Platambus convexus Okada, 2011

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 : 413-414

Description of the larvae of Platambus convexus Okada, 2011

Source of material. 4instar I,6instar III, Japan:Nishinopporo-sawa,Nopporo,Ebetsu-shi, Hokkaido Pref., 22.III.2014, 21.III.2015, R. Okada leg; 26.XII.2015, D. Sumikawa leg; Japan: Ishihoko riv., Hatori, Ten-ei-mura, Fukushima Pref., 26.X.2016, K. Hirasawa leg. First instar larvae were reared ex ovo from adults collected at that locality. The identification of instar III is firm as P. convexus is the only Platambus species found at those localities ( Okada 2011).

Diagnosis. First instar larva of P. convexus can be distinguished from the other species studied by the following combinations of features: frontoclypeus with more than 15 spatulate setae ( Fig. 15 ); seta FR3 shorter than seta FR2 ( Fig. 15 ); seta PA6 subequal in length to seta PA7 ( Fig. 15 ); primary seta LA10 inserted subapically ( Fig. 22 ); ratio L3/HW = 3.30–3.50. In addition to color patterns of head capsule ( Fig. 58 ), last abdominal segment, and urogomphi ( Figs 70 , 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 15–28 ). Color (alcohol preserved). Dorsal surface of head capsule predominantly creamy white; frontoclypeus creamy white apically, dark brown around each egg burster; parietale creamy white with a dark brown V-shaped macula across the ecdysial suture along with some pale brown maculae. Head appendages creamy white; thoracic and abdominal terga I to VII creamy white; LAS dark brown over anterior 1/2, paler posteriorly; urogomphi creamy white; legs creamy white.

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

Head. Head capsule ( Figs 15–16 ). Subovate, sides subparallel; frontoclypeus with 15–16 spatulate setae. Antenna ( Figs 17–18 ). A3’ protruding, finger-like.

Chaetotaxy. Seta FR3 shorter than seta FR2; seta PA6 shorter than seta PA7; seta PA13 subequal or longer than seta PA12; prementum with two additional setae on dorsal surface; setae TI2, TI3, TI6, TI7, TA6, and TA7 acute apically; seta AB2 subequal to seta AB9; seta AB15 longer 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. No specimen was available for study.

Instar III ( Figs 58 , 63–64 , 70 , 82 ). As first-instar larva except as follows:

Color. Dorsal surface of head capsule yellowish; parietale yellowish with W-shaped pale brown marking and pale spot maculae across distal margin of ecdysial suture; thoracic and abdominal segments pale brown with several pale yellowish maculae; LAS brown over anterior 1/2, yellowish posteriorly.

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

Head. Head capsule ( Fig. 58 ). Frontoclypeus with 42–45 spatulate setae. Antenna. A3’ bulge-like.

Chaetotaxy. Position and number of secondary setae on legs are shown in Table 2 ; parietale with 6–7 spine-like secondary setae along lateral margin.

Habitat. Larvae were collected along the quiet margin of a shallow creek flowing under broadleaved trees ( Fig. 86 ). Whereas frozen in winter, we were able to collect some larvae under ice.

Figures

FIGURES 15–16. Platambus convexus Okada, 2011, instar I, head capsule: (15) dorsal aspect (colour pattern not represented); (16) 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 17–23. Platambus convexus Okada, 2011, instar I, head appendages: (17–18) antenna, (17) dorsal aspect; (18) ventral aspect; (19–20) maxilla, (19) dorsal aspect; (20) ventral aspect; (21–22) labium; (21) dorsal aspect; (22) ventral aspect; (23) 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 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 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 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.