Hydrophiloidea, Latreille, 1802

Minoshima, Yûsuke N. & Watanabe, Reiya, 2020, Morphology of immature stages of Helophorus (Gephelophorus) auriculatus (Coleoptera, Helophoridae), Acta Entomologica Musei Nationalis Pragae 60 (1), pp. 319-332 : 331

of Japanese Hydrophiloidea

All families of Hydrophiloidea except Epimetopidae are recorded from Japan (HANඌൾN 1999, KıŦANƟ et al. 2019). Although the larvae of Japanese species of Georissidae , Hydrochidae and Spercheidae are not described, larvae of the Japanese hydrophiloid families may be identified using the following key (adapted from RıർIJMƟNĐ 1920, BøඏıNǤ & HൾNRıĸඌൾN 1938, ARർIJANǤൾĿඌĸY 1997):

1. Abdominal segment 9 complete ( Fig. 5E ; see also fig. 6A, C in Archangelsky 1997 for Georissidae , which has slightly reduced segment 9), thus segments 8 to 10 not forming spiracular atrium; antenna with two sensoria (SE1 and SE2) on outer face of the intersegmental membrane between antennomeres 2 and 3 ( Figs 4A , 7A ). ................................................. 2

– Abdominal segment 9 modified as part of the spiracular atrium, not or only partly visible from dorsal view, thus segments 8 to 10 forming spiracular atrium (spiracular atrium highly reduced in hydrophilid genus Berosus Leach, 1817 , e.g., fig. 5D in Minoshima & Hayashi 2015); antenna with one sensorium (SE1) on outer face of the intersegmental membrane between antennomeres 2 and 3 (often SE1 is reduced in size and very small; e.g., fig. 53A in Minoshima & Hayashi 2011). .......... 3

2. Legs well developed, five-segmented ( Figs 5C, D ); urogomphi well developed, long, three-segmented ( Fig. 5E ). ............................................. Helophoridae

– Legs reduced, minute, three-segmented (fig. 8A in Archangelsky 1997); urogomphi reduced. .................. ................................................................. Georissidae

3. Inner tooth of mandible situated close to mandibular apex, thus mandibular apex looks bifid; inner face of stipes strongly extending anteromesally, forming well developed, large inner lobe (lacinia); labium developed; mentum fused with prementum, forming plate-like structure ( Archangelsky 1997, 2001; Fikáček 2019a); legs five-segmented, very long. ........ ................................................................ Spercheidae

– Inner tooth of mandible situated on median part, thus mandibular apex simple; inner face of stipes not extending anteromesally or weakly extending anteromesally, forming small inner lobe (lacinia) (see Archangelsky 1997); labium well developed or reduced; if labium well developed, mentum not fused with prementum (rarely fused but not in Japanese species); legs variable, minute to long. .................... 4

4. Submentum fused with head capsule (Figs 2B, 6B); antennomere 1 variable in length but never very long and stout ( Archangelsky 1997, Minoshima & Hayashi 2011); second segment of the labial palpus without a large sensorium; legs usually well developed in aquatic species, moderately to highly reduced in some terrestrial groups ( Arriaga-Varela et al. 2017, Archangelsky 2018, Minoshima 2019) ....................... ............................................................. Hydrophilidae

– Submentum not fused with head capsule; antennomere 1 very long and stout; second segment of labial palpus with two large sensoria of almost same size as the second palpomere; legs well developed, fivesegmented ( Richmond 1920, Archangelsky 1997, Fikáček 2019b). .................................... Hydrochidae

Figures

Fig. 5. Larvae of Helophorus auriculatus Sharp, 1884. A – head, second instar larva, dorsal (left) and ventral (right) view; B – head, third instar larva, dorsal (left) and ventral (right) view; C – posterior leg, first instar, anterior view; D – posterior leg, third instar, anterior view; E – abdominal apex, third instar, dorsal view.

Fig. 4. First instar larva of Helophorus auriculatus Sharp, 1884. Head appendages. A, B – antenna, dorsal (A) and ventral (B) view; C–E – mandibles (C – right mandible, dorsal view, D – right mandible, ventral surface (drawn from dorsal), E – left mandible, dorsal view); F–H – maxilla (F – ventral view, gMX omitted; G, H – maxilla, slightly modified by pressure of cover glass for examination, dorsal (G) and ventral (H) face, both drawn from dorsal view). I–K – labium, dorsal (I), dorsolateral (J), ventral (K) view.

Fig. 7. Third instar larva of Helophorus auriculatus Sharp, 1884.A – antenna, dorsal (left) and ventral (right) surface, both drawn from dorsal view, gAN omitted; B – mandible, dorsal view; C – ventral surface of basal part of mandible; D – maxilla, dorsal (left) and ventral (right) surface, both drawn from dorsal view; E – labium, dorsal view (left) and labium and its adjacent structure, ventral view (right), gAN omitted.