Platambus Thomson, 1859

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 : 403-406

Description of the larvae of Platambus Thomson, 1859

Diagnosis. Larvae of Platambus are characterized by the following combination of characters: cephalic capsule with neck constriction ( Figs 1, 2 , 15, 16 , 29, 30 , 43, 44 , 57–60 ); occipital suture absent; pore FRe absent ( Figs 1 , 15 , 29 , 43 ); A3 lacking a ventroapical spinula, A3’ protruding, bulge-like to finger-like ( Figs 4 , 18 , 32 , 46 ); galea present, stipes with additional setae present or absent ( Figs 5–6 , 19–20 , 33–34 , 47–48 ); prementum broader than long ( Figs 7–8 , 21–22 , 35 –36,49–50); legs lacking natatory setae ( Figs 61–68 ); femur with several additional setae ( Figs 10–11 , 24–25 , 38–39 , 52–53 ); setae FE5, TI6 and TI7 short, spine-like ( Figs 11 , 25 , 39 , 53 ); LAS subquadrate, siphon lacking ( Figs 12–13 , 26–27 , 40–41 , 54–55 , 69–72 ); urogomphi composed of one urogomphomere, lacking secondary setae, with primary seta UR5 much shorter than seta UR 7 in instar I larva ( Figs 14 , 28 , 42 , 56 ).

Instar I( Figs 1–56 , 73–75 ). Body. Subcylindrical, narrowing towards abdominal apex. Measurements and ratios that characterize the body shape are shown in Table 3 .

Head. Head capsule ( Figs 1–2 , 15–16 , 29–30 , 43–44 ). HL = 0.64–0.92 mm; HW = 0.59–0.75 mm; FRL = 0.22–0.41 mm. Flattened, rounded or subovate, about as broad as long (HL/HW = 1.04–1.27), maximum width at level of stemmata, sides subparallel or slightly diverging posteriorly; neck constriction present; occipital suture absent; ecdysial line well marked, coronal line long, 0.45–0.65 times HL; occipital foramen broadly emarginate ventrally, HW/OCW = 1.74–2.47; frontoclypeus subtriangular, rounded mesally, extending medially beyond level of anterolateral lobes of frontoclypeus [= adnasalia of Beutel (1994)]; dorsal surface with two spine-like egg bursters [= ruptor ovi of Bertrand (1972)] posteriorly, less than half as broad basally than maximum width of antennomere 1; anterior margin with 10–16 spatulate setae [= lamellae clypeales of Bertrand (1972)] variable in size; gular suture not visible; ocularium present, with six stemmata, four visible dorsally and two ventrally, arranged into two curved vertical rows; tentorial pits visible ventrally on each side at about mid-length. Antenna ( Figs 3–4 , 17–18 , 31–32 , 45–46 ). Slender, shorter than HW (A/HW = 0.60–0.83), composed of four antennomeres; A1 and A4 the shortest (A4/A1 = 0.83–1.37); A3 the longest (A4/A3 = 0.58–0.94); A3’ protruding, bulge- or finger-like. Mandible ( Figs 9 , 23 , 37 , 51 ). Prominent, broad basally, distal half projected inwards, sharp apically, 0.44–0.53 times as long as HL; mandibular channel present. Maxilla ( Figs 5–6 , 19–20 , 33–34 , 47–48 ). Cardo small, subovate; stipes short, broad, with minute spinulae proximad to galea; galea well developed, subconical, lacinia absent; palpifer short, palpomere-like, with dorsodistal spinulae; palpus 3-segmented, shorter than antenna (A/MP = 1.13–1.37), MP1 and MP2 the shortest, subequal, MP3 the longest (MP3/MP2 = 1.51–2.06). Labium ( Figs 7–8 , 21–22 , 35–36 , 49–50 ). Prementum subrectangular, broader than long, with minute spinulae on dorsal and ventral surfaces; palpus elongate, 2-segmented, subequal to shorter than maxillary palpus (MP/LP = 1.08–1.47); LP2 longer than LP1 (LP2/LP1 = 1.17–2.00).

