Gyrinus (Neogyrinus) rozei Ochs, 1953: 186 [original description]

Material examined. Brazil, Roraima state, Boa Vista county, Fazenda Agrolucas, lago artificial, ‘02°52’29.7’S, 60°51’48.9’O, 12/vii/16, Col. N. Hamada, J.M.C. Nascimento, D. Colpani [10♂ 10♀ adults, 2 larvae, 145 pupae, INPA]; Serra da Lua, Boa Vista county, artificial lake, ‘02°14’57.40’S, 60°44’59.76’O, 14/vii/16, Col. N. Hamada, J.M.C. Nascimento, D. Colpani [5♂ 2♀ adults, 1 larva, 8 pupae, INPA].

Adult. A detailed description of adult stage is given by Gustafson & Short (2017).

Egg. (Figs 4–10, Table 2)

Description. Long, cylindrical, length 1.10–1.24 mm, width 0.26–0.30 mm (n = 10), color varying from cream to testaceous (just before eclosion) (Figs 4–6). As the embryo develops, the longitudinal fissure expands laterally along the egg (Fig. 5). Under SEM (Figs 7–10), the dorsal surface of the chorion is sculptured in dorsal view and smooth in ventral view. The reticulation on the dorsal surface of chorion is alveolate (Harris, 1979), the cells are 30.4–39.6 µm long, 15.0–19.0 µm wide. In each cell, we observed circular shaped superficial grooves randomly distributed (Figs 9–10). The micropyle projection is short, wider (1.9–2.0 µm) than long (1.3–1.5 µm), with apex truncated. The micropyle is located on the anterior pole (Fig. 8).

Comparative notes. Newly laid eggs are cream-colored and loosely fixed to the substrate by a mucous-like substance. The general structure of the eggs of G. rozei (length, width, shape, color, presence of sculpture on the chorion, longitudinal splitting-slit and micropylar projection) is congruent with that previously described for the family (Saxod 1964; Baker & Wai 1987; Komatsu & Kobayashi 2012; Colpani et al. 2018).

There are few descriptions of Gyrinidae eggs in the literature, especially based on SEM and transmission electron microscopy (Baker & Wai 1987; Komatsu & Kobayashi 2012; Colpani et al. 2018). Comparing the morphology of the eggs of G. rozei and those of other genera, several differences arise (Table 2). In Dineutus, the chorionic sculpture is well differentiated compared to that of Gyretes and Gyrinus. For example, in D. hornii and D. mellyi the chorionic sculpture is formed by conical projections covering the entire surface of the egg and the apex of the micropyle is irregular, differing from Gyretes and Gyrinus in which the sculpture of the chorion forms cells that are similar to a honeycomb and the apex of the micropyle is truncated, rounded or pointed (Table 2) (Baker & Wai 1987; Komatsu & Kobayashi 2012; Colpani et al. 2018). Eggs of Gyrinus rozei may be distinguished from those of Gyrinus substriatus Stephens, 1829 by the chorion reticulation shape, which is alveolate in the former and hexagonalshaped in the latter (Sadox 1964). The same structure distinguishes the eggs of G. rozei from those of some Gyretes species. For instance, in Gyretes nubilus Ochs, 1965 the chorion reticulation varies from rounded to quadrangular, while in Gyretes minax Ochs, 1967 it may be triangular, rounded, cylindrical or rectangular (Table 2). The apex of the micropyle is truncated in G. rozei, pointed in Gyretes nubilus, and rounded in Gyretes minax (Table 2). Gyrinus rozei differs from G. substriatus and other genera such as Dineutus and Gyretes in having superficial, circular shaped grooves in each chorion cell, while in the other species the chorion cells have a smooth surface (Table 2).

Larvae (Figs 11–26, Table 3)

Diagnosis. Larvae of G. rozei are characterized by the following features: cephalic capsule not constricted at occipital region (instars I–III); medial lobe of frontoclypeus with two conspicuous teeth (instars I–III); stipes with five robust hook-like additional setae of different sizes on dorsointernal margin (instars I–III); lacinia hook-shaped (instars I–III); mandible with additional short spine-like setae in dorsolateral portion (instar I); protibial seta TI1 spine-like (instars I–III); ventral surface of profemur and protibia with several short spine-like secondary setae (instar III).

Description. First-instar larva (Fig. 11). Color. Body with scarce pigmentation, cephalic capsule, mandible, pronotum, legs and terminal hooks testaceous, meso- and metathorax and abdomen white.

