Hydrocassis uncinata Ji et Schödl, 1998

Minoshima, Yûsuke & Hayashi, Masakazu, 2011, Larval morphology of the genus Hydrocassis Fairmaire (Coleoptera: Hydrophilidae), Journal of Natural History 45 (45 - 46), pp. 2757-2784 : 2779-2783

Hydrocassis uncinata Ji et Schödl, 1998

Figures 1C , 10 , 11 , 13B

Material examined

Laos: 1 L2, 2 L3 ( SEHU), upstream of Nam Xan R., northwest Mount Phou Samsoun, Xieng Khouang province, altitude 2050 m, 19 ◦ 08.42 ′ N, 103 ◦ 47.13 ′ E, 13 May 2008, Y. Minoshima leg. (MiYu-L-08-010); 2 L3 ( SEHU), upstream of Nam Mo R., northeast Mount Phou Samsoun, Xieng Khouang province, altitude 2200 m, 19 ◦ 08.47 ′ N, 103 ◦ 48.46 ′ E, 15 May 2008, Y. Minoshima leg. (MiYu-L-08-015); 1 L2 ( SEHU), north Mount Phou Samsoun (small stream), Xieng Khouang province, altitude 2210 m, 19 ◦ 08.73 ′ N, 103 ◦ 48.24 ′ E, 15 May 2008, Y. Minoshima leg. (MiYu- L-08-016) .

Description of general morphology – third instar

Slide preparations of three specimens were examined.

Colour ( Figure 1C ). Dorsal surface of head light brown, darker in median part, with two pairs of dark brown spots on medioposterior portion; ventral surface slightly lighter than dorsal surface. Pronotum light brown, medioanterior portion darkened, dark portion spotted, rather variable in their positions; mesothoracic and metathoracic terga and abdominal segments light yellowish brown, lighter than head, slightly lighter medially and laterally; mesotergum with two dark areas on median part; dorsal sclerites and tubercles of abdominal segments somewhat darker than other abdominal portions; dorsal sclerite on abdominal segment 8 dark brown in median portion. Ventral surface of thorax and abdomen light yellowish brown, proscutum and legs darkened.

Head. Posterior 0.5 to 0.6 of head capsule bearing dense, small tooth-like cuticular projections on dorsal and lateral surfaces behind stemmata ( Figure 10B ). Nasale usually with five teeth, median tooth very small ( Figure 10C ), sometimes absent, then nasale with four teeth. Epistomal lobes projecting about as far as nasale, right lobe with numerous short spine-like cuticular projections on inner margin; left lobe with dense, fine spine-like cuticular projections on inner margin ( Figure 10C ).

Antenna. Antennomere 2 covered with fine hair-like cuticular spines on ventral and inner surfaces ( Figure 11A ). Antennomere 2 about 0.6 times as long as antennomere 1.

Abdomen. Segment 1 with three transverse rows of tubercles behind sclerites ( Figure 10E ); 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: S, L, rather L, L; third row with three large tubercles on each side, outer one projecting laterally. Arrangement of tubercles of segments 2 to 5 similar to that of segment 1 but the tubercles of first and second transverse rows somewhat larger than those in segment 1: L, rather S, L, rather L, L in first row; rather L, L, rather L, L in second row. Segment 6 similar to segments 1 to 5 but tubercles somewhat smaller than those on segments 1 to 5: rather L, S, rather L, rather L, L in first row; rather S, rather L, rather S, L in second row. Segment 7 with three transverse rows of tubercles, first row with three tubercles on each side: rather L, S, L, lateral two more closely located; second row with three tubercles: S, rather L, L, median two more closely situated; 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 0.7 times as long as Antennomere 1.

Abdomen. Abdominal transverse rows of tubercles smaller than in third instar.

Description of chaetotaxy of head – second instar

Frontale. Lateral part bearing numerous rather short secondary setae, behind FR4–6 sensilla (e.g. Figure 9B ). Each epistomal lobe with a group of seven moderately long, stout setae (gFR2), inner three slightly shorter than outer ones.

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

Mandible. With several small secondary setae on lateral part; base of mandible with five rather short secondary setae (e.g. Figure 11B, C ).

Maxilla. Stipes with 13–14 long secondary setae on outer margin; one of them very long, close to MX 4–6 (e.g. Figure 11D, E ).

Labium. Mentum with six to eight stout secondary setae in each anterolateral corner (e.g. Figure 11F, G ).