Thorax. Terga convex, pronotum slightly shorter than meso- and metanotum combined, meso- and metanotum subequal, wider than pronotum; protergite subrectangular, margins rounded, more developed than meso- and metatergites; meso- and metatergites transverse, with anterotransverse carina; sagittal line visible on the three tergites; thoracic sterna membranous, spiracles absent. Legs ( Figs 10–11 , 24–25 , 38–39 , 52–53 ). Long, well developed, composed of six segments (including pretarsus), L1 the shortest, L3 the longest; L3 = 1.61–2.37 mm, L3/HW = 2.66–3.48; CO robust, elongate, TR divided into two parts, FE, TI and TA slender, subcylindrical; pretarsus with two long, slender, slightly curved claws, posterior claw shorter than anterior one on L1 and L2, claws subequal in length on L3; claws lacking basoventral spinulae; TI and TA with marginal spinulae variably developed.

Abdomen. 8-segmented; segments I–VII sclerotized dorsally, membranous ventrally; tergites I–VII narrow, transverse, rounded laterally, with sagittal line, with anterotransverse carina, covered with minute spinulae in transverse rows; spiracles absent on segments I–VII; LAS ( Figs 12–13 , 26–27 , 40–41 , 54–55 ). Short, subquadrate, completely sclerotized, ring-like, with anterotransverse carina dorsally and laterally (LAS = 0.16–0.27 mm, LAS/HW = 0.25–0.37), covered with minute spinulae in transverse rows; siphon reduced to almost lacking. Urogomphi. ( Figs 14 , 28 , 42 , 56 ). U = 0.70–1.17 mm, U/HW = 1.18–1.68, one-segmented, longer than LAS (U/LAS = 4.11–6.00), without or with microspinulae.

Chaetotaxy ( Figs 1–56 ). Similar to that of generalized Agabinae larva ( Alarie 1995, 1998; Alarie & Larson 1998; Alarie et al. 1998, 2019; Michat & Archangelsky 2009) except for the following characteristics: seta FR5 close to pore FRd; pore ANi located more distally; A3 with one minute structure (possibly a spinula) posterior to seta AN2; a minute structure (possibly a pore) present on dorsal surface of A4; prementum with one or two additional setae on dorsal surface; seta FE1 inserted sub-medially; seta FE6 hair-like; femora with a variable number of additional setae ( Table 1 ); despite thorough effort setae AB7 and AB14 could not be found, so they were coded as absent but with some hesitation; setae UR2 and UR3 contiguously inserted; seta UR4 either contiguously inserted to setae UR2 and UR3 or more distant; pore URc and one additional minute seta located near the articulation of setae UR5–UR8; setae UR5 and UR6 shorter than setae UR7 and UR8.

Instar II ( Figs 76–78 ). As first-instar larva except as follows:

Head. HL = 0.95–1.35 mm; HW = 0.85–1.14 mm; FRL = 0.40–0.56 mm. Head capsule. Subovate to subtrapezoidal (HL/HW = 1.11–1.24, HW/OCW = 1.88–2.30); frontoclypeus with 20–31 spatulate setae; egg bursters lacking. Antenna. A/HW = 0.60–0.72; A4 the shortest, A3 the longest (A4/A3 = 0.44–0.66). Maxilla. MP3 the longest (MP3/MP2 = 1.17–1.54); Labium. MP/LP = 1.10–1.29; LP2 subequal or longer than LP1 (LP2/LP1 = 1.00–1.47).

Thorax. Legs. L3 = 2.56–3.64 mm, L3/HW = 2.89–3.43.

Abdomen. Segment VII completely sclerotized, ring-like; LAS = 0.34–0.57 mm, LAS/HW = 0.38–0.52. Urogomphi. U = 1.29–1.69 mm, U/HW = 1.27–1.62, longer than LAS (U/LAS = 2.56–4.12); U5, U6, U7 and U8 subequal or U8 slightly shorter than the others.

Chaetotaxy. Cephalic capsule with several minute secondary setae; parietale with 4–8 spine-like secondary setae on the lateral margin and several spine-like setae on ventral surface; mandible with one hair-like secondary seta along external margin, proximal to pore MNa, and some minute secondary setae along external margin; stipes with one minute secondary seta on ventral surface, near setae MX 2 and MX 3; prementum with one secondary pore on ventral surface, near seta LA1; CO with one secondary pore on posterior surface; LAS with numerous secondary setae on dorsal and lateral surfaces; secondary leg setation represented in Table 2 .

