Hydrophilidae, Latreille, 1802

Minoshima, Yûsuke & Hayashi, Masakazu, 2011, Larval morphology of the Japanese species of the tribes Acidocerini, Hydrobiusini and Hydrophilini (Coleoptera: Hydrophilidae), Acta Entomologica Musei Nationalis Pragae (suppl.) 51, pp. 1-118 : 108-110

4.4. Key to the known genera of the aquatic Hydrophilidae from Japan

Here we provide a preliminary generic key to all known larvae of the aquatic Japanese Hydrophilidae (i.e., representatives of the subfamily Hydrophilinae and the genus Coelostoma Brullé, 1835 of the subfamily Sphaeridiinae ). This key presumably works for all instars. The larvae of the genus Megagraphydrus Hansen, 1999 are unknown; larvae of the Japanese species of the tribe Anacaenini and of the genera Pelthydrus d’Orchymont, 1919 (Laccobiini) and Chasmogenus are also unknown. For Anacaena and Chasmogenus , we refer to previous studies ( RICHMOND 1920; WINTERBOURN 1973; ANDERSON 1976; ARCHANGELSKY 1997, 1999; ARCHANGELSKY & FIKÁČEK 2004). The knowledge on the larva of the genus Pelthydrus is based on the larva described by BERTRAND (1936) as Hydrophilidae genus 1 and only later assigned to Pelthydrus by BERTRAND (1974); moreover, as the larva does not fit other known Laccobiini larvae based on its morphology, its identification is doubtful and the genus Pelthydrus is therefore not included in the key.

1. Labium with well developed hypopharyngeal lobe; legs more or less reduced. Mostly terrestrial species. ...................................................... Subfamily Sphaeridiinae (part.)

– Labium without well developed hypopharyngeal lobe; legs sometimes short, but well developed. ..................................................................................................................... 2

2. Both mandibles similar in shape and with same number of inner teeth ( Figs. 33 C–D, 49B–C, 61B–C). .................................................................................................... 3

– Mandibles strongly asymmetrical, with different number of inner teeth on each mandible ( Figs. 11 B–C, 15D–E, 57B–C). .................................................................. 14

3. Median lobe of spiracular atrium deeply bifurcate ( HAYASHI 1986: Pl. 8I, HANSEN & RICHARDSON 1998: Fig. 12 ). Terrestrial species. ........ Subfamily Sphaeridiinae (part.)

– Median lobe of spiracular atrium simple, entire ( Fig. 5 ). ....................................... 4

4. Nasale with only one large tooth medially ( HAYASHI 2009a: Fig. 6A ). ...................... .......................................................................................... Coelostoma Brullé, 1835

– Shape of nasale variable (straight, weakly rounded, serrate, or with variable number of teeth; e.g., Figs. 13C , 29C , 46C , 55A , 56C ), never with a single median tooth. .... .............................................................................................................................. 5

5. Nasale with several distinct teeth ( Figs. 36C , 46C , 60C , 62B ). .................................... 6

– Nasale without distinct teeth, straight or slightly serrate ( Figs. 52C , 55A ). ......... 13

6. Ligula reduced, indistinct. .............................................. Amphiops Erichson, 1843

– Ligula well developed (e.g., Figs. 8F , 21F , 30F , 55H , 57F ). .................................. 7

7. Anterior corners of mentum strongly projecting anteriad ( Figs. 61F , 63G ); legs long, with fringes of long swimming hairs ( Fig. 64D ). ............ Sternolophus Solier, 1834

– Anterior corners of mentum not projecting anteriad ( Fig. 30F , 47B ); legs rather short to moderately long, without fringes of long swimming hairs ( Figs. 45 , 50C ). ....... 8

8. Proscutum with lateral lobes ( ARCHANGELSKY & FIKÁČEK 2004: Figs. 9 , 11 ); posterior margin of dorsal plate of abdominal segment 8 slightly to strongly trifid ( ARCHANGELSKY & FIKÁČEK 2004: Figs. 10 , 12 ). ..................................................................................... 9

– Proscutum without lateral lobes ( Figs. 3 , 6 ); posterior margin of dorsal plate of abdo- minal segment 8 straight to sinuate ( Figs. 32B , 41B , 48B ). ................................. 10

