdominal segments testaceous, terminal hooks brown.

Body. (Fig. 10): Elongate, head and pronotum strongly sclerotized, rest of body weakly sclerotized. Measurements and ratios are presented in Table 2.

Head. Cephalic capsule (Figs. 10–13): Subrectangular, 1.7 times longer than pronotum, parallel sided, coronal suture short; frontal sutures V-shaped, extending to antennal bases (Fig.12). Frontoclypeus subtriangular, with anterior margin straight (without teeth) and anterior corners rounded (Fig. 12). Stemmata present, forming a cluster where each stemma could not be individualized (Fig. 11). Egg bursters present, formed by a single cuticular spine on each posterolateral surface (Fig. 12).

Antenna (Figs.14–15): Long, slender, composed of four articles, first antennomere shortest, second and third antennomeres 3.0 times more elongated in relation the first, fourth antennomere longest in relation to the other antennomeres, narrowed at base and at apex. Third antennomere with two minute spinulae on ventrodistal surface, and two subapical flat plates on inner margin. Fourth antennomere with a subapical flat sensorial plate on distal inner margin, accompanied by one spinula.

Maxilla (Figs. 16–17): Long, slender, cardo subrectangular, stipes subglobular, broad, about as long as cardo. Lacinia slender, slightly curved, apically tapered. Galea with two articles, first galeomere short, globose, second galeomere longer, narrowing to apex. Palpifer short, subrectangular, maxillary palpus composed of three articles, first palpomere 3.5 times longer than palpifer, second palpomere shorter than third palpomere (0.07–0.08 mm), third palpomere longest, curved and slightly widened.

Labium (Figs. 18–19): Well developed, prementum longitudinally subdivided in two halves, first palpomere 1.4 times longer than second palpomere, second palpomere curved, narrow at base and widened towards the apex.

Mandible (Fig. 20): Mandibles of both sides symmetrical, elongate, robust, curved, broadest in basal region, apex sharp, inner margin with six small spines on central portion, mandibular channel present.

Thorax (Fig. 10): Long, narrow, pronotum with about same width as head, mesonotum and metanotum subequal in length. Protergite well developed, membrane between pronotum and mesonotum with single narrow transverse sclerite, both sclerites with sagittal line; spiracles absent.

Legs (Figs. 21–22): Long, slender, longest coxa 1.4 times longer than trocanther, trocanther shortest, profemur, protibia and protarsus slender, profemur (1.5 times) longer than protibia, and protibia 1.4 times longer than protarsus, preprotarsus with two slightly curved claws subequal in length.

Abdomen (Fig. 10): Long, narrow, with 10 segments, subcylindrical, segments I–V of similar width, segments VI–X progressively narrowing towards the apex. Segments I-VIII with a pair of lateral tracheal gills at posterior angles, segment IX narrower, with two pairs of tracheal gills at posterior angles; segment X narrowest, with four strongly sclerotized terminal hooks (Figs. 10, 23).

Chaetotaxy. Frontoclypeus (Fig. 12): Medial region of anterior margin with two spine-like setae (FR10, FR11). Anterior (submarginal) region with three short hair-like setae (FR5, FR7, FR8), two minute setae (FR6, FR9) and one pore (FRe). Central portion with one short hair-like seta (FR4). Lateral margin with two short hairlike setae (FR1, FR2) and two pores (FRa, FRc) on distal third, and one hair-like seta (FR3) at base.

Parietal (Figs. 12–13): Dorsal surface (Fig. 12) with one short hair-like seta (PA10) near antennal base, three conspicuous additional setae external to stemmata, four short and two elongate setae (PA4, PA5, PA6, PA7, PA8, PA9) posterior to stemmata, and three short spine-like setae (PA1, PA2, PA3) and two pores (PAa, PAb) near posterior margin. Ventral surface (Fig. 13) with two short hair-like setae (PA18, PA19) and one pore (PAo) near anterior margin; two short hair-like setae (PA11, PA12) and four pores (PAf, PAg, PAh, PAi) on anterolateral angle; two short hair-like setae (PA16, PA17) on central portion, two short hair-like setae (PA13, PA14) and one pore (PAk) near lateral margin at about mid length, and one relatively elongate hair-like seta (PA15) and one pore (PAm) on basal third. Some inconspicuous additional setae present on dorsal and to a lesser extent ventral surface.

