Hydrocassis lacustris (Sharp, 1884)

Minoshima, Yûsuke & Hayashi, Masakazu, 2011, Larval morphology of the genus Hydrocassis Fairmaire (Coleoptera: Hydrophilidae), Journal of Natural History 45 (45 - 46), pp. 2757-2784 : 2776-2779

Hydrocassis lacustris (Sharp, 1884)

Figures 1A , 2 , 3 , 6–9 , 12C,D , 13A,C

Material examined

Japan: 1 L? ( SEHU), Yunosato, Shiriuchi-chô , Hokkaidô, 19 June 2008 H. Yoshitomi leg ; 1 L1, 2 L3 ( EUMJ, SEHU), Yazawa-sawa, Kuroiso , Tochigi pref., 25 July 1994, M. Satô leg. ; 1 L1 ( EUMJ), Shiga-kôgen, Yamanouchi-machi , Nagano pref., 4–5 August 1978, no collector data ; 12 L1, 4 L2 (reared from egg case) ( SEHU), small stream near Abe-tôge, Umegashima, Aoi-ku , Shizuoka-shi , Shizuoka prefecture, altitude 1380 m, 35 ◦ 18.81 ′ N, 138 ◦ 20.96 ′ E, 22 June 2008 (egg case collected), Y. Minoshima leg. ; 1 L3 ( EUMJ), Dando-uradani , 15 July 1998, no collector data ; 1 L3 ( EUMJ), Serŷo-toge , Kyôto, 6 August 1980, no collector data ; 1 L1, 1 L2, 3 L3 ( HGFC, SEHU), Shinji-gawa R., Matsue-shi , Shimane pref., 5 May 2007, M. Hayashi leg. ; 1 L3 ( SEHU), Mount Ôyorogi-san, Kadosaka, Iinan-chô , Shimane pref., 31 July 2007, M. Hayashi leg.

Description of general morphology – third instar

Slide preparations of three specimens were examined.

Colour ( Figure 1A ). Dorsal surface of head light brown, lighter in median and anterior parts of frontale and around stemmata, with two pairs of dark brown spots on medioposterior portion; light brown on ventral surface. Pronotum light brown, median portion darkened, the size of dark portion variable, sometimes resembles H. jengi ( Figure 1B ); mesothoracic and metathoracic terga and abdominal segments dark brown, darker than head, slightly lighter medially and laterally, looking like two dark longitudinal lines along the body; dorsal sclerite and tubercles of abdominal segments darker than those on other abdominal portions; dorsal sclerite of abdominal segment 8 dark brown in median portion. Ventral surface of thorax and abdomen light brown, proscutum and legs darkened.

Head. Posterior 0.5 to 0.6 of head capsule bearing dense, small but strong tooth-like cuticular projections on dorsal and lateral surfaces behind stemmata ( Figure 9B ). Nasale usually with five teeth, median tooth very small, sometimes absent, then nasale with four teeth. Epistomal lobes projecting about as far as nasale, right lobe with dense rather long spine-like cuticular projections on inner margin; left lobe with dense, short spine-like cuticular projections on inner margin.

Antenna. Antennomeres 1 and 2 covered with fine hair-like cuticular projections ( Figures 7A , 9C ). Antennomere 1 the longest, longer than antennomeres 2 and 3 combined. Antennomere 2 about half as long as antennomere 1.

Maxilla ( Figure 7D, E ). Dorsal surface of maxillary palpomeres 1–3 bearing sparse to rather dense fine hair-like cuticular projections.

Labium ( Figure 7F, G ). Ligula slightly shorter than palpi.

Abdomen. Segment 1 with three transverse rows of tubercles behind the sclerites ( Figure 6E ); the first row with five tubercles on each side, size of the tubercles from median to lateral one: large (L), small (S), rather L, S, L; second row with four tubercles on each side, inner three more closely situated than outer one: rather L, L, rather L, L; third row with three large tubercles on each side, outer one projecting laterally. Arrangement of tubercles on segments 2 to 5 similar to that on segment 1 but the tubercles of first and second transverse rows somewhat larger than those on segment 1: rather L, rather S, rather L, rather L, L in first row; rather L, L, L, L in second row. Segment 6 similar to segments 1 to 5 but first row composed of four rather large tubercles. Segment 7 with three transverse rows of tubercles, first row with four tubercles on each side, outer two closely situated: rather L, rather L, rather L, L; second row with four tubercles, inner three closely located: S, L, S, L; third row with two tubercles on each side, outer one projecting laterally.

Description of general morphology – second instar

Slide preparations of two specimens were examined. Similar to third instar, more weakly sclerotized than in third instar.

Head. Antenna moderately long, rather slender. Antennomere 2 about 0.5 to 0.6 times as long as antennomere 1.

Maxilla. Dorsal surface of maxillary palpomeres 1 and 2 sparsely covered with fine hair-like cuticular projections.

Abdomen. Abdominal transverse rows of tubercles smaller than in third instar. Description of general morphology – first instar

Slide preparations of eight specimens were examined. Similar to third instar, more weakly sclerotized than in second instar.

Head ( Figure 2 ). Frontal lines almost reaching to antennal socket.

Antenna ( Figure 3A ). Rather short and stout, bearing fine hair-like cuticular projections on ventral surface of antennomere 2. Antennomere 1 wider than antennomere 2, as long as antennomere 2.