9. Inner edge of antennal socket with fringe-like seta ( ARCHANGELSKY & FIKÁČEK 2004: Fig. 3 ); proscutum with rounded lateral lobes ( ARCHANGELSKY & FIKÁČEK 2004: Fig. 9 ); abdominal segments without finger-like lateral projections ( ARCHANGELSKY & FIKÁČEK 2004: Fig. 1 ). .................................................... Anacaena Thomson, 1859

– Inner edge of antennal socket with trichoid seta; proscutum with flat lateral lobes ( ARCHANGELSKY & FIKÁČEK 2004: Fig. 11 ); abdominal segments with finger-like lateral projections ( ARCHANGELSKY 1997: Fig. 37A ). ............................. Crenitis Bedel, 1881

10. Frontal lines not converging towards base of head capsule (the lines widely separated at the base of head capsule) or widely U-shaped ( ARCHANGELSKY 1997: Fig. 34B; WIN- TERBOURN 1973: Fig. 4 ). ................................................ Paracymus Thomson, 1867

– Frontal lines converging towards base of head capsule, V-shaped or lyriform ( Figs. 29A , 35A , 48A ). .................................................................................................................. 11

11. Nasale strongly asymmetrical ( Figs. 38C , 42A ); mandibles with two inner teeth, distal one large, basal one smaller ( Figs. 42 C–D); head capsule with long scale-like setae ( Figs. 29 , 36 , 38 ). .......................................................... Helochares Mulsant, 1844

– Nasale slightly asymmetrical ( Fig. 46C ); mandibles with three inner teeth, distal two large, basal one smaller ( Figs. 49 B–C); head capsule without long scale-like setae ( Fig. 46 ). ............................................................................................................. 12

12. Dorsal and lateral surface of head capsule with densely arranged, strong tooth-like cuticular projections; abdominal segments with transverse rows of tubercles. ......... .................................................................................... Hydrocassis Fairmaire, 1878

– Dorsal and lateral surface of head capsule smooth, without densely arranged, strong tooth-like cuticular projections ( Fig. 48A ); abdominal segments without transverse rows of tubercles ( Figs. 1G , 6C ). ........................................ Hydrobius Leach, 1815

13. Abdominal segments with long lateral projections ( Fig. 51A ); spiracular atrium with long prostyli ( Fig. 54B ). .............................................. Hydrochara Berthold, 1827

– Thoracic and abdominal segments with several pairs of long setiferous projections ( HAYASHI 2009a: Figs. 10 A–B); spiracular atrium without distinct prostyli (e.g., Figs. 5 , 32B ). ......................................................................... Regimbartia Zaitzev, 1908

14. Abdominal segments with long lateral tracheal gills ( HAYASHI 2009a: Figs. 10 C–D); spiracular atrium reduced. ............................................................ Berosus Leach, 1817

– Abdominal segments without tracheal gills; spiracular atrium developed (e.g., Fig. 5 ). ............................................................................................................................. 15

15. Epistomal lobes strongly extended anteriorly; left lobe with dense series of stout setae on anterior margin, right lobe without setae ( ARCHANGELSKY 1997: Fig. 45A ). ......... ........................................................................................ Laccobius Erichson, 1837

– Epistomal lobe not or moderately extended anteriorly, setation of both lobes more or less the same ( Figs. 10C , 20C , 56C ). ................................................................... 16

16. Nasale almost straight, without distinct teeth or serrate margin ( Fig. 56C ); frontal lines U-shaped ( Fig. 58A ); anterior corners of mentum strongly projecting anteriad ( Fig. 57F ); abdominal segments without spinose prolegs. ........................................ .................................................................................... Hydrophilus Geoffroy, 1762

– Nasale not straight, with distinct teeth or serrate margin ( Figs. 10C , 15A ); frontal lines V-shaped to lyriform ( Figs. 9A , 25A ); anterior corners of mentum not projecting anteriad ( Fig. 26G ); abdominal segments with spinose prolegs ( Figs. 12 A–B, 28). ................ 17

17. Nasale serrate, with only one or two teeth ( Figs. 17A , 22C ). .......................................... ............................................................................................... Enochrus Thomson, 1859