Antenna (Figs. 14–15): First antennomere with three pores (ANa, ANb, ANc) on dorsodistal portion and two pores (ANd, ANe) on ventrodistal portion. Second antennomere with one pore (ANi) on ventromedial portion. Third antennomere with one pore (ANf) on dorsomedial region and two short hair-like setae on distal portion. Fourth antennomere with two short spine-like setae (AN4, AN5) and one pore (ANg) at apex.

Maxilla (Figs. 16–17): Cardo with one short hair-like seta ( MX 1) and one short additional seta on ventral surface. Stipes with one hair-like seta ( MX 3) on laterodorsal region, one short hair-like seta ( MX 2), one very short hair-like seta ( MX 4), one short additional seta and two pores (MXa, MXb) on ventral surface, and two spine-like setae ( MX 5, MX 6) at base of lacinia. First galeomere with one short hair-like seta ( MX 7) on ventral margin. Second galeomere with two pores (MXd, MXh) on ventral surface, one spine-like seta ( MX 8) on dorsal surface, and one short hair-like seta ( MX 9) at apex. Palpifer with one short hair-like seta ( MX 10) on ventral surface. First palpomere with one pore (MXf) on dorsodistal portion and one minute seta ( MX 13) and one pore (MXe) on ventroproximal portion. Second palpomere with one short hair-like seta ( MX 11) on dorsodistal portion, one short hair-like seta ( MX 12) on ventrodistal portion, and one pore (MXg) on ventroproximal portion. Third palpomere with one pore (MXj) on dorsomedial portion, one short hair-like seta ( MX 14) and one short additional seta on ventrodistal portion, and a longitudinal row of four minute pore-like additional structures on dorsodistal portion.

Labium (Figs. 18–19): Prementum with three short hair-like setae (LA3, LA4, LA5) and one pore (LAa) near anterior margin, one minute spine-like seta (LA9) on ventrodistal surface, one short hair-like seta (LA2) on ventrodistal portion, and one minute seta (LA1) on ventroproximal surface. First palpomere with one pore (LAb) on ventroproximal portion. Second palpomere with one short hair-like setae (LA12) ventrally close to apex and one pore (LAc) on dorsomedial portion.

Mandible (Fig. 20): Dorsal surface with one pore (MNa) on proximal portion, two hair-like setae (MN1, MN2) and two pores (MNb, MNc) on distal portion, and numerous minute additional setae.

Legs (Figs. 21–22): Anterior surface of coxa with six short spine-like setae (CO1, CO2, CO3, CO4, CO5, CO17) and one short hair-like seta (CO18) on proximal portion, one short hair-like seta (CO7), three relatively more elongate hair-like setae (CO6, CO8, CO9) and one pore (COa) on central portion, and one short hair-like seta (CO10) on distal portion. Posterior surface of coxa with four short spine-like setae (CO13, CO14, CO15, CO16) on proximal portion, one short hair-like seta (CO12) and one pore (COd) on central portion, and one short spine-like seta (CO11) on distal portion. Anterior surface of trochanter with two short hair-like setae (TR1, TR2), two relatively more elongate hair-like setae (TR3, TR4), and five pores (TRa, TRb, TRc, TRd, TRe). Posterior surface of trochanter with three short hair-like setae (TR5, TR6, TR7) and two pores (TRf, TRg). Anterior surface of profemur with one hair-like seta (FE1) and one pore (FEb) on proximal portion, and two short spine-like setae (FE2, FE3) on distal portion. Posterior surface of profemur with one short spine-like seta (FE4) on central portion and two short spine-like setae (FE5, FE6) on distal portion. Anterior surface of protibia with one long hair-like seta (TI1) on proximal portion and three short spine-like setae (TI2, TI3, TI4) on distal portion. Posterior surface of protibia with one pore (TIa) on central portion and one long hair-like seta (TI7) and two short spine-like setae (TI5, TI6) on distal portion. Anterior surface of protarsus with one pore (TAa) on central portion, and three short spinelike setae (TA2, TA3, TA4), one minute seta (TA7) and two pores (TAc, TAd) on distal portion. Posterior surface of protarsus with one short spine-like seta (TA1) on central portion, and two short spine-like setae (TA5, TA6) and three pores (TAb, TAe, TAf) on distal portion. Anterior surface of preprotarsus with one relatively elongate spinelike seta (PT1) on basoventral portion. Posterior surface of preprotarsus with one short spine-like seta (PT2) on basoventral portion.

