Barretthydrus tibialis 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 : 645

Barretthydrus tibialis Lea, 1927

( Figs. 1–14 , 16–19 )

Source of Material. Larvae were collected in association with adults at the following localities: Australia, New South Wales, 20 km North of Nelligan, 15-VIII.1997, coll. C. H. S. Watts; Sardine Creek, 30 km North of Orbost V, 30-XI-1998, C. H. S. Watts leg.

Diagnostic Combination (Instar III). The third instar of B. tibialis can easily be distinguished from that of the closely similar B. geminatus by the presence of a broad, blackish macula on the anterior portion of the frontoclypeus ( Fig. 16 ) in addition to a relatively shorter head capsule compared to the length of abdominal segment VIII (HL/LAS <4.50 compared to>4.60) and a larger total number of secondary setae on selected leg articles ( Table 3 ).

Instar I

( Figs. 1–12 )

Description. Color: [Not available owing to the bad state of preservation of the only specimen available.] Body: Measurements and ratios that characterize the body shape in Table 1 . Head: Head capsule as in Figs. 1–2 , HL = 0.60 mm, HL/LAS = 4.61. Abdomen: As in Figs. 10–11 , U 1 = 0.75 mm; U1/HW = 1.55.

Instar II

No specimen available for study.

Instar III

( Figs. 13–14 , 16–19 )

Description. Color: Head capsule predominantly yellow; frontoclypeus with a broad, black, subapical macula ( Fig. 16 ); head appendages dark yellow; thoracic tergites dark brown; abdominal tergites I, IV – VII dark brown, II and III dark yellow to pale brown and VIII pale yellow; urogomphi dark yellow to pale brown; legs dark brown proximally, pale yellow distally. Body: Measurements and ratios that characterize the body shape in Table 1 . Head: Head capsule as in Fig. 16 , HL = 1.24–1.30, HL/LAS <4.50. Abdomen: U1 = 1.51–1.69 mm, U1/HW = 1.56–1.67 ( Fig. 19 ). Chaetotaxy: ProFE with more than 52 secondary setae; mesoFE with more than 56 secondary setae; mesoTI with more than 47 secondary setae; mesoTA with more than 34 secondary setae; metaCO with more than 26 secondary setae; metaFE with more than 66 secondary setae; metaTI with more than 50 secondary setae; metaTA with more than 43 secondary setae.

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.