– Nasale with several distinct teeth, without serrate margin ( Figs. 7C , 10C ). ............... 18

18. Nasale almost symmetrical ( ANDERSON 1976: Fig. 9 ). ........ Chasmogenus Sharp, 1882

– Nasale strongly asymmetrical ( Figs. 7C , 10C ). ............ Agraphydrus Régimbart, 1903

Figures

Fig. 33. Helochares (Helochares) pallens (MacLeay, 1825), third instar.A – clypeolabrum, dorsal view; B – antenna, dorsal view; C–D – mandibles, dorsal view; E – maxilla, dorsal view; F – maxilla, ventral view; G – labium, dorsal view; H – labium, ventral view.

Fig. 11. Head appendages of Agraphydrus narusei (Satô, 1960), third instar.A – antenna, dorsal view; B–C – mandibles, dorsal view; D – maxilla, dorsal view; E – maxilla, ventral view; F – labium, dorsal view; G – labium, ventral view.

Fig. 12. Agraphydrus narusei (Satô, 1960).A–B – prolegs, ventral view:A – first instar; B – third instar. C–D – shape of setae, dorsal view: C – median part of parietale, third instar, dorsal view; D – thoracic segments, first instar, dorsal view. Seta on PA8 and PA13 missing. Photographs were taken with compound light microscope.

Fig. 5. Spiracular atrium of Enochrus japonicus (Sharp, 1873). A – dorsolateral view; B – lateral view.

Fig. 6. Habitus of third instar larvae of the Acidocerini and Hydrobiusini, dorsal view.A – Enochrus umbratus Sharp, 1884; B – Helochares nipponicus Hebauer, 1995; C – Hydrobius pauper Sharp, 1884.

Fig. 13. Head capsule of Enochrus (Holcophilydrus) simulans (Sharp, 1873), first instar.A – dorsal view; B – ventral view; C – detail of anterior margin of head capsule, dorsal view.

Fig. 29. Head capsule of Helochares (Helochares) pallens (MacLeay, 1825), first instar.A – dorsal view; B – ventral view; C – detail of anterior margin of head capsule, dorsal view.

Fig. 46. Head capsule of Hydrobius pauper Sharp, 1884, second instar.A – dorsal view; B – ventral view; C – detail of anterior margin of head capsule, dorsal view.

Fig. 55. Hydrochara affinis (Sharp, 1873), third instar. A – clypeolabrum, dorsal view; B – antenna, dorsal view; C – antenna, detail of outer membranous area on pedicel; D–E – mandibles, dorsal view; F – maxilla, dorsal view; G – maxilla, ventral view; H – labium, dorsal view; I – labium, ventral view.

Fig. 56. Head capsule of Hydrophilus acuminatus Motschulsky, 1854, first instar.A – dorsal view; B – ventral view; C – detail of anterior margin of head capsule, dorsal view.

Fig. 36. Head capsule of Helochares (Hydrobaticus) anchoralis Sharp, 1890, first instar.A – dorsal view; B – ventral view; C – detail of anterior margin of head capsule, dorsal view.

Fig. 60. Head capsule of Sternolophus (Sternolophus) rufipes (Fabricius, 1792), first instar. A – dorsal view; B – ventral view; C – detail of anterior margin of head capsule, dorsal view.

Fig. 62. Sternolophus (Sternolophus) rufipes (Fabricius, 1792), third instar, dorsal view. A – head; B – detail of anterior margin of head capsule; C – spiracular atrium.

Fig. 52. Head capsule of Hydrochara affinis (Sharp, 1873), first instar.A – dorsal view; B – ventral view; C – detail of anterior margin of head capsule, dorsal view.

Fig. 8. Head appendages of Agraphydrus narusei (Satô, 1960), first instar. A – antenna, dorsal view; B–C – mandibles, dorsal view; D – maxilla, dorsal view; E – maxilla, ventral view; F – labium, dorsal view; G – labium, ventral view.

Fig. 21. Enochrus (Holcophilydrus) umbratus Sharp, 1884, third instar.A – antenna, dorsal view; B–C – mandibles, dorsal view; D – maxilla, dorsal view; E – maxilla, ventral view; F – labium, dorsal view; G – labium, ventral view.