Abdomen (Fig. 23): Segments I–IX with short hair-like setae on dorsal and ventral surfaces. Segment X: dorsal surface with two short spine-like setae; ventral surface with four setae; lateromedial portion with two pores; laterodistal portion with one seta and one pore. Terminal hooks with two pores on ventral margin at about midlength (Fig. 23).

FIGURES. 2–9. Eggs of Gyretes analyzed under scanning electron microscopy. Gyretes nubilus : (2) Dorsal view, (3) Micropyle (anterior pole), (4) Lateral region amplified showing chorion details, (5) Lateral view of micropyle. Gyretes minax : (6) Dorsal view, (7) Micropyle (anterior pole), (8) Lateral region amplified showing chorion details, (9) lateral view of micropyle.

FIGURES. 10–11. Gyretes nubilus , first-instar larva. (10) Habitus, dorsal view, (11) Head and pronotum, dorsal view, Scale bars 1.0 mm (Figure 10), 0.2 mm (Figure 11).

Description. Second-instar larva. Similar to first-instar larva except for the following features: Color (Fig. 11): Cephalic capsule and pronotum yellowish with light brown pigmentation, abdominal segments darker, meso- and metanotum with light brown maculae.

Body (Fig. 24): Measurements and ratios in Table 2.

Head (Fig. 24): Stemmata well differentiated, four dorsal and two ventral.

Chaetotaxy. Cephalic capsule with numerous secondary setae, which can be differentiated from the other setae by their shorter length and slender shape. Second antenomere with four small cuticular spines randomly distributed. Cardo and stipes with short secondary spine-like setae. Palpifer with cuticular spines covering all its extension. Mandible with secondary setae on dorsal surface.

FIGURES. 12–13. Gyretes nubilus , first-instar larva, cephalic capsule. (12) Dorsal view. (13) Ventral view. Numbers and lowercase letters indicate primary setae and pores. Note: frontoclypeus (FR), parietal (PA) and egg bursters (EB). Scale bar 0.5 mm. black square = Conspicuous additional setae. Inconspicuous additional setae not labeled.

FIGURES. 14–20. Gyretes nubilus , first-instar larva. (14). Right antenna, dorsal view. (15). Left antenna, ventral view. (16) Right maxilla, dorsal view. (17) Left maxilla, ventral view. (18) Labium, dorsal view (19) Labium, ventral view. (20). Right mandible, dorsal view. Numbers and lowercase letters indicate primary setae and pores. Note: antenna (AN), labium (LA), mandible (MN), maxilla ( MX). Scale bars 0.1 mm (Figs. 16, 17, 20), 0,3 mm (Figs. 14, 15, 18, 19). Black square = Additional setae (except for minute additional setae on mandible which are not labelled).

FIGURES. 21–24. Gyretes nubilus . 21–23. First-instar larva. (21) Left metathoracic leg, anterior view. (22) Right metathoracic leg, posterior view. (23) Abdominal segment X, ventral view. (24) Second-instar larva, cephalic capsule, dorsal view. Numbers and lowercase letters indicate primary setae and pores. Note: frontoclypeus (FR), parietal (PA). Scale bars 0,3 mm (Figure. 23), 0,5 mm (Figures. 21, 22, 24). Black square = Additional setae.