Barretthydrus Lea, 1927

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), The Coleopterists Bulletin 72 (4), pp. 639-661 : 641-645

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.

Figures

Figs. 1–2. Barretthydrus tibialis, instar I, head capsule. 1) Dorsal aspect; 2) Ventral aspect. EB = egg bursters: FR = frontoclypeus; PA = parietale; TP = tentorial pits. Numbers and lowercase letters refer to primary setae and pores, respectively. Color pattern not represented. Scale bar = 0.10 mm.

Figs. 3–7. Barretthydrus tibialis, instar I, head appendages. Antenna: 3) Dorsal aspect; 4) Ventral aspect. Labium: 5) Dorsal aspect; 6) Ventral aspect. 7) mandible, dorsal aspect. Numbers and lowercase letters refer to primary setae and pores, respectively. Scale bar = 0.10 mm.

Figs. 8–9. Barretthydrus tibialis, instar I, mesothoracic leg. 8) Anterior surface; 9) Posterior surface; CO = coxa; FE = femur; TA = tarsus; TI = tibia; TR = trochanter. Numbers and lowercase letters refer to primary setae and pores, respectively. Scale bar = 0.10 mm.

Figs. 10–14. Barretthydrus tibialis. Instar I: 10) Abdominal segment VIII (AB), dorsal aspect; 11) Abdominal segment VIII, ventral aspect; 12) Urogomphus, dorsal aspect. Instar III, maxilla: 13) Dorsal aspect; 14) Ventral aspect. Numbers and lowercase letters refer to primary setae and pores, respectively. Scale bars = 0.10 mm.

Figs. 15–16. Barretthydrus species, instar III, dorsal surface of head capsule. 15) B. geminatus; 16) B. tibialis. Scale bars = 0.10 mm.

Figs. 17–19. Barretthydrus tibialis, instar III. Metathoracic leg: 17) Anterior surface; 18) Posterior surface. 19) Last abdominal segment, dorsal surface. Scale bars = 0.10 mm.