Platambus fimbriatus ( Sharp, 1884 )

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 : 414-418

Description of the larvae of Platambus fimbriatus ( Sharp, 1884)

Source of material. 1 instar I, 1 instar II, 10 instar III, Japan: Echi riv., Tanesato, Notogawa-cho, Shiga Pref., 22.II.2015; 20.XII.2015; 10.I.2016; R. Okada leg; 5 instar I, 1 instar II, Japan: Abukuma riv., Tsuruo, Saigo-mura , Fukushima Pref., 8.I.2017 R. Okada leg. Larvae were identified ex societate imaginis. Both Platambus fimbriatus and P. pictipennis occur at these two localities. Larvae of P. fimbriatus , however, could readily be recognized using features listed below.

Diagnosis. First instar larva of P. fimbriatus can be distinguished from the other species studied by the following combinations of features: frontoclypeus with less than 10 spatulate setae ( Fig. 29 ); seta FR3 shorter than seta FR2 ( Fig. 29 ); seta PA6 subequal in length to seta PA7 ( Fig. 29 ); primary seta LA10 inserted subapically ( Fig. 36 ); setae TI2, TI3, TI6, TI7, TA6, and TA7 bluntly pointed apically; seta UR4 not inserted contiguously to setae UR2 and UR3; ratio L3/HW <2.90. In addition to color patterns of head capsule ( Fig. 59 ), last abdominal segment, and urogomphi ( Figs 71 , 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 29–42 , 74 ). Color. Dorsal surface of head capsule predominantly dark brown; frontoclypeus yellowish anteriorly, dark brown around each egg burster; parietale dark brown, pal- er over occipital region; head appendages pale yellow, A3, A4, MP3, MP2, MP3 and LP2 infuscate apically; thoracic and abdominal terga I to VII pale brown; LAS predominantly dark brown; urogomphi pale yellow basally, dark brown over distal half; legs predominantly pale yellow, dark brown apically.

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

Head. Head capsule ( Figs 29–30 ). Rounded, sides slightly diverging posteriorly; frontoclypeus with 10 spatulate setae. Antenna ( Figs 31–32 ). A3’ finger-like.

Chaetotaxy. Seta FR3 shorter than seta FR2; seta PA6 subequal or longer than seta PA7; seta PA13 shorter than PA12; prementum with one additional seta on dorsal surface; setae TI2, TI3, TI6, TI7, TA6, and TA7 bluntly pointed apically; seta AB2 shorter than seta AB9; seta AB15 longer than seta AB11; seta UR4 not inserted contiguously to setae UR2 and UR3; position and number of additional setae on legs are shown in Table 1 .

Instar II ( Fig. 77 ). As first-instar larva except as follows:

Color. Dorsal surface of LAS yellowish anteriorly, dark brown over posterior half.

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

Head. Head capsule. Frontoclypeus with 20–21 spatulate setae. Antenna. A3’ bulge-like.

Chaetotaxy. Position and number of secondary setae on legs are shown in Table 1 ; parietale with 4 spine-like secondary setae on lateral margin of each side; anterodorsal secondary setae on TI and TA bluntly pointed apically.

Instar III ( Figs 59 , 65–66 , 71 , 80 ). As second-instar larva except as follows:

Color. Dorsal surface of head capsule yellowish; parietale yellowish with a narrow V-shaped dark brown marking across capsule at about mid-length and some brown maculae posteriorly; pro- and mesotergum and abdominal segments yellowish with several brown maculae, metanotum predominantly dark brown; LAS yellowish anteriorly, dark brown over distal 1/3 to 1/2; urogomphi predominantly yellow.

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

Head. Head capsule ( Fig. 59 ). Frontoclypeus with 26–31 spatulate setae.

Chaetotaxy. Position and number of secondary setae on legs are shown in Table 1 ; parietale with 6–8 spine-like secondary setae along lateral margin.

Habitat. Larvae occur along quiet margins of moderate sized rivers flowing on sandy bottom. First-instar larvae are mainly collected along the banks under stones in shallow water. Whereas also collected in shallow parts, both second- and third- instar larvae appear to be more abundant in dry grass deposits ( Fig. 85 ).

Figures

FIGURES 29–30. Platambus fimbriatus (Sharp, 1884), instar I, head capsule: (29) dorsal aspect (colour pattern not represented); (30) 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 31–37. Platambus fimbriatus (Sharp, 1884), instar I, head appendages: (31–32) antenna, (31) dorsal aspect; (32) ventral aspect; (33–34) maxilla, (33) dorsal aspect; (34) ventral aspect; (35–36) labium; (35) dorsal aspect; (36) ventral aspect; (37) 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.