Instar III ( Figs 57–72 , 79–82 ). As second-instar larva except as follows:

Head ( Figs 57–60 ). HL = 1.40–1.99 mm; HW = 1.21–1.64 mm; FRL = 0.61–0.77 mm. Frontoclypeus with 26–51 spatulate setae in a double low along anterior margin. Antenna, A1, A2 and A3 the longest, subequal (A4/A3 = 0.29–0.53); A3’ bulge-like. Maxilla. MP1, MP2 and MP3 subequal in length; Labium. LP2 shorter to longer than LP1 (LP2/LP1 = 0.73–1.20).

Thorax. Spiracular openings present on mesothorax. Legs ( Figs 61–68 ). L3 = 3.87–5.51 mm, L3/HW = 3.03– 3.81.

Numbers between slash marks refer to pro-, meso- and metathoracic leg, respectively.

Abdomen. Spiracular openings present on segments I–VII; LAS = 0.73–1.12 mm, LAS/HW = 0.55–0.77. Urogomphi ( Figs 69–72 ). U = 1.88–2.78 mm, U/HW = 1.24–1.84; U/LAS = 1.88–2.86.

Chaetotaxy ( Figs 57–72 ). Stipes with 1–2 minutes secondary setae; prementum with two secondary pores; CO with two secondary pores; Secondary leg setation represented in Table 1 and Figures 61–68 .

Figures

FIGURES 1–2. Platambus pictipennis (Sharp, 1873), instar I, head capsule: (1) dorsal aspect (colour pattern not represented); (2) 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 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 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 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 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 3–9. Platambus pictipennis (Sharp, 1873), instar I, head appendages: (3–4) antenna, (3) dorsal aspect; (4) ventral aspect; (5–6) maxilla, (5) dorsal aspect; (6) ventral aspect; (7–8) labium; (7) dorsal aspect; (8) ventral aspect; (9) 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 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 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 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 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 10–14. Platambus pictipennis (Sharp, 1873), instar I: (10–11) metathoracic leg; (10) anterior aspect; (11) posterior aspect; (12–13) last abdominal segment; (12) dorsal aspect; (13) ventral aspect; (14) urogomphi, dorsal aspect. Numbers and lowercase letters refer to primary setae and pores, respectively; filled squares refer to additional setae. Scale bars = 0.20 mm in (10–11), 0.10 mm in (12–14).

FIGURES 24–28. Platambus convexus Okada, 2011, instar I: (24–25) metathoracic leg; (24) anterior aspect; (25) posterior aspect; (26–27) last abdominal segment; (26) dorsal aspect; (27) ventral aspect; (28) urogomphi, dorsal aspect. Numbers and lowercase letters refer to primary setae and pores, respectively; filled squares refer to additional setae. Scale bars = 0.20 mm in (24–25), 0.10 mm in (26–28).

FIGURES 38–42. Platambus fimbriatus (Sharp, 1884), instar I: (38–39) metathoracic leg; (38) anterior aspect; (39) posterior aspect; (40–41) last abdominal segment; (40) dorsal aspect; (41) ventral aspect; (42) urogomphi, dorsal aspect. Numbers and lowercase letters refer to primary setae and pores, respectively; filled squares refer to additional setae. Scale bars = 0.20 mm in (38–39), 0.10 mm in (40–42).

FIGURES 52–56. Platambus sawadai (Kamiya, 1932), instar I: (52–53) metathoracic leg; (52) anterior aspect; (53) posterior aspect; (54–55) last abdominal segment; (54) dorsal aspect; (55) ventral aspect; (56) urogomphi, dorsal aspect. Numbers and lowercase letters refer to primary setae and pores, respectively; filled squares refer to additional setae. Scale bars = 0.20 mm in (52–53), 0.10 mm in (54–56).

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).

