Barretthydrus Lea 1927
Creators: name: Alarie, Yves
name: Michat, Mariano C.
name: Hendrich, Lars
name: Watts, Chris H. S.
Publisher: name: Zenodo
Year: 2018
Subjects: Biodiversity
Taxonomy
Animalia
Arthropoda
Insecta
Coleoptera
Dytiscidae
Barretthydrus

description: Barretthydrus Lea, 1927
(Figs. 1–19)
Diagnosis. Instar III of Barretthydrus can be distinguished from those of other genera of Australian Hydroporini that have been well studied (i.e., Antiporus and Paroster) by the following combination of characters: HL = 1.24–1.36 mm; HL/HW <1.40; nasale broad, subtriangular, not spatulate apically (Figs. 1, 15–16); parietals constricted at level of occipital suture (Figs. 15–16); primary seta FR7 hair-like (Fig. 1); A4/A3>0.30; labial palpus composed of two palpomeres (Figs. 5–6); prementum lacking spinulae along lateral margins (Figs. 5–6); L3/HW <3.50; primary seta FE7 present (Fig. 8); natatory setae present on dorsal margin of femora, tibiae, and tarsi (Fig. 18); U1/ U2’ <3.50; U1/HW <1.70.
Instar I
(Figs. 1–12)
Description. Body: Subcylindrical, narrowing towards abdominal apex. Measurements and ratios that characterize the body shape are shown in Table 1. Head: Head capsule (Figs. 1–2) pearshaped, tapering posteriorly, not constricted at level of occipital suture; ecdysial suture welldeveloped, coronal suture short; frontoclypeus elongate, bluntly rounded, subtriangular with welldeveloped lateral branches, anteroventral margin with 12 ventral lamellae clypeales (Bertrand 1972); dorsal surface with 2 spine-like egg bursters (ruptor ovi of Bertrand 1972) at about mid-length; ocularium present, stemmata not visible ventrally and subdivided into 2 vertical series; epicranial plates meeting ventrally; tentorial pits visible medioventrally at about mid-length. Antenna (Figs. 3–4) elongate, slightly shorter than HW; composed of 4 antennomeres, A2 and A3 longest, A1 shortest; A3’ relatively elongate, shorter than A4; A3 lacking ventroapical spinula. Mandible (Fig. 7) prominent, falciform, distal half projecting inwards and upwards, apex sharp; mandibular channel present. Labium (Figs. 5–6), prementum subrectangular, about as long as broad, lacking lateral marginal spinulae; LP elongate, distinctly shorter than MP, composed of 2 palpomeres; LP2 subfusiform, distinctly longer than LP1. Maxilla (Figs. 13–14) with short, thick stipes, incompletely sclerotized ventrally; cardo fused to stipes; galea and lacinia absent; MP elongate, slightly shorter than antenna, composed of 3 palpomeres; MP1 and MP2 longest, MP2 distinctly longer than MP1. Thorax: Thoracic terga convex, pronotum slightly shorter than meso- and metanota combined, meso- and metanota subequal; protergite subrectangular to subovate, more developed than meso- and metatergites; [We were unable to determine the presence of an anterotransverse carina owing to the bad condition of the only specimen available.]; thoracic sterna membranous; spiracles absent. Legs: Long (Figs. 8–9), composed of 6 articles (sensu Lawrence 1991); L1 shortest, L3 longest; CO robust, elongate, TR divided into 2 parts by an annulus, FE, TI, and TA slender, subcylindrical, PTwith 2 long, slender, slightly curved claws; posterior claw shorter than anterior claw on L1 and L2, posterior claw longer than anterior claw on L3; femora, tibiae, and tarsi lacking spinulae along ventral margin. Abdomen: Eight-segmented (Figs 10–11); segments I–VI sclerotized dorsally, membranous ventrally; segment VII sclerotized both dorsally and ventrally, ventral sclerite independent from dorsal one; tergites I–VII narrow, transverse, rounded laterally, lacking sagittal line; [We were unable to determine the presence of an anterotransverse carina owing to the bad condition of the only specimen available.]; segment VIII (=LAS) longest, completely sclerotized, ring-like, strongly constricted at point of insertion of urogomphus; projecting backwards into a very short, subconical siphon; spiracles absent lateroventrally on segments I–VII. Urogomphus very long, composed of 2 urogomphomeres; U1 long, much longer than segment VIII; U2 narrower, setiform, much shorter than U1. Chaetotaxy: Similar to that of generalized Hydroporinae larva (Alarie and Harper 1990; Alarie et al. 1990; Alarie 1991; Alarie and Michat 2007 a) except for the following features (Figs. 1–12): Pores PAd and ANf absent; pore ANh distal; setae MX 4 and TR2 absent; pore FEa articulated distally, close to seta FE5; seta TI7 short, spine-like; seta AB10 spine-like; setae UR2 and UR3 contiguous, seta UR4 articulated posteriorly; setae UR5, UR6, and UR7 elongate; seta UR8 inserted subapically. [Pore PAk and seta PA13 could not be located. We are reluctant to consider them as lacking due to the condition of the only instar I specimen available.]
Instar II
No specimens were available for study.
Instar III
(Figs. 13–19)
Description. As instar I except as follows: Body: Measurements and ratios that characterize the body shape in Tables 1 and 2. Head: Head capsule (Figs. 15–16) constricted at level of occipital suture; egg bursters lacking. Antenna elongate, distinctly shorter than HW. LP2 subequal to slightly shorter than LP1. MP subequal in length to antenna, MP1 slightly shorter than MP2 (Figs. 13–14). Thorax: Protergum lacking anterotransverse carina; both meso- and metathoracic terga with an anterotransverse carinae; sagittal line visible; mesopleural region with a spiracular opening on each side. Legs: Position and number of secondary setae in Table 3; natatory setae present on dorsal margin of femora, tibiae, and tarsi (Figs. 17–18). Abdomen: Segment VII completely sclerotized both dorsally and ventrally, all tergites with anterotransverse carina (Fig. 19); mesopleural region of segments I–VII with a spiracular opening on each side. Chaetotaxy: Head capsule with numerous secondary setae; lateroventral margin of PA with several secondary spine-like setae (Figs. 15–16); anteroventral margin of nasale with half circle of about 60 lamellae clypeales of different lengths, directed downwards; AN, MX, and LA lacking secondary setae; MN with 1 hair-like secondary seta on basoexternal margin; thoracic and abdominal sclerites I–VIII with numerous secondary setae mainly on posterior half; natatory setae present on dorsal margin of femora, tibiae, and tarsi; secondary leg setation in Tables 3-4 and Figs. 17–18; U with secondary setae (Fig. 19).
Remarks. Larvae of Barrethydrus can readily be distinguished from those of other Australian Hydroporini described in detail (i.e., Paroster and Antiporus) by the presence of natatory setae on the dorsal margins of the femur, tibia, and tarsi and metric characters presented in Table 2, and, superficially, from the less well-studied genera by the strong, dark yellow banding on the body.
Distribution. Endemic to Australia.
description: Published as part of Alarie, Yves, Michat, Mariano C., Hendrich, Lars & Watts, Chris H. S., 2018, Larval Description and Phylogenetic Placement of the Australian Endemic Genus Barretthydrus Lea, 1927 (Coleoptera: Dytiscidae: Hydroporinae: Hydroporini: Sternopriscina), pp. 639-661 in The Coleopterists Bulletin 72 (4) on pages 641-645, DOI: 10.1649/0010-065X-72.4.639, http://zenodo.org/record/4789513