Rhantaticus congestus ( Klug, 1833 )

Alarie, Yves, Michat, Mariano C., Bergsten, Johannes & Hájek, Jiří, 2023, Morphology of the larvae of Rhantaticus congestus (Klug, 1833) and phylogenetic comparison with other known Aciliini (Coleoptera: Dytiscidae: Dytiscinae), Zootaxa 5380 (3), pp. 247-264 : 249-254

Description of the instar II and III larvae of Rhantaticus congestus ( Klug, 1833) ( Figs 1–23 )

Source of material. The larvae studied were associated with adults collected at the following localities: Madagascar: Toliara: RN10 15 km S. of junction RN7, Loc P44 , muddy zebu waterhole , 23.24257S 44.22927E, 17.v.2006, one instar III ( NHRS-JLKB 000076336), leg. J. Bergsten. Madagascar: Toliara: Menabe: Kirindy RS. 20.07476S 44.67075E, 49 m.a.o. 12.xii.2009, MAD09-45, one instar II ( NHRS-JLKB 000000097, DNA voucher), leg. J. Bergsten, N. Jönsson, T. Ranarilalatiana, J.H. Randriamihaja ; Madagascar: Toliara: Menabe: Kirindy RS. 20.07655S 44.67532E, 65 m.a.o. 12.xii.2009, MAD09-47, one instar III ( NHRS-JLKB 000000098), leg. J. Bergsten, N. Jönsson, T. Ranarilalatiana, J. H. Randriamihaja ; Madagascar: Mahanjaga: Melaky: btw Bekopaka –Antsalova . 18.91556S 44.55546E, 47 m.a.o. 16.xii.2009, MAD09-61, two instar II ( NHRS-JLKB 000075156), leg. J. Bergsten, N. Jönsson, T. Ranarilalatiana, J. H. Randriamihaja . Madagascar: Fianarantsoa: Plateau de l’Horombe , Nanarena vill. env; 22°30.1'S 45°45.6'E, 23.xi.2022, three instar II and nine instar III, leg. J. Hájek.

Description, instar II ( Figs 1–14 , 21–22 )

Color: Body predominantly creamy white to pale yellow; head capsule yellow, with a median piceous macula on frontoclypeus and parietal; head appendages creamy white to pale yellow; thoracic terga and legs pale yellow; abdominal terga yellow except abdominal tergum VIII black over posterior half; urogomphi black. It is worth noting, however, that two deviating larvae, both collected from a residual pool in a dried-out forest stream in a closed canopy deciduous forest, were darker in colouration. This could reflect that pigmentation is adaptable in R. congestus being darker in forest habitats and lighter in open landscape ones.

Body: Subcylindrical, bent at first abdominal segment, gibbous in lateral view. Measurements and ratios aimed to characterize the body shape as in Table 1 .

