Cybister ( Melanectes ) brevis Aubé, 1838

Watanabe, Kohei & Hayashi, Masakazu, 2025, Description of the larva of Cybister (Melanectes) brevis Aubé, 1838 (Coleoptera, Dytiscidae, Cybistrinae), ZooKeys 1257, pp. 137-151 : 137-151

publication ID	https://doi.org/10.3897/zookeys.1257.168982
publication LSID	lsid:zoobank.org:pub:8360A184-9D76-45DD-ADAE-46C037EBA2D0
DOI	https://doi.org/10.5281/zenodo.17477534
persistent identifier	https://treatment.plazi.org/id/E0C191E6-6732-5A1E-84C1-B9E2723A38A3
treatment provided by	ZooKeys by Pensoft
scientific name	Cybister ( Melanectes ) brevis Aubé, 1838
status

Treatment

Cybister ( Melanectes) brevis Aubé, 1838 View in CoL

Figs 1–5 View Figures 1–5 , 6, 7 View Figures 6, 7 , 8–10 View Figures 8–10 , 11–14 View Figures 11–14 , 15, 16 View Figures 15, 16 , 17–19 View Figures 17–19 , 20–25 View Figures 20–25 , 26–31 View Figures 26–31 , 32–33 View Figures 32, 33 , Table 1 View Table 1

Source of material.

Descriptions were based on five instar I and two instar III specimens ( HOWP, IIM) reared ex ovo in the laboratory at the Ishikawa Insect Museum from adults collected at the following locality: Japan • Hakusan-shi , Ishikawa Prefecture; 21. VI. 2023; K. Watanabe leg. Additional specimens were collected in association with adults at the following localities: Japan • three instar I ( KWC); Awazu , Misaki-machi, Suzu-shi, Ishikawa Prefecture; 9. VII. 2023; K. Watanabe leg. ; • one instar II ( KWC); Araya-machi , Nomi-shi, Ishikawa Prefecture; 24. VI. 2021; K. Watanabe leg. ; • one instar I, two instar II ( KWC); Yawata-machi , Hakusan-shi, Ishikawa Prefecture; 21. VI. 2023; K. Watanabe leg. ; • two instar II ( KWC); Fushimi , Misaki-machi, Suzu-shi, Ishikawa Prefecture; 25. VI. 2023; K. Watanabe leg. ; • one instar III ( KWC); idem; 9. VII. 2023; K. Watanabe leg.

Diagnosis.

Larvae of C. ( M.) brevis can be distinguished from those of other Cybister species by the following combination of characteristics: egg burster spiniform; lamellae clypeales with weak longitudinal unevenness and split into several hair-like projections; lateral projections of frontoclypeus narrow; proximal article of A 2 dark brown; distal article of A 1 approximately <1.3 times longer than basal article; primary seta AN 3 absent; some individuals with almost entirely black (instar II) or dark brown (instar III) head capsule; pronotum with two dark-brown longitudinal stripes dorsally (instars II and III).

Description.

Instar I (Figs 1 View Figures 1–5 , 6 View Figures 6, 7 – 33 View Figures 32, 33 ). Color (Fig. 1 View Figures 1–5 ). Head capsule yellow-brown; frontoclypeus and parietal region internal to stemmata lighter; with several small brown maculae; stemmata brown; antennae pale yellow except for first article of A 2, apical half of third article of A 3 and A 4 dark brown; mandible pale yellow except for distal portion light yellow to red-brown, thick row of small setae on inner margin brown; maxilla pale yellow except for third article of palpomere 3 dark brown; labium pale yellow; thoracic tergites yellow-brown with several small brown maculae and pair of slightly larger brown maculae on anterior quarter of protergite; prosternal sclerites yellow-brown; base of setae on each posterior side of membranous region of meso- and metathorax brown; abdominal tergites I – VI yellow-brown with several small brown maculae; base of setae on lateromedial and ventral membranous regions brown; abdominal tergites VII – VIII yellow-brown with several small brown maculae; base of setae on ventral membranous region of abdominal tergite VII brown; legs pale yellow; urogomphus yellow-brown.

Body (Fig. 1 View Figures 1–5 ). Elongate, subcylindrical; measurements and body shape ratios are shown in Table 1 View Table 1 .