Fig. 30. Head appendages of Helochares (Helochares) pallens (MacLeay, 1825), first instar. A – antenna, dorsal view; B–C – mandibles, dorsal view; D – maxilla, dorsal view; E – maxilla, ventral view; F – labium, dorsal view; G – labium, ventral view.

Fig. 57. Head appendages of Hydrophilus acuminatus Motschulsky, 1854, first instar. A – antenna, dorsal view; B–C – mandibles, dorsal view; D – maxilla, dorsal view; E – maxilla, ventral view; F – labium, dorsal view; G – labium, ventral view.

Fig. 61. Head appendages of Sternolophus (Sternolophus) rufipes (Fabricius, 1792), first instar. A – antenna, dorsal view; B–C – mandibles, dorsal view; D – maxilla, dorsal view; E – maxilla, ventral view; F – labium, dorsal view; G – labium, ventral view.

Fig. 63. Head appendages of Sternolophus (Sternolophus) rufipes (Fabricius, 1792), third instar. A – antenna, dorsal view; B – detail of outer surface of pedicel, lateral view; C–D – mandibles, dorsal view; E – maxilla, dorsal view; F – maxilla, ventral view; G – labium, dorsal view; H – labium, ventral view.

Fig. 64. Prosternum and mesothoracic legs of Hydrophilini species.A – prosternum of Hydrochara affinis (Sharp, 1873), third instar, ventral view. B–D – mesothoracic legs, first instar, anterior view: B – Hydrochara affinis (Sharp, 1873); C – Hydrophilus acuminatus Motschulsky, 1854; D – Sternolophus rufipes (Fabricius, 1792).

Fig. 47. Head appendages of Hydrobius pauper Sharp, 1884, second instar. A – antenna, dorsal view; B – labium, dorsal view; C – labium, ventral view.

Fig. 45. Mesothoracic legs of Acidocerini species, third instar, anterior view.A – Agraphydrus narusei (Satô, 1960); B – Enochrus umbratus Sharp, 1884; C – Enochrus japonicus (Sharp, 1873); D – Helochares nipponicus Hebauer, 1995.

Fig. 50.Thoracic structures of Hydrobius pauper Sharp, 1884, third instar.A – surface of proscutum; B – prosternum, ventral view; C – mesothoracic leg, anterior view.

Fig. 9. Agraphydrus narusei (Satô, 1960), third instar.A – head, dorsal view; B – spiracular atrium, dorsal view.

Fig. 10. Head capsule of Agraphydrus narusei (Satô, 1960), third instar.A – dorsal view; B – ventral view; C – detail of anterior margin of head capsule, dorsal view.

Fig. 3. Larva of Enochrus japonicus (Sharp, 1873) with basic morphological terms. A – dorsal view; B – lateral view; C – ventral view.

Fig. 32. Helochares (Helochares) pallens (MacLeay, 1825), third instar. A – head, dorsal view; B – spiracular atrium, dorsal view.

Fig. 41. Helochares (Hydrobaticus) nipponicus Hebauer, 1995, third instar. A – head, dorsal view; B – spiracular atrium, dorsal view.

Fig. 48. Hydrobius pauper Sharp, 1884, third instar. A – head, dorsal view; B – spiracular atrium, dorsal view; C – detail of anterior margin of head capsule, dorsal view.

Fig. 1. Habitus of the third instar larvae of Acidocerini and Hydrobiusini. A – Agraphydrus narusei (Satô, 1960), dorsal and lateral view; B – Enochrus (Holcophilydrus) simulans (Sharp, 1873), dorsal view; C – E. (H.) umbratus Sharp, 1884, dorsal view; D – E. (Methydrus) japonicus (Sharp, 1873), dorsal view; E – Helochares (Helochares) pallens (MacLeay, 1825), dorsal view; F – H.(Hydrobaticus) nipponicus Hebauer, 1995, dorsal view; G – Hydrobius pauper Sharp, 1884, dorsal and ventral view.