Head ( Figs 1–10 ): Head capsule ( Figs 1–2 ) flattened, subtriangular, longer than broad; maximum width at stemmata, not or slightly constricted at level of occipital region, HW/OCW = 2.29–2.39; occipital suture present, ecdysial line well marked; occipital foramen deeply emarginate both dorsally and ventrally; epicranial plates meeting ventrally, posterior tentorial pits visible ventrally on central region; surface smooth except for crescent-shaped microsculptures medially over occiput; frontoclypeus subtriangular, apical margin rounded medially; anterolateral lobes (= adnasalia) rounded, not projecting beyond nasale; six rounded dorsolateral stemmata at each side, stemmata protruding a short distance from head surface, two anterodorsal ones strongly developed. Antenna ( Figs 3–4 ) short, robust, four-segmented, half as long as HW; A1 and A3 subequal in length, longest; A3 with a strongly developed ventroapical spinula; A4 shortest, with spinula at mid-length, similar to that of A3; apical lateroventral process of A3 (A3’) not protruding; antennomeres not covered with short spine-like spinulae. Mandible ( Figs 5– 6 ) prominent, falciform, wide at base, sharp apically, with short-hair-like spinulae distally along inner margin; mandibular channel present, inner margin slightly toothed dorsally, more strongly ventrally. Maxilla ( Figs 7–8 ) with cardo well developed; stipes strongly developed, subtrapezoidal, antero-internal angle right-angled, not projecting inwards, internal margin with short spinulae; palpifer very short, broad, incompletely sclerotized; palpus short, robust, three-segmented, MP1 shortest, MP3 longest, MP1/MP2 = 0.69–0.74; MP3 with spinula similar to those of antenna; palpomeres smooth, not covered with scattered minute spinulae; galea well developed, spiniform, slightly curved inwards, surface covered with scattered minute spinulae, GA/MP1 = 2.90–3.19. Labium ( Figs 9–10 ) with prementum subtrapezoidal, somewhat pear-like, longer than broad, anterodorsal margin rounded, projecting forward into a unifid median process, not indented apically; dorsal surface of prementum densely covered with minute spine-like spinulae over apical and basal half; labial palpus short, robust, two-segmented, MP/LP = 0.66–0.69; palpomere 1 longest; palpomeres 1 and 2 with strong spine-like spinulae along external margin.

Thorax ( Figs 11–12 ): Terga convex, pronotum about as long as meso- and metanotum combined, meso- and metanotum subequal; protergite subrectangular, margins truncated, more developed than meso- and metatergite; meso- and metatergite transverse, with anterotransverse carina; sagittal line well marked; venter membranous; spiracles absent. Legs ( Figs 11–12 ): long, composed of six articles; L2 longest, slightly longer than subequal L1 and L3; CO robust, elongate, TR divided into two parts by an annulus, FE, TI and TA slender, subcylindrical, PT with two long, slender, almost straight claws, posterior claw shorter than anterior one; leg articles smooth, not covered with minute spine-like spinulae; ventral margin of protarsus with a row of well-developed spinulae along distal half; L3/HW = 2.89–3.05.

Abdomen ( Figs 13–14 ): Eight-segmented, segments I–VI sclerotized dorsally, membranous ventrally; segments III–V widest, remaining segments progressively narrowing to apex; tergites I–VII similar to each other, narrow, transverse, laterally rounded, with anterotransverse carina, sagittal line present on anterior third; segments VII–VIII completely sclerotized; spiracles absent on segments I–VII; segment VIII (= LAS) ( Fig. 13 ) longest, subtriangular, without anterotransverse carina, not covered with short spinulae; siphon reduced. Urogomphus ( Fig. 14 ) short, onesegmented, not covered with short spinulae; U/HW = 0.38–0.45.

Chaetotaxy ( Figs 1–14 ): Dorsal surface of head capsule with few short secondary setae ( Fig. 1 ); ventral surface of parietal with several spiniform setae ( Fig. 2 ); antennomere I with several secondary setae dorsally (as in Fig. 17 ); mandible with a row of elongate secondary hair-like setae along basoexternal margin ( Figs 5–6 ); dorsal surface of maxillary stipes with two rows of elongate spine-like setae, 20–21 along inner margin and 6–8 medially; numerous secondary hair-like setae present along the dorsoexternal margin of stipes ( Fig. 7 ); secondary leg setation detailed in Table 2 ; rows of secondary natatory setae present along posterodorsal margin and basal half of anteroventral margin of tarsi; posterior surface of femora and tibiae with linear row of minute secondary pores below the rows of natatory setae (not represented); abdominal segments VII–VIII with row of elongate natatory setae on lateral margin ( Fig. 13 ); LAS with secondary spine-like setae dorsally and ventrally ( Fig. 13 ).

Description, instar III ( Figs 15–20 , 23 )

As instar II except as follows:

Color: As in instar II ( Fig. 23 ).

Body: Measurements and ratios aimed to characterise the body shape as in Table 1 .