Tables

TABLE 3. Number and position of additional setae of selected species of Platambus Thomson, 1859: PIC = P. pictipennis (Sharp, 1873); CON = P. convexus Okada, 2011; FIM = P. fimbriatus (Sharp, 1884); SAW = P. sawadai (Kamiya, 1932); AV = anteroventral, PV = posteroventral, Total = total number of additional and secondary setae on segment; n = number of specimens examined.

Measure						Instar	I								Instar II										Instar III
	PIC			CON			FIM		SAW			PIC			FIM		SAW			PIC			CON			FIM			SAW
	(n = 14)			(n = 4)			(n = 6)		(n = 7)			(n = 10)			(n = 2)		(n = 10)			(n = 10)			(n = 6)			(n = 10)			(n = 11)
HL (mm)	0.70	-	0.78	0.84	-	0.86	0.64	- 0.71	0.86	-	0.92	1.04	-	1.19	0.95	- 1.00	1.23	-	1.35	1.56	-	1.80	1.86	-	1.92	1.40	-	1.52	1.79	-	1.99
HW (mm)	0.62	-	0.71	0.67	-	0.71	0.59	- 0.64	0.70	-	0.75	0.90	-	1.01	0.85	- 0.89	1.02	-	1.14	1.33	-	1.47	1.38	-	1.51	1.21	-	1.33	1.50	-	1.64
FRL (mm)	0.31	-	0.37	0.29	-	0.40	0.22	- 0.37	0.31	-	0.41	0.41	-	0.56	0.40	- 0.51	0.45	-	0.55	0.67	-	0.77	0.64	-	0.76	0.61	-	0.75	0.67	-	0.74
OCW (mm)	0.31	-	0.38	0.29	-	0.38	0.32	- 0.36	0.31	-	0.40	0.45	-	0.51	0.41	- 0.43	0.44	-	0.55	0.59	-	0.73	0.69	-	0.74	0.58	-	0.71	0.65	-	0.73
HL/HW	1.09	-	1.18	1.21	-	1.27	1.04	- 1.10	1.16	-	1.27	1.14	-	1.20	1.11	- 1.11	1.17	-	1.24	1.18	-	1.29	1.27	-	1.35	1.10	-	1.23	1.18	-	1.27
HW/OCW	1.78	-	2.09	1.74	-	2.47	1.76	- 1.97	1.80	-	2.38	1.93	-	2.14	2.00	- 2.16	1.88	-	2.30	2.02	-	2.33	2.01	-	2.07	1.89	-	2.26	2.11	-	2.35
A/HW	0.70	-	0.83	0.77	-	0.83	0.60	- 0.69	0.68	-	0.73	0.64	-	0.72	0.60	- 0.63	0.61	-	0.72	0.55	-	0.65	0.64	-	0.71	0.50	-	0.58	0.57	-	0.63
A4/A1	0.96	-	1.26	0.88	-	1.00	1.09	- 1.37	0.83	-	1.25	0.67	-	0.84	0.73	- 0.90	0.51	-	0.65	0.41	-	0.50	0.30	-	0.39	0.42	-	0.56	0.33	-	0.40
A4/A3	0.70	-	0.83	0.64	-	0.69	0.78	- 0.94	0.58	-	0.76	0.51	-	0.59	0.64	- 0.66	0.44	-	0.54	0.37	-	0.45	0.29	-	0.34	0.43	-	0.53	0.32	-	0.39
A/MP	1.22	-	1.37	1.15	-	1.19	1.13	- 1.27	1.13	-	1.20	1.25	-	1.39	1.27	- 1.30	1.17	-	1.28	1.32	-	1.39	1.23	-	1.36	1.26	-	1.41	1.24	-	1.35
MP3/MP2	1.51	-	1.78	1.52	-	1.75	1.70	- 2.06	1.66	-	1.94	1.17	-	1.46	1.43	- 1.54	1.33	-	1.54	0.96	-	1.10	1.08	-	1.29	1.04	-	1.18	1.04	-	1.22
