Agraphydrus narusei ( Satô, 1960 )

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 : 17-26

Agraphydrus narusei ( Satô, 1960)

( Figs. 1A , 7–12 , 44A , 45A )

Material examined. JAPAN: HONSHÛ: Shimane-ken : 14 L1, Inome , Inome-chô, Izumo-shi, 7.vi.2008 (egg cases collected in the field), 9.vi.2008 (date of fixation), MH ; 2 L1, same locality, 22.vii.2008, MH ; 2 L3, same locality, 29.vii.2008, MH ; 1 L1, downstream of Inome-gawa river , Inome-chô, Izumo-shi, 7.vi.2008, MH .

General morphology. Third instar. Body slender, almost parallel-sided ( Fig. 1A ). Colour. Head and sclerotised parts light yellowish brown; membranous parts milky white ( Fig. 1A ).

Head ( Fig. 9A ). Head capsule subquadrate. Frontal lines V-shaped, fused at base of head capsule, coronal line short. Surface of head capsule smooth. Six stemmata closely aggregated on each anterolateral portion of head capsule. Clypeolabrum asymmetrical. Nasale with six teeth, three on right side more closely aggregated and projecting further than three on left. Epistomal lobes asymmetrical, not projecting further than nasale; each epistomal lobe emarginate medially, right lobe projecting further than left lobe.

Antenna ( Fig. 11A ) 3-segmented, slender. Scape slightly longer than pedicel. Flagellum the shortest, small.

Mandibles ( Figs. 11 B–C) asymmetrical; right mandible with two inner teeth, distal one large, slightly bifurcated at apex, weakly serrate on margins, basal one small; inner face of right mandibular apex weakly serrate. Left mandible with one large inner tooth, slightly bifurcated at apex, weakly serrate around margin; inner face of left mandibular apex serrate.

Maxilla ( Figs. 11 D–E) 6-segmented (including cardo), distinctly longer than antenna. Cardo small, irregularly shaped. Stipes the longest, longer than palpomeres 1–4 combined; a small spine-like cuticular projection on apical part of inner face of stipes. Maxillary palpus 4-segmented; palpomere 1 the widest, incompletely sclerotised on dorsal surface; palpomere 2 the shortest, slightly shorter than palpomere 4, wider than palpomeres 3 and 4; palpomere 3 longer and wider than palpomere 4, narrower than palpomere 2; inner process largely sclerotised.

Labium ( Figs. 10B , 11 F–G) well developed. Submentum ( Fig. 10B ) fused to head capsule, large, subpentagonal, wider than mentum. Mentum subquadrate, longer and wider than prementum, with dense and rather short cuticular spines on dorsal surface. Prementum subtrapezoidal. Ligula shorter than labial palpi, largely sclerotised. Labial palpi about as long as prementum.

Thorax. Prothorax wider than head capsule ( Fig. 1A ). Proscutum formed by a large plate subdivided by fine sagittal line, with scale-like setae, anterior and posterior margins weakly sclerotised. Prosternum subpentagonal, with incomplete, short, fine sagittal line in basal half ( Fig. 44A ). Mesonotum with incomplete sagittal line, with two dorsal sclerites on each side; anterior sclerite small, narrow, posterior sclerite large, each sclerite with long to short setae, some of setae scale-like (e.g., Fig. 12D ). Metanotum with one large dorsal sclerite on each side, with very to moderately long setae, some of them scale-like in shape. Legs rather short, visible in dorsal view, 5-segmented, bearing short as well as moderately long setae, lacking swimming hairs ( Fig. 45A ); all three pairs similar in shape.

Abdomen. Abdomen 10-segmented, almost parallel-sided, covered with fine pubescence on membranous parts; segments 1 to 7 similar in shape and size ( Fig. 1A ). Abdomen mostly membranous, dorsal and lateral sclerites undetectable, dorsal sclerites slightly visible on first segment only; abdominal segments 1 to 7 with scale-like setae on each side, four very long setae situated on posterior half; segments 3 to 7 with spinose prolegs, spines of prolegs stout and curved ( Fig. 12B ).