Body. Elongate, parallel-sided, head and pronotum sclerotized, rest of thorax and abdomen soft. Head about 1.3 times longer than pronotum. Measurements and ratios are shown in Table 3.

Head (Fig. 14). About 1.3 times longer and 1.2 wider than pronotum; longer than broad; not constricted at level of occipital region; posterior margin concave; occipital suture absent; coronal suture short; frontal sutures V-shaped, extending to antennal bases. Frontoclypeus elongate, anterior margin with three well delimited lobes; medial lobe well developed, with two teeth on anterior margin; lateral lobes well developed, truncated. Stemmata present, forming a cluster where each stemma could not be individualized (Fig. 14). Egg bursters present dorsally, formed by four small cuticular spines on each posterolateral surface of parietal.

Antenna (Figs 16, 17): Long, slender; A1 shortest, A2 and A3 3.0 times the length of A1, A4 longest and nar- rowest. A3 with one-minute spinula on ventrodistal surface, and two subapical flat plates on inner margin, distal one interpreted as the sensorium (A3’) which does not protrude; A4 with a subapical flat sensorial plate on inner margin, accompanied by two minute structures (probably spinulae or pores).

Maxilla (Figs 18, 19): Short, robust, cardo strongly developed, subquadrate, bearing a group of minute spinulae on dorsal surface; stipes short, broad, subtrapezoidal, with a lacinia and galea on distal inner margin and a palpifer on distal outer margin; lacinia well developed, wide, roughly hook-shaped, indented apically; galea with two articles, first article short, globose, second article somewhat shorter, narrow (Figs 18, 19). Palpifer short, projected apicodorsally in a subtriangular process; palpus composed of three articles, MP1 of about same length as MP2, MP3 1.6 times longer than MP1 and MP2 (Figs 18, 19).

Labium (Figs 20, 21): Well developed, prementum divided longitudinally into two halves fused basally, each half bearing minute spinulae on dorsal surface. LP1 of about same length as LP2.

Mandible (Fig. 22): Mandibles symmetrical, elongate, curved, distal half projected inward, apex sharp; inner margin more or less toothed on distal third; mandibular channel present.

Thorax (Fig. 11): Long, narrow, pronotum narrower than head, mesonotum and metanotum subequal in length; protergite with anterior and posterior margins truncate, lateral margins rounded; spiracles absent.

Legs (Figs 23, 24): Long, slender, coxa longest, 2.8 times longer than trochanter, trochanter shortest, profemur 1.2 times longer than protibia, protibia 1.3 times longer than protarsus, pretarsus with two slightly curved claws subequal in length.

Abdomen (Fig. 11): Ten-segmented, long, narrow, subcylindrical, segments I–V of similar width, segments VI–X progressively narrowing towards the apex. Segments I–VIII with a pair of thickly plumose tracheal gills at posterolateral angles, segment IX narrower, with two pairs of tracheal gills at posterolateral angles; segment X narrowest, with four strongly sclerotized terminal hooks, medial hooks much shorter than lateral hooks (Figs 25, 26).

Chaetotaxy. Similar to that of G. monrosi Mouchamps, 1957 (Michat et al. 2010) except that the row of robust hook-like additional setae on dorsointernal margin of stipes is composed of five setae (Figs 18, 19).

Description. Second-instar larva . Similar to first instar except for the following features: Color (Fig. 12). Cephalic capsule yellowish, cephalic capsule and pronotum well sclerotized, abdominal segments darker.

Body (Fig. 12). Length 7.00–9.00 mm, width 0.40–0.70 mm; head a little narrower and about 1.2 times longer than pronotum. Measurements and ratios in Table 3.

Head (Fig. 12). Coronal suture 0.5 times length of frontal sutures. Stemmata well differentiated, four dorsal and two ventral. Egg bursters absent.

Chaetotaxy. Cephalic capsule with numerous secondary setae, cardo, stipes and palpifer with short secondary spine-like setae. Dorsal and ventral surfaces of abdominal segment IX with several short spine-like setae.

Description. Third-instar larva. As second-instar except for the following features: Color (Fig. 13). Pronotum darker compared to head, with light brown and dark spots. Mesonotum, metanotum and abdominal segments I–V darker, color of segments VII–X from white to beige, lighter compared to other abdominal segments, light brown maculae covering the abdominal segments. Legs testaceous.

Body (Fig. 13). Length 9.12–9.54 mm, width 1.20–1.31 mm; pronotum about 1.5 times longer and 1.4 times wider than head. Measurements in Table 3.

Abdomen (Fig. 13). Spiracles present on dorsolateral margin of segments I–III.