Head ( Figs 15–18 ): Head capsule not constricted at level of occipital suture, HW/OCW = 1.83–1.97. Antenna: A2 and A3 secondarily subdivided ( Fig.17 ). Maxilla: MP3 secondarily subdivided ( Fig. 18 ); MP1/MP2 = 0.90– 1.00; GA/MP1 = 2.36–2.54; MP/LP = 0.47–0.53.

Thorax ( Figs 19–20 ): Spiracles present on mesothorax. Legs ( Figs 19–20 ): L3/HW = 3.08–3.26.

Abdomen: Sagittal line and spiracles present on segments I–VII. Urogomphus: U/HW = 0.19–0.23.

Chaetotaxy ( Figs 15–20 ): Parietal with several ventral secondary spine-like setae ( Fig. 16 ); mandible with a larger number of minute secondary setae distally; dorsal surface of maxillary stipes 22–24 inner and 8–11 median spine-like setae ( Fig. 18 ); secondary leg setation detailed in Table 2 and Figs 19–20 .

Remarks: One instar II and two instar III larvae were CO1 sequenced along with two adults all collected in 2009. Latter two sequenced larvae were identical in 825bp of 3’ end of COI with each other and with one adult female whereas an adult male from MAD09-47 had 3 differences.

Habitat and collecting circumstances: Except for the two larvae from Kirindy RS collected from a residual pool in a dried-out forest stream in a closed canopy deciduous forest, all specimens studied were sampled in open landscape temporary pools and ponds such as the one represented in Fig. 24 (size ca. 1.5 x 1.0 m; maximal depth about 0.5 m; muddy bed, surrounded with short Cyperaceae plants).

Figures

FIGURE 24. Habitat of Rhantaticus congestus (Klug, 1833), temporary pool near Nanarena village, Plateau de l’Horombe.

FIGURES 1–10. Rhantaticus congestus (Klug, 1833), instar II: 1. head capsule, dorsal aspect; 2. head capsule, ventral aspect; 3. antenna, dorsal aspect; 4. antenna, ventral aspect; 5. mandible, dorsal aspect; 6. mandible, ventral aspect; 7. maxilla, dorsal aspect; 8. maxilla, ventral aspect; 9. labium, dorsal aspect; 10. Labium, ventral aspect. AN, antenna, FR, frontoclypeus; gAN, antennal group; gMX, maxillary group; LA, labium; LC, lamellae clypeales; MN, mandible; MX, maxilla; PA, parietal; TP, tentorial pits; sp, spinula. Numbers and lowercase letters refer to primary setae and pores, respectively. Scale bars = 0.5 mm (Figs 1–2); 0.1 mm (Figs 3–10).

FIGURES 11–14. Rhantaticus congestus (Klug, 1833), instar II: 11. mesothoracic leg, anterior surface; 12. mesothoracic leg, posterior surface. 13. abdominal segment VIII, dorsal aspect; 14 urogomphus, dorsal aspect. AB, abdominal segment VIII; CO, coxa; FE, femur; TA, tarsus; TI, tibia; TR, trochanter; UR, urogomphus. Numbers and lowercase letters refer to primary setae and pores, respectively. Scale bars = 0.2 mm (Figs 11–13); 0.1 mm (Fig. 14).

FIGURES 15-20. Rhantaticus congestus (Klug, 1833), instar III: 15. head, dorsal aspect; 16. head ventral aspect; 17. antenna, dorsal aspect; 18. maxilla, dorsal aspect; 19. mesocoxa and mesotrochanter, anterior surface; 20. mesocoxa and mesotrochanter, posterior surface. A, antennomere; MP, maxillary palpomere. Scale bars = 0.5 mm (Figs 15–16); 0.2 mm (Figs 17–20).

FIGURES 21-23. Rhantaticus congestus (Klug, 1833): 21. instar II, lateral aspect; 22. instar II, dorsal aspect; 23. instar III, lateral aspect. Scale bar = 5 mm.