Spiracular atrium ( Fig. 9B ): Segment 8 with oval dorsal plate bearing three setae on each side: two very long on lateral margin, one rather short on median part; one very long seta on each side of segment 8. Posterior edge of dorsal plate almost rounded, median part with two small projections bearing two short setae; procercus incompletely sclerotised, bearing two rather short setae and one long seta. Segment 9 trilobed, partially sclerotised; each lateral lobe with rather short, membranous acrocercus bearing one long seta apically; urogomphi short, one segmented, with one very long seta on apical membranous area; prostyli reduced.

First instar. Similar to third instar larva, more weakly sclerotised than in third instar.

Head ( Fig. 7 ). Right epistomal lobe weakly emarginate medially; left epistomal lobe strongly projecting and sharply pointed apically.

Antenna short, stout ( Fig. 8A ); stouter than in third instar. Scape about as long as pedicel.

Mandibles ( Figs. 8 B–C): Distal inner tooth of right mandible serrate on margin; inner face of right mandibular apex serrate; inner tooth of left mandible serrate on margins.

Maxilla ( Figs. 8 D–E): Maxillary palpomere 2 the shortest, palpomere 3 as long as palpomere 4, palpomere 4 longer than palpomeres 1 and 2.

Labium ( Figs. 8 F–G): Prementum about as long as mentum.

Thorax. Mesonotal plate with one long, scale-like seta, and four very long and two moderately long trichoid setae on each sclerite; metanotal plate with one long, scale-like seta, and three very long and one or two long trichoid setae on each sclerite.

Primary chaetotaxy of head. Frontale altogether with 41 sensilla ( Figs. 7A, C ). Central part with three pairs of sensilla divergent posteriad; FR 1 rather short seta close to frontal line; FR 2 pore-like, situated anteromesally to FR 1 at midlength between FR 1 and FR 3; FR 3 short seta, situated even more anteriorly and slightly more mesally than FR 2. Moderately long setae ( FR 5–6) and pore-like sensillum FR 4 situated slightly posteromesally to antennal socket; FR 6 longer than FR 5. Seta FR 7 moderately long, close to inner margin of antennal socket; FR 4, FR 6 and FR 7 forming a triangular group. Nasale with a group of six stout, short setae (gFR1), lateral-most seta on each side placed in grooves between nasale and epistomal lobes. Epistomal lobes altogether with five setae (gFR2); right lobe with two short setae; left lobe with three short setae, inner one slightly shorter than remaining ones. FR 15 pore-like, situated posteriorly to median setae of nasale; seta FR 8 long, situated posteriorly to FR 15. Two setae ( FR 9 and FR 12) and one pore-like sensillum ( FR 14) forming a triangular group situated medioanteriorly to antennal socket; FR 9 long, scale-like; FR 12 short, stout. Seta FR 10 rather long, placed slightly anteriorly to FR 4; FR 12 at midlength between FR 9 and FR 13. Inner part of epistomal lobes with two pore-like sensilla ( FR 11 and FR 13); FR 11 situated anteriorly to FR 13.

Parietale with 30 sensilla each ( Figs. 7 A–B). Posterior portion of dorsal surface with a group of four sensilla ( PA 1–4) in longitudinal row at midwidth; PA 3 pore-like, between short setae PA 2 and PA 4; seta PA 1 short, situated posteriorly to PA 2–4. Seta PA 5 short, situated anterolaterally to PA 1–4. PA 6 pore-like, located posteromesally, more distant from posterior margin of head than PA 1. PA 7, PA 12 and PA 13 forming a closely aggregated triangular group located at midlength between antennal socket and posterior margin of head. Seta PA 7 very long, scale-like (e.g., Fig. 12C ); seta PA 12 rather long; seta PA 13 very long. PA 8 and PA 10 situated posteriorly to antennal socket; PA 8 more closely to frontal line than PA 10; seta PA 8 very long, scale-like; sensillum PA 10 pore-like, situated close to PA 8. Seta PA 9 long, scale-like, situated close to outer margin of antennal socket. Two pore-like sensilla ( PA 15 and PA 17) and three setae ( PA 11, PA 14, and PA 16) situated laterally in anterior third of parietale; PA 11 short, PA 14 and PA 16 very long, scale-like; PA 16 longer than PA 14; PA 11, PA 14, and PA 15 situated more dorsally than PA 16 and PA 17. Anterior corner of head capsule with four pore-like sensilla ( PA 19 and PA 23–25) and three long to very long setae ( PA 20–22); PA 19–21 dorsolateral, PA 22–25 ventrolateral; PA 19 situated anteromesally to PA 21, PA 20 very long, trichoid, between PA 19 and PA 21, PA 21 very long, scale-like; PA 22 long, trichoid, PA 25 situated anteromesally to PA 22–24, close to ventral mandibular acetabulum; PA 24 at midlength between PA 25 and PA 23; PA 23 at midlength between PA 22. Seta PA 18 very long, located laterally on posterior third of parietale. Two setae ( PA 26 and PA 28) and pore-like sensillum PA 27 situated at midlength of parietale on ventral surface; PA 26 very long, trichoid; PA 28 very long, scale-like; PA 27 at midlength between PA 26 and PA 28. Pore-like sensilla PA 29 located ventrally on posterior fourth of parietale, behind PA 28; pore-like sensilla PA 30 located laterally on posterior third of parietale, behind PA 18.

