Platambus sawadai ( Kamiya, 1932 )

Okada, Ryohei, Alarie, Yves & Michat, Mariano C., 2019, Description of the larvae of four Japanese Platambus Thomson, 1859 (Coleoptera: Dytiscidae: Agabinae) with phylogenetic considerations, Zootaxa 4646 (3), pp. 401-433 : 418

Description of the larvae of Platambus sawadai ( Kamiya, 1932)

Source of material. 7 instar I, 10 instar II, 10 instar III, Japan: Happudani riv., Ishigure pass, Higashiomi-shi, Shiga Pref., 28.XI.2015; 20.XII.2015; 10.I.2016; 6.II.2016, R. Okada leg. Larvae were identified ex societate imaginis. The identification is firm since P. sawadai is the only Platambus species known at this locality.

Diagnosis. First instar larva of P. sawadai can be distinguished from the other species studied by the following combinations of features: frontoclypeus with more than 13 spatulate setae ( Fig. 43 ); seta FR3 subequal in length to seta FR2 ( Fig. 43 ); seta PA6 longer than seta PA7 ( Fig. 43 ); primary seta LA10 inserted submedially ( Fig. 50 ); ratio L3/HW = 3.10–3.30. In addition to color patterns of head capsule ( Fig. 60 ), last abdominal segment, and urogomphi ( Figs 73–82 ), the total number of spatulate setae on frontoclypeus, secondary setae on pro- and mesofemur and the presence/absence of ventral setae on protarsus ( Table 2 ) are helpful at discriminating later instars.

Instar I ( Figs 43–56 , 75 ). Color. Dorsal surface of head capsule predominantly pale yellow; frontoclypeus pale yellow anteriorly, dark grey around each egg burster; parietale pale yellow with dark V-shaped band across ecdysial suture; head appendages pale yellow; thoracic and abdominal terga I to VII dark grey; LAS dark grey over anterior 2/3, yellowish posteriorly; urogomphi pale yellow; legs pale yellow.

Body. Measurements and ratios that characterize the body shape are shown in Table 3 .

Head. Head capsule ( Figs 43–44 ). Subovate, sides subparallel; frontoclypeus with 13–15 spatulate setae. Antenna ( Figs 45–46 ). A3’ finger-like.

Chaetotaxy. Seta FR3 subequal or longer than seta FR2; seta PA6 longer than seta PA7; seta PA13 longer than seta PA12; prementum with two additional setae on dorsal surface; setae TI2, TI3, TI6, TI7, TA6, and TA7 acute apically; seta AB2 shorter than seta AB9; seta AB15 subequal or shorter than seta AB11; setae UR2, UR3 and UR4 inserted contiguously; position and number of additional setae on legs are shown in Table 1 .

Instar II ( Fig. 78 ). As first-instar larva except as follows:

Color. Thoracic and abdominal segments dark brown with several yellowish maculae.

Body. Measurements and ratios that characterize the body shape are shown in Table 3 .

Head. Head capsule. Frontoclypeus with 28–31 spatulate setae. Antenna. A3’ bulge-like.

Chaetotaxy. Position and number of secondary setae on legs are shown in Table 2 ; parietale with 4–6 spine-like secondary setae along lateral margin; anterodorsal secondary setae on TI and TA acute apically.

Instar III ( Figs 60 , 67–68 , 72 , 81 ). As second-instar larva except as follows:

Body. Measurements and ratios that characterize the body shape are shown in Table 3 .

Head. Head capsule ( Fig. 60 ). Frontoclypeus with 40–51 spatulate setae.

Chaetotaxy. Position and number of secondary setae on legs are shown in Table 2 ; parietale with 4–6 spine-like secondary setae along lateral margin.

Ecology. Larvae were collected from eddies of clear mountain stream ( Fig. 87 ), particularly in road-side gutters with constantly flowing clear water ( Fig. 88 ). Larvae occur amongst fallen leaves deposited in the gutter.

Figures

FIGURES 43–44. Platambus sawadai (Kamiya, 1932), instar I, head capsule: (43) dorsal aspect (colour pattern not represented); (44) ventral aspect. EB, egg bursters; TP, tentorial pits. Numbers and lowercase letters refer to primary setae and pores, respectively. Scale bar = 0.10 mm.

FIGURES 45–51. Platambus sawadai (Kamiya, 1932), instar I, head appendages: (45–46) antenna, (45) dorsal aspect; (46) ventral aspect; (47–48) maxilla, (47) dorsal aspect; (48) ventral aspect; (49–50) labium; (49) dorsal aspect; (50) ventral aspect; (51) mandible, dorsal aspect. Numbers and lowercase letters refer to primary setae and pores, respectively; filled squares refer to additional setae. Scale bars = 0.10 mm.

FIGURES 57–60. Head capsule of selected species of Platambus Thomson, 1859, instar III, dorsal aspect: (57) P. pictipennis (Sharp, 1873); (58) P. convexus Okada, 2011; (59) P. fimbriatus (Sharp, 1884); (60) P. sawadai (Kamiya, 1932). Scale bar = 0.50 mm.

FIGURES 73–82. Dorsal habitus of selected species of Platambus Thomson, 1859: (73– 75) instar I; (76–78) instar II; (79-82) instar III; (73, 76, 79) P. pictipennis (Sharp, 1873); (74, 77, 80) P. fimbriatus (Sharp, 1884); (75, 78, 81) P. sawadai (Kamiya, 1932); (82) P. convexus Okada, 2011. Scale bar = 1.00 mm in (73–78), 2.00 mm in (79–82).

FIGURES 61–68. Prothoracic leg of selected species of Platambus Thomson, 1859, instar III: (61–62) P. pictipennis (Sharp, 1873), (61) anterior aspect; (62) posterior aspect; (63–64) P. convexus Okada, 2011, (63) anterior aspect; (64) posterior aspect; (65–66) P. fimbriatus (Sharp, 1884), (65) anterior aspect; (66) posterior aspect; (67–68) P. sawadai (Kamiya, 1932), (67) anterior aspect; (68) posterior aspect. Scale bar = 0.50 mm.

FIGURES 69–72. Last abdominal segment and urogomphi of selected species of Platambus Thomson, 1859, instar III, dorsal aspect: (69) P. pictipennis (Sharp, 1873); (70) P. convexus Okada, 2011; (71) P. fimbriatus (Sharp, 1884); (72) P. sawadai (Kamiya, 1932). Scale bar = 0.50 mm.

FIGURES 83–88. Collecting localities of the larvae of Platambus Thomson, 1859: (83–85) Echi river, Shiga Prefecture, Western Japan, (83) moderate sized river, with withered grass hanging; (84) river bank with gravel bed; (85) shallow area with dry grass deposited; (86) Nishinopporo-sawa river, Hokkaido Prefecture, Northern Japan, small stream flowing under broadleaved trees; (87–88) Happudani river, Shiga Prefecture, Western Japan, (87) mountain stream; (88) gutters with constantly flowing clear water.