MP3/MP1	1.70	-	2.14	1.87	-	2.13	1.77	- 2.13	1.90	-	2.43	1.35	-	1.76	1.52	- 1.90	1.51	-	1.84	1.05	-	1.26	1.17	-	1.28	1.07	-	1.22	1.20	-	1.32
MP/LP	1.12	-	1.37	1.31	-	1.47	1.08	- 1.25	1.20	-	1.39	1.13	-	1.26	1.10	- 1.16	1.15	-	1.29	1.10	-	1.25	1.25	-	1.38	1.04	-	1.24	1.12	-	1.23
LP2/LP1	1.17	-	1.57	1.75	-	2.00	1.26	- 1.44	1.33	-	1.63	1.01	-	1.20	1.04	- 1.14	1.00	-	1.47	0.84	-	0.95	0.94	-	1.20	0.73	-	1.02	0.83	-	1.05
L3 (mm)	1.88	-	2.19	2.31	-	2.37	1.61	- 1.81	2.21	-	2.36	2.84	-	3.19	2.56	- 2.72	3.23	-	3.64	4.24	-	4.77	5.15	-	5.51	3.87	-	4.11	4.85	-	5.26
L3/HW	2.90	-	3.21	3.33	-	3.48	2.66	- 2.87	3.07	-	3.33	2.89	-	3.22	3.00	- 3.04	3.05	-	3.43	3.13	-	3.29	3.60	-	3.81	3.03	-	3.28	3.09	-	3.40
L3/L1	1.24	-	1.30	1.29	-	1.32	1.22	- 1.29	1.25	-	1.36	1.28	-	1.38	1.30	- 1.35	1.28	-	1.42	1.34	-	1.42	1.42	-	1.46	1.30	-	1.36	1.36	-	1.41
L3 (CO/FE)	0.92	-	1.02	0.91	-	0.96	0.90	- 0.96	0.88	-	1.02	0.92	-	1.02	0.87	- 0.89	0.91	-	0.95	0.92	-	0.99	0.85	-	0.92	0.89	-	0.98	0.87	-	0.99
L3 (TI/FE)	0.64	-	0.74	0.68	-	0.72	0.59	- 0.65	0.69	-	0.77	0.66	-	0.73	0.59	- 0.62	0.67	-	0.76	0.66	-	0.71	0.66	-	0.70	0.55	-	0.63	0.67	-	0.76
L3 (TA/FE)	0.81	-	0.90	0.84	-	0.87	0.66	- 0.79	0.87	-	0.93	0.72	-	0.81	0.68	- 0.71	0.76	-	0.85	0.67	-	0.75	0.68	-	0.71	0.59	-	0.66	0.77	-	0.82
L3 (CL/TA)	0.58	-	0.70	0.45	-	0.49	0.66	- 0.81	0.39	-	0.48	0.45	-	0.65	0.72	- 0.79	0.41	-	0.46	0.40	-	0.50	0.40	-	0.51	0.63	-	0.74	0.34	-	0.41
LAS (mm)	0.16	-	0.21	0.20	-	0.23	0.16	- 0.19	0.22	-	0.27	0.34	-	0.46	0.37	- 0.41	0.47	-	0.57	0.73	-	0.91	1.00	-	1.12	0.77	-	0.90	0.93	-	1.06
LAS/HW	0.25	-	0.31	0.29	-	0.33	0.25	- 0.31	0.30	-	0.37	0.38	-	0.47	0.43	- 0.45	0.45	-	0.52	0.55	-	0.62	0.70	-	0.77	0.62	-	0.70	0.60	-	0.67
U (mm)	0.88	-	1.08	0.99	-	1.08	0.70	- 1.00	1.04	-	1.17	1.29	-	1.51	1.33	- 1.38	1.43	-	1.69	1.92	-	2.24	2.40	-	2.78	1.88	-	2.28	1.92	-	2.40
U/HW	1.33	-	1.68	1.39	-	1.61	1.18	- 1.60	1.47	-	1.58	1.27	-	1.55	1.49	- 1.62	1.33	-	1.55	1.38	-	1.58	1.68	-	1.84	1.50	-	1.81	1.24	-	1.53
U/LAS	4.86	-	6.00	4.45	-	5.28	4.19	- 5.44	4.11	-	5.09	2.84	-	4.12	3.29	- 3.75	2.56	-	3.28	2.26	-	2.86	2.25	-	2.62	2.24	-	2.71	1.88	-	2.47