Redescription and neotype designation of Suphis fluviatilis Guignot, 1948 (Coleoptera: Dytiscoidea: Noteridae) and notes on other species of the genus.

Suphis fluviatilis Guignot, 1948 was described based on a single female specimen, and according to the author, the type was deposited in the Museum National dHistoire Naturelle (Paris, France). However, the diagnostic features of the specimen deposited under this name and provided with the respective labels deviate considerably from those given by Guignot in his original description. It is shown that this specimen belongs to Suphis notaticollis Zimmermann, 1921, confirming previous observations by Luis Grosso in 1980. Thus, a neotype of S. fluviatilis is designated to avoid instability of the nomenclature by the impending synonymy of S. fluviatilis with S. notaticollis. Suphis fluviatilis is redescribed in detail, including illustrations of the main diagnostic characters. The species is compared with other Neotropical Suphis species, in particular with S. notaticollis. Additionally, the male genitalia of Suphis intermedius Rgimbart, 1903 are described for the first time, and a first record from Paraguay is given.

Description and chaetotaxic analysis of the larval instars of Hydrocanthus debilis Sharp, 1882 (Coleoptera: Noteridae).

All larval instars of the burrowing water beetle species Hydrocanthus debilis Sharp, 1882 are described and illustrated, including morphometric and chaetotaxic analyses of the cephalic capsule, head appendages, legs, last abdominal segment, and urogomphus. Larvae of this species have many small dark dorsal maculae on the body, which easily distinguishes it from other known species of the genus except H. socius Sahlberg, 1884. Larvae of H. debilis can easily be separated from those of H. socius by their smaller size, the length of parietal seta PA13 relative to seta PA14, and the relative distance between egg bursters.

Chaetotaxy and morphometry of the head capsule and head appendages of the genus Derallus Sharp (Coleoptera: Hydrophilidae).

The primary and secondary chaetotaxy of the head capsule and head appendages of the three larval instars of the water scavenger beetle genus Derallus Sharp are described for the first time based on two species: D. angustus Sharp and D. paranensis Oliva. Morphometric characters derived from the head capsule and mouthparts are included, together with detailed illustrations of all characters. Chaetotaxy of these larvae is compared with that of Regimbartia attenuata (Fabricius), another species belonging to the Derallus-clade of Berosini.

Description of immatures of Berosus decolor Knisch, 1924 (Coleoptera: Hydrophilidae: Berosini), with emphasis on chaetotaxy and morphometry.

The preimaginal stages of Berosus decolor Knisch, 1924 are described for the first time, including illustrations of the egg case and all larval instars. Larval morphology of this species is studied emphasizing chaetotaxic and morphometric analyses. The egg case lacks a mast and contains 2‒3 eggs; all larval instars are characterized by the following features: presence of 6 teeth on anterior margin of nasale; left epistomal lobe carrying 14‒16 strong and curved setae (gFR2); seta FR1 elongate, inserted posteriorly to seta PA7; pore FR14 absent; parietale with spinulae in the area between setae PA5 and PA12; mandibles asymmetrical; seta MN1 minute; first antenommere with a digitiform projection on distal inner margin; antennal sensilla AN8 and AN9 absent; maxillary sensilla MX10 hair-like, MX11 and MX16 with an intermediate shape between hair-like and spine-like; labial sensilla LA4 and LA15 absent; seta LA2 present, minute; abdomen with 7 pairs of tracheal gills. The morphology of the egg cases and larvae within the genus Berosus are compared and discussed.

Description of immatures of the genus Tropisternus Solier, subgenus Pristoternus Orchymont (Coleoptera: Hydrophilidae), with emphasis on the chaetotaxy and morphometry of larval forms.

The egg cases, larvae, and pupae of Tropisternus (Pristoternus) latus (Brullé, 1837), T. (P.) ovalis Castelnau, 1840, and T. (P.) laevis (Sturm, 1826) are illustrated and described for the first time. The egg cases are built with or without a mast, which can be ribbon-like or globular; all larval instars have seven anterior denticles in the anterior margin of nasale, and the antennal seta AN8 is present; the pupae bear 6 or 8 styli on the abdominal segments II-VI, the pleural styli can be either short or very long, and horn-like projections may be present on the abdominal segments II-VI. A comparison of the morphology of the egg cases, pupae and larval chaetotaxic and morphometric characters within the genus Tropisternus is presented.