Chaetotaxy. Basal half of external margin of mandible with several short spine-like secondary setae. Ventral surface of protarsus with several short spine-like secondary setae.

Comparative notes. According to Crespo (1989a), members of G. (Oreogyrinus) and G. (Neogyrinus) differ in some characters, for example members of G. (Oreogyrinus) possess the medial hooks of the abdominal segment X slightly longer than the lateral hooks, whereas in G. (Neogyrinus) (Crespo 1989b) the medial hooks are much shorter than the lateral hooks. The number of hook-like setae on the dorsointernal margin of the stipes also varies between larvae of the G. (Neogyrinus) (0−5 setae) (Crespo 1989b) and G. (Oreogyrinus) (6 setae) (Michat et al. 2010). In G. (Neogyrinus) rozei we observed five robust hook-like setae, similar to G. (Neogyrinus) ovatus. The medial hooks are also much shorter than the lateral hooks in G. (Neogyrinus) rozei, similar to G. (Neogyrinus) ovatus, further supporting the utility of this character to distinguish subgenera.

The first-instar larva of Gyrinus (Neogyrinus) rozei differs from that of G. (Oreogyrinus) monrosi in having only one ventral spinula on third antennomere, while G. (Oreogyrinus) monrosi has two ventral spinulae. Also, G. monrosi bears a group of small spinulae dorsally at base of palpifer (absent in G. rozei). The third-instar larva of G. (Neogyrinus) rozei differs from that of G. (Oreogyrinus) monrosi in having 10−20 secondary setae on the external margin of the mandible, while G. (Oreogyrinus) monrosi has only four minute secondary setae.

Larvae of these two species also differ in the number and position of additional setae in the cephalic capsule and in the size of the hooks of abdominal segment X. On the other hand, the number of cuticular spines forming the egg bursters also varies among species, being four in G. (Neogyrinus) rozei and three in G. (Oreogyrinus) monrosi, whereas in the dineutine genera Dineutus, Enhydrus Laporte, 1834 and Macrogyrus (Andogyrus) Ochs, 1924 the egg bursters are formed by a single cuticular spine (Archangelsky & Michat 2007; Michat et al. 2010, 2016; Michat & Gustafson 2016; Michat et al. 2017).

Larvae of Gyrinus and Gyretes differ from those of the dineutine genera in having the pore MXg distally located (proximally located in Dineutini) and in the presence of seta TR2 (absent in Dineutini). On the other hand, Gyrinus differs from Gyretes and the Dineutini genera in the presence of an additional pore on the trochanter (absent in the other genera) and in the hair-like condition and distal position of seta TA1 (spine-like and more proximally inserted in the other genera) (Archangelsky & Michat 2007; Michat et al. 2010, 2016; Michat & Gustafson 2016; Michat et al. 2017; Colpani et al. 2018).

Pupa (Figs 27, 28, Table 4)

Description. Color (Figs 27, 28, Table 4): Yellowish to light-white in dorsal and ventral view. Eyes black.

Body (Fig. 27, Table 4). Completely membranous. Dorsal side with short setae, ventral side glabrous, with all appendages well developed. Head strongly inclined, well developed, not visible from above; compound eyes large, completely divided into upper and lower portion. Antenna short. Clypeus and labrum well developed. Pronotum with a pair of longitudinal rows of setae close to median line, divided in two groups: one medially located (central group), and another one laterally located. Mesothorax with distinct groups of setae on medial area. Metathoracic setae with rather irregular pattern, arranged laterally. Abdomen with eight fully developed segments, abdominal tergites I–VII with rather irregular transverse rows of setae. The number and position of dorsal setae are presented in Table 4. Wing sheaths partly visible from above, sheaths of hind wings almost contiguous ventromedially. Leg sheaths only visible in ventral view. Sheaths of prolegs overlapped with those of middle legs. Sheets of hind legs completely covered by those of middle legs. Stigmata I–VIII present, reduced and indistinct. Cerci absent. Gonopodes present at caudal end of abdomen.

Comparative notes. The pupae of G. (Neogyrinus) rozei is similar to that of G. (Oreogyrinus) argentinus Steinheil, 1869 (Crespo 1989a) in several features, in particular the distribution pattern and number of dorsal setae on the pronotum, mesothorax, metathorax and abdominal terga. The description of the pupae of Macrogyrus (Andogyrus) seriatopunctatus (Régimbart, 1882) in Bachmann (1961) provides little information. However, from our observa- tions, the general color in M. (A.) seriatopunctatus is yellowish green, differing from yellowish to light-white in G. (Neogyrinus) rozei.