Abdomen. Abdominal transverse rows of tubercles smaller than in second instar; inner two pairs of tubercles of the second row on segments 1 to 5 reduced, hardly recognizable.

Description of chaetotaxy of head – second instar

Frontale. Central part bearing numerous, rather short secondary setae (e.g. Figure 9B ). Each epistomal lobe with a group of seven to eight moderately long, stout setae (gFR2), inner two slightly shorter than outer ones.

Parietale. Bearing many secondary sensilla, on dorsal and lateral parts (e.g. Figure 9A, B ).

Mandible. With several small secondary setae on lateral part; basal part of mandible with four to five short secondary setae (e.g. Figure 7B, C ).

Maxilla. Stipes with 10–12 long secondary setae on outer face; one of them very long, close to MX 4–6 (e.g. Figure 7D, E ).

Labium. Mentum with 9–12 stout secondary setae each anterolateral corner; a trichoid secondary seta on ventral close to and outside of LA4 (e.g. Figure 7F, G ).

Description of chaetotaxy of head – third instar

Frontale. Central part bearing many, rather short and stout secondary setae ( Figure 9B ). Each epistomal lobe with a group of seven to eight moderately long, stout setae (gFR2), inner two slightly shorter than outer ones.

Parietale. Bearing numerous, rather short and stout secondary sensilla each, on dorsal and lateral parts ( Figure 9A, B ).

Mandible ( Figure 7B, C ). With rather sparse, small secondary setae on lateral part; basal part of mandible with five short secondary setae, three on dorsal and lateral, two on ventral.

Maxilla ( Figure 7D, E ). Stipes with 13–15 long secondary setae on outer margin. Labium ( Figure 7F, G ). Mentum with 8–12 stout secondary setae on each anterolateral corner.

Habitat

Running water ( Figure 13A ). Egg cases were found on the underside of rocks or leaves on the margins of a stream ( Figure 13C ); larvae usually hide behind rocks or leaves.

Identification

Hydrocassis lacustris is the only species of the genus distributed from Hokkaidô to Kyûshû Islands. Therefore, we identified the larvae collected from Honshû as H. lacustris . Instars of the larvae collected in the field were identified by sorting the specimens according the size of their head capsule and by comparison with the larvae of the known instar reared from egg cases collected in the field.

Remarks

Morioka (1955) published a description of the larva of “ Hydrocyclus sp. ” based on the specimens collected in Shiga and Tochigi Prefectures, Honshû. This larva corresponds in all characters with our material of H. lacustris . Later, Yoshimura (1959) described the larva collected in Nara Prefecture, Honshû as “ Hydrocyclus sp. B ”. Based on his description, his material differs substantially from Hydrocassis and belongs most probably to the genus Sternolophus Solier, 1834 .

Figures

Figure 1. Habitus of Hydrocassis larvae, dorsal and ventral views. (A) Hydrocassis lacustris Sharp, third instar; (B) Hydrocassis jengi Satô, second instar; (C) Hydrocassis uncinata Ji et Schödl, third instar.

Figure 2. Primary chaetotaxy of head capsule of Hydrocassis lacustris Sharp, first instar. (A) Dorsal view; (B) ventral view; (C) detail of anterior margin of head capsule, dorsal view.

Figure 3. Primary chaetotaxy of head appendages of Hydrocassis lacustris Sharp, first instar. (A) Right antenna, dorsal view; (B) left mandible, dorsal view; (C) left maxilla, dorsal view; (D) left maxilla, ventral view; (E) labium, dorsal view; (F) labium, ventral view. Black square indicates additional sensilla.

Figure 6. Hydrocassis lacustris Sharp, third instar, dorsal view. (A) Whole larva; (B) head; (C) clypeolabrum; (D) spiracular atrium; (E) tubercular pattern of thoracic and abdominal segments. Abbreviations see Figure 4.

Figure 7. Head appendages of Hydrocassis lacustris Sharp, third instar. (A) Right antenna, dorsal view; (B,C) mandibles, dorsal view; (D) left maxilla, dorsal view; (E) left maxilla, ventral view; (F) labium, dorsal view; (G) labium, ventral view. Black square indicates additional sensilla.

Figure 8. Scanning electron micrographs of Hydrocassis lacustris Sharp, first instar. (A) Head, dorsal view; (B) head, lateral view; (C) head capsule, dorsal view; (D) head appendages, dorsal view.

Figure 9. Scanning electron micrographs of Hydrocassis lacustris Sharp, third instar, dorsal view. (A) Head; (B) head capsule; (C) head appendages; (D) prothorax and mesothorax.

Figure 12. Thoracic structures of Hydrocassis species. (A) Prosternum of Hydrocassis jengi, second instar, ventral view; (B) mesothoracic leg of H. jengi, second instar, anterior view; (C) metathoracic leg of Hydrocassis lacustris, first instar, anterior view; (D) mesothoracic leg of H. lacustris, third instar, anterior view.

Figure 13. Habitats (A,B) and egg case (C) of Hydrocassis species. (A) Collecting locality of Hydrocassis lacustris Sharp, Japan: small stream near Abe-tôge, Umegashima, Aoi-ku, Shizuoka-shi, Shizuoka prefecture, altitude 1380 m, 22 June 2008; (B) collecting locality of Hydrocassis uncinata Ji et Schödl, Laos: upstream of Nam Xan River, NW Mount Phou Samsoun, Xieng Khouang province, altitude 2050 m, 13 May 2008; (C) egg case of H. lacustris Sharp, same locality as (A).