Antenna ( Fig. 8A ): Antennomere 1 with five pore-like sensilla ( AN 1–5); AN 1 situated on basal 0.36 of dorsolateral face, AN 2 on distal third of dorsal surface; AN 3–5 on distal margin, AN 3 lateral, AN 4 on inner face, AN 5 ventral. Antennomere 2 with one pore-like sensillum ( AN 6) situated dorsally close to distal margin of sclerite and five setae ( AN 7–11) on intersegmentary membrane between antennomeres 2 and 3; AN 7 short, rounded apically, AN 8 short, rather stout, AN 9 minute; AN 7–9 on outer face of antenna next to sensorium ( SE 1); setae AN 10–11 on inner face of antenna; AN 10 long, scale-like, AN 11 short, stout, both setae close to each other. SE 1 rather large, slightly shorter than antennomere 3. Antennomere 3 with five setae (gAN) on apical membranous area: two long and three short setae.

Mandible ( Figs. 8 B–C) with two setae ( MN 1 and MN 5) and four pore-like sensilla ( MN 2–4 and MN 6). MN 1 long, on outer face of mandible. Sensilla MN 2–4 pore-like, forming a triangular group at midlength of dorsal surface; MN 2 at midlength between MN 1 and MN 3; MN 4 on lateral face. Seta MN 5 minute, situated at midlength of outer mandibular face between MN 4 and MN 6. MN 6 situated subapically on inner face of mandible.

Maxilla ( Figs. 8 D–E): Cardo with one long ventral seta ( MX 1). Stipes with a row of five rather short, stout setae ( MX 7–11) situated dorsally along inner face; MX 7–11 equidistant, MX 11 more distant than MX 7–11 from each other; MX 8–11 with small subapical tooth. Stipes with two pore-like sensilla ( MX 2 and MX 3) situated ventrally on about basal fourth; three sensilla ( MX 4–6) situated subapically on outer face; MX 4 pore-like sensillum, MX 5 long, scale-like seta, MX 6 long, trichoid seta. Palpomere 1 with one moderately short spiniform seta ( MX 16) situated basally on dorsal inner face, and with pore-like sensillum ( MX 12) and two long setae ( MX 13–14) on ventral surface; MX 13 on outer face of anterior corner; MX 14 between MX 13 and MX 15. Two pore-like sensilla ( MX 15 and MX 17) on membrane behind inner appendage; MX 17 dorsal, MX 15 ventral. Inner appendage with one long, scale-like seta and two trichoid setae (gAPP). Palpomere 2 with two pore-like sensilla ( MX 18–19) and a minute seta ( MX 27); MX 18 ventral, MX 19 dorsal; MX 27 on outer face of posterolateral corner. Palpomere 3 with one very long seta at midlength of dorsal surface, and with two pore-like sensilla ( MX 20 and MX 22) and one long, trichoid seta ( MX 21) on ventral surface; MX 22 at midlength of ventral surface, MX 20 and MX 21 close to distal margin of sclerite. Palpomere 4 with one long seta ( MX 24) on inner face of basal part, and with a digitiform sensillum ( MX 25) and a pore-like sensillum ( MX 26) situated subapically on outer face of sclerite; MX 25 dorsal, MX 26 ventral. Apical membranous area of palpomere 4 with several minute setae (gMX).