Head (Figs 6 View Figures 6, 7 – 14 View Figures 11–14 , 20 View Figures 20–25 – 27 View Figures 26–31 ). Cephalic capsule (Figs 6 View Figures 6, 7 , 7 View Figures 6, 7 , 20 View Figures 20–25 , 26 View Figures 26–31 ). Flattened, subquadrate, longer than broad; maximum width at level of anterior stemmata, constricted at level of occipital region (Fig. 20 View Figures 20–25 ), lacking temporal spiniform setae; occipital suture present; ecdysial line well marked, COL long; occipital foramen deeply emarginate ventrally (Figs 7 View Figures 6, 7 , 26 View Figures 26–31 ); tentorial pits visible slightly above middle of ventral midline (Figs 7 View Figures 6, 7 , 26 View Figures 26–31 , 27 View Figures 26–31 ); frontoclypeus subtriangular, anterior margin projected forward, divided into three well-developed projections, medial projection slightly longer than lateral projections, medial projection triangular, narrow and of same length on both sides, lateral projections triangular, slightly broader than medial projection, with inner length longer than outer length, inner margin slightly curved, notches between medial and lateral projections wide; anterolateral lobes rounded, not projecting beyond lamellae clypeales; EB present, large, spiniform (Figs 6 View Figures 6, 7 , 24 View Figures 20–25 ), near ecdysial line at level of seta PA 8; six stemmata on each side, four dorsal, two ventral. Antenna (Figs 8 View Figures 8–10 , 9 View Figures 8–10 , 25 View Figures 20–25 ). Elongate, slender, slightly longer than HW, composed of four antennomeres; A 1 and A 2 subequal in length, A 1 subdivided into two articles, distal article approximately 1.3 times longer than basal article; A 2 subdivided into three articles: first article shortest, slightly shorter than third article, second article longest; A 3 shorter than A 2, subdivided into three articles: first article shortest, slightly shorter than second article, third article longest; A 3 ’ elongate, slender, slightly shorter than A 4; A 4 shortest. Mandible (Figs 10 View Figures 8–10 , 21 View Figures 20–25 , 22 View Figures 20–25 ). Strong, falciform, broadest at base, narrowing to apex, abruptly narrowed toward apex from pore MNc; mandibular channel present. Maxilla (Figs 11 View Figures 11–14 , 12 View Figures 11–14 , 26 View Figures 26–31 ). Premaxillary lobes well developed; cardo well developed, subovate with slightly concave apex, stipes elongate, slender, subcylindrical; galea absent; PPF elongate, slender, palpomere-like; MP elongate, slender, shorter than antenna, composed of three palpomeres, MP 1 longest, MP 2 shortest; MP 1 subdivided into three subequal articles, MP 2 subdivided into two articles, distal article longer than basal article; MP 3 subdivided into three articles, first and second articles subequal in length, third article longest. Labium (Figs 13 View Figures 11–14 , 14 View Figures 11–14 , 26 View Figures 26–31 ). Prementum broader than long, not sclerotized ventromedially, anterodorsal margin well projected forward into rounded median process; LP approximately half as long as MP, composed of two palpomeres; LP 1 longer than LP 2; LP 1 subdivided into two articles subequal in length; LP 2 subdivided into two articles, distal article longer than basal article.

Thorax (Figs 1 View Figures 1–5 , 15 View Figures 15, 16 , 16 View Figures 15, 16 , 28–31 View Figures 26–31 ). Pro-, meso-, and metanotum convex, with subequal width; protergite longer than broad, twice as long as mesotergite, subrectangular, lateral margins emarginate at about mid-length, anterior and posterior margins straight; meso- and metatergite small, broader than long, subequal in length, subtrapezoidal, posterior margin emarginate medially; sagittal line present on all tergites; sternum of prothorax membranous except for one pair of small subtriangular sclerites, sterna of meso- and metathorax membranous; spiracles absent. Legs (Figs 15 View Figures 15, 16 , 16 View Figures 15, 16 , 28–31 View Figures 26–31 ). Long, composed of six segments, L 1 shortest, L 3 longest; CO, FE, TI, and TA subcylindrical, elongate, slender; TR short, divided into two parts by an annulus; PT with two long, curved claws; TA of L 1 with apically multifid setae forming a dense patch (cleaning device), these setae larger and flat on posteroventral region (Figs 28 View Figures 26–31 , 29 View Figures 26–31 ), smaller on anteroventral region (Figs 30 View Figures 26–31 , 31 View Figures 26–31 ).