Fig. 37. Head appendages of Helochares (Hydrobaticus) anchoralis Sharp, 1890, first instar. A – antenna, dorsal view; B–C – mandibles, dorsal view; D – maxilla, dorsal view; E – maxilla, ventral view; F – labium, dorsal view; G – labium, ventral view.

Fig. 34. Helochares (Helochares) pallens (MacLeay, 1825), chaetotaxy of head capsule, dorsal view. A – median part of head capsule, second instar. B–D – third instar larva: B – median part of head capsule; C – intraspecific variation of secondary sensilla between PA6 and PA7; D – intraspecific variation of secondary sensilla on outer part of antennal socket. Secondary sensilla are marked by a black rhombus.

Fig.4.General morphology of the head and mouthparts of theAcidocerini,Hydrobiusini and Hydrophilini.A–C – head and anterior part of thorax, schematic:A – dorsal view; B – ventral view; C – lateral view. D–G – head appendages, dorsal view: D – antenna; E – mandible; F – maxilla; G – labium (submentum omitted).

Fig. 35. Helochares (Hydrobaticus) anchoralis Sharp, 1890, first instar.A – head, dorsal view; B – spiracular atrium, dorsal view.

Fig. 38. Head capsule of Helochares (Hydrobaticus) nipponicus Hebauer, 1995, first instar. A – dorsal view; B – ventral view; C – detail of anterior margin of head capsule, dorsal view.

Fig. 42. Helochares (Hydrobaticus) nipponicus Hebauer, 1995, third instar.A – clypeolabrum, dorsal view; B – antenna, dorsal view; C–D – mandibles, dorsal view; E – maxilla, dorsal view; F – maxilla, ventral view; G – labium, dorsal view; H – labium, ventral view.

Fig. 49.Head appendages of Hydrobius pauper Sharp, 1884, third instar.A – antenna, dorsal view; B–C – mandibles, dorsal view; D – maxilla, dorsal view; E – maxilla, ventral view; F – labium, dorsal view.

Fig. 51. Habitus of Hydrophilini species, third instar, dorsal view. A – Hydrochara affinis (Sharp, 1873); B – Sternolophus rufipes (Fabricius, 1792).

Fig. 54. Hydrochara affinis (Sharp, 1873), third instar. A – head, dorsal view; B – spiracular atrium, dorsal view.

Fig. 20. Head capsule of Enochrus (Holcophilydrus) umbratus Sharp, 1884, third instar.A – dorsal view; B – ventral view; C – detail of anterior margin of head capsule, dorsal view.

Fig. 58. Hydrophilus acuminatus Motschulsky, 1854, third instar. A – head, dorsal view; B – spiracular atrium, dorsal view.

Fig.15. Enochrus (Holcophilydrus) simulans (Sharp, 1873), second instar.A – clypeolabrum,dorsal view; B – antenna, dorsal view; C – antenna, detail of outer membranous area on pedicel, ventral view; D–E – mandibles, dorsal view; F – maxilla, dorsal view; G – maxilla, ventral view; H – labium, dorsal view; I – labium, ventral view.

Fig. 25. Enochrus (Methydrus) japonicus (Sharp, 1873), third instar. A – head, dorsal view; B – spiracular atrium, dorsal view.

Fig. 26. Enochrus (Methydrus) japonicus (Sharp, 1873), third instar. A – clypeolabrum, dorsal view; B – antenna, dorsal view; C–D – mandibles, dorsal view; E – maxilla, dorsal view; F – maxilla, ventral view; G – labium, dorsal view; H – labium, ventral view.

Fig. 17. Enochrus (Holcophilydrus) simulans (Sharp, 1873), third instar.A – clypeolabrum, dorsal view; B – antenna, dorsal view; C–D – mandibles, dorsal view; E – maxilla, dorsal view; F – maxilla, ventral view; G – labium, dorsal view; H – labium, ventral view.

Fig. 22. Head capsule of Enochrus (Methydrus) japonicus (Sharp, 1873), first instar. A – dorsal view; B – ventral view; C – detail of anterior margin of head capsule, dorsal view.

Fig. 7. Head capsule of Agraphydrus narusei (Satô, 1960), first instar. A – dorsal view; B – ventral view; C – detail of anterior margin of head capsule, dorsal view.