Description of chaetotaxy of head – third instar

Frontale. Each epistomal lobe with a group of seven to nine moderately long, stout setae (gFR2), median three slightly shorter than lateral ones ( Figure 10C ).

Parietale. Bearing numerous, rather short secondary sensilla, on dorsal and lateral areas (e.g. Figure 9A, B ).

Mandible ( Figure 11B, C ). with several small secondary setae on lateral part; basal part of mandible with five rather short secondary setae, three close to primary cranial articulations of mandibles.

Maxilla. Stipes with 11 long secondary setae on outer margin ( Figure 11D, E ).

Labium. Mentum with 10–11 stout secondary setae on each anterolateral corner ( Figure 11F, G ).

Habitat

Lotic water ( Figure 13B ). Larvae were found in leaf packs in the banks of a stream.

Identification

The larval specimens were collected from a mountain stream of near the top of Phou (Mount) Samsoun, northern Laos. The first author surveyed the locality for about one week and was able to collect only one species of Sperchopsini , i.e. H. uncinata . Therefore, we identified the larvae as H. uncinata . Instars were identified by sorting larvae according to the size of their head capsule and comparing the size of their head capsule with those of H. lacustris , which larvae as well as adults are almost of the same size.

Conclusion

Morphological comparison of allied genera of Hydrocassis

In this section, we compare the larval morphology among genera of Sperchopsini based on our results and published data ( Table 3). Larva of Cylomissus remains

Notes: AU, Australasia; NA, Nearctic; NT, Neotropical; NZ, New Zealand; OR, Oriental; PA, Palaearctic. See Table 1 for references.

unknown. The larvae of all genera are similar to each other in most characters, the only exception is the genus Anticura , which differs from all remaining Sperchopsini genera in the following characters: (1) nasale with two teeth; (2) inner surface of stipes with numerous stout, rather short setae; (3) dorsal sclerite of abdominal segment 8 divided into two sclerites. On the other hand, larvae of Hydrocassis are most similar to the larvae of the genus Sperchopsis and may only be distinguished by the number of setae on inner face of stipes (five in Hydrocassis , seven to eight in Sperchopsis ). In contrast, the genus Hydrocassis is easily distinguishable from Ametor by the larval morphology, although Schödl and Ji (1995) indicated a close relationship between these genera and pointed out that only the adult character clearly distinguishes the genus Hydrocassis from Ametor , i.e. the position of the corona of the aedeagus. The larva of Hydrocassis is clearly distinguishable from that of Ametor by the following characters: (1) epistomal lobes with stout setae; (2) clypeolabrum asymmetrical; (3) frontal lines not fused at base. However, all information on larval stages of Ametor are based on the widely distributed Ametor scabrosus (Horn, 1873) , which is easily distinguishable from the species of Hydrocassis by adult morphology. More extensive research on the larvae of Ametor is, therefore, necessary to solve the relationships of Hydrocassis and Ametor and confirm their separate generic states.

Larval morphology within Hydrocassis

Schödl and Ji (1995) subdivided the genus Hydrocassis into three species groups based on one adult morphological character: the shape of the parameres. The Hydrocassis species treated in the present paper belong to two of these species groups: H. lacustris and H. jengi into the H. scapulata group, H. uncinata into the H. scaphoides group. Larval morphology does not provide good characters to distinguish both species groups. The only character in which the species groups differ are the projections of abdominal segments: the projections are larger and stronger in H. uncinata than in H. jengi and H. lacustris ( Figure 1 ). However, the size and shape of these projections are more or less continuous quantitative characters and their use as diagnostic is therefore limited. Moreover, there are no good characters which clearly separate the Hydrocassis species treated in this paper from each other. Of all studied characters, only the distribution and the size of tubercles on abdominal segments show slight differences among Hydrocassis species ( Figures 4E , 6E , 10E ) and this character may therefore be useful for species identification and phylogenetic studies. The examination of more materials would be necessary to evaluate the significance of this character and confirm the homology of tubercles not only in Hydrocassis , but also in other genera of Sperchopsini .

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 4. Hydrocassis jengi Satô, second instar, dorsal view. (A) Whole larva; (B) head; (C) clypeolabrum; (D) spiracular atrium; (E) tubercular pattern of thoracic and abdominal segments. Abbreviations: T3, metathorax; A1, 2, 6, 7, abdominal segments 1, 2, 6 and 7.

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 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 10. Hydrocassis uncinata Ji et Schödl, 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 11. Head appendages of Hydrocassis uncinata Ji et Schödl, 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 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).