Labium ( Figs. 7B , 8 F–G): Submentum ( Fig. 7B ) with two pairs of setae ( LA 1–2); LA 1 very long in lateral corners, LA 2 short on anterior lobes ( Fig. 7B ). Ventral surface of mentum with two pairs of sensilla ( LA 3 and LA 4) on lateral part; LA 3 rather long seta in posterior two-fifths; LA 4 pore-like sensilla in anterior third. Dorsal surface of prementum with one pair of pore-like sensilla ( LA 8) at midwidth in posterior two-fifths of sclerite. Ventral surface of prementum with three pairs of sensilla close to lateral face; seta LA 5 short, on posterolateral corner; LA 6 long, situated anteriorly to LA 5; LA 7 pore-like, close to distal margin of sclerite. Membrane between prementum and palpi with one pair of long setae ( LA 10) on base of ligula, and one pair of minute setae ( LA 9) close to distal margin of sclerotised part of prementum. Ligula with one pair of small seta-like sensilla ( LA 12) on apical part, and with one pair of pore-like sensilla ( LA 11) in basal part of ventral surface. Palpomere 1 with one minute seta ( LA 13) in basal part of outer face; LA 14 situated dorsally on intersegmentary membrane between palpomeres 1 and 2. Palpomere 2 with one pore-like sensillum ( PA 15) situated subapically on outer face. Apical membranous area of palpomere 2 with one long seta and five moderately long setae (gLA).

Secondary chaetotaxy of head. Third instar. Parietale ( Figs. 10 A–B): One rather short secondary seta close to frontal line, at midlength between PA 6 and PA 8 but mesally of line connecting PA 6 and PA 8. One rather long secondary seta situated close to PA 8, anteriorly to line connecting PA 8 and PA 10. One rather long secondary seta and one pore-like secondary sensillum close to outer margin of antennal socket, seta close to PA 9, pore-like sensillum close to PA 19. One rather short secondary seta situated posteriorly to PA 21; one rather long secondary seta situated at midlength between PA 14 and PA 15, but posteriorly to line connecting PA 14 and PA 15. One pore-like secondary sensillum close to PA 16; one rather long secondary seta between PA 16 and PA 18, close to PA 18.

Mandible ( Figs. 11 B–C): Outer face of mandible with two short secondary setae, one close to MN 1, one posterior to MN 1; basal part of mandible with four rather short secondary setae on outer part.

Maxilla ( Figs. 11 D–E): Outer face of stipes with three trichoid secondary setae, one very long on distal part, one rather long in basal two-thirds. One rather short secondary seta on inner part of ventral surface, in distal fourth.

Labium: Dorsal surface of mentum ( Fig. 11F ) with four rather short, stout secondary setae on lateral portion, one on distal margin, three on median part; one pair of rather short secondary setae situated medially on distal margin of dorsal surface of mentum; one short secondary seta situated ventrally in anterior corner of ventral surface of mentum ( Fig. 11G ).

Habitat. Running water. Egg cases were found on the undersides of rocks. Larvae were found under rocks on the wet ground next to streams. It is possible that they live above the water level ( HAYASHI 2009a).

Identification. Three species of Agraphydrus are known from Japan, one in the Ryûkyû Islands ( SW Japan), two in Honshû, Shikoku and Kyûshû. Only one species of Agraphydrus , A. narusei was collected from the collecting sites together with the larvae used for the above description. This species usually co-occurs with representatives of the genera: Hydrocassis Fairmaire, 1878 (tribe Sperchopsini ), Crenitis Bedel, 1881 (tribe Anacaenini ) and Laccobius Erichson, 1837 (tribe Laccobiini ) whose larvae are easily distinguishable from the Agraphydrus larvae ( BØVING & HENRIKSEN 1938; MORIOKA 1955; BERTRAND 1972, 1977; ARCHANGELSKY 1997; ARCHANGELSKY & FIKÁČEK 2004).

Figures

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. 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.

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. 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. 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. 44. Prosterna of Acidocerini species, third instar, ventral view. A – Agraphydrus narusei (Satô, 1960); B – Enochrus umbratus Sharp, 1884; C – Helochares nipponicus Hebauer, 1995.

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.