Abdomen (Figs 1 View Figures 1–5 , 17–19 View Figures 17–19 , 32 View Figures 32, 33 , 33 View Figures 32, 33 ). Eight-segmented; segments I – VI subequal in length, mostly membranous with a small tergite on anterodorsal region, tergites I – VI subrectangular, without anterior carina, sagittal line present; sterna of segments I – VI membranous; segment VII narrower, subtrapezoidal, without anterior carina, sagittal line absent, fully sclerotized except ventrally; segments I – VII without spiracles; segment VIII longest and narrowest, fully sclerotized except around anus. Urogomphus (Figs 19 View Figures 17–19 , 32 View Figures 32, 33 , 33 View Figures 32, 33 ). Strongly reduced in length, slightly broader than long, comprised of one urogomphomere.

Chaetotaxy. Similar to that of generalized Cybister larva ( Alarie et al. 2011; Alarie and Michat 2023; Watanabe and Hayashi 2024) with the following remarks: lamellae clypeales with weak longitudinal unevenness and split into several hair-like projections (Fig. 23 View Figures 20–25 ); setae PA 1–3 apically rounded (Fig. 6 View Figures 6, 7 ); seta FR 10 broad (Fig. 6 View Figures 6, 7 ); seta AN 3 absent (Figs 9 View Figures 8–10 , 25 View Figures 20–25 ); row of short setae present on outer margin of mandible, around pore MNc (Fig. 10 View Figures 8–10 ); setae MX 11 and MX 14 multi-branched (Figs 11 View Figures 11–14 , 12 View Figures 11–14 ); seta TR 4 not multi-branched (Fig. 15 View Figures 15, 16 ); setae AB 1, AB 12, and AB 13 apically rounded (Figs 17 View Figures 17–19 , 18 View Figures 17–19 ); seta AB 4 long (Fig. 17 View Figures 17–19 ).

Instar II (Figs 2 View Figures 1–5 , 3 View Figures 1–5 ). As for instar I except as follows:

Color (Figs 2 View Figures 1–5 , 3 View Figures 1–5 ). Head capsule varies among individuals, ranging from yellow-brown with numerous small brown maculae (Fig. 2 View Figures 1–5 ) to almost entirely blackened (except for frontoclypeal anterior projections and area posterior to occipital suture) (Fig. 3 View Figures 1–5 ); thoracic tergites and abdominal tergites I – VI with two brown to dark brown longitudinal stripes; membranous region of pro-, meso-, metanotum, and abdominal segments I – VI gray-brown, paler on both sides; abdominal tergite VII light-brown to gray-brown on both sides, yellow-brown in center with several small brown maculae; abdominal tergite VIII light brown to gray-brown with several small brown maculae.

Body. Measurements and body shape ratios are shown in Table 1 View Table 1 .

Head. EB absent; HW / OCW = 2.00–2.10. A / HW = 1.06–1.08; A 2 / A 1 = 0.94–0.95; A 3 / A 1 = 0.60–0.67. MP 3 / MP 2 = 1.31–1.37.

Chaetotax y. Identification of secondary setae was difficult due to the large number of additional setae.

Instar III (Figs 4 View Figures 1–5 , 5 View Figures 1–5 ). As for instar II except as follows:

Color (Figs 4 View Figures 1–5 , 5 View Figures 1–5 ). Head capsule varies among individuals, ranging from yellow-brown with numerous small brown maculae (Fig. 4 View Figures 1–5 ) to almost dark brown (Fig. 5 View Figures 1–5 ); thoracic tergites and abdominal tergites I – VI with two dark-brown longitudinal stripes; membranous region of pro-, meso-, metanotum, and abdominal segments I – VI gray-brown (Fig. 4 View Figures 1–5 ) to dark-gray-brown (Fig. 5 View Figures 1–5 ), paler on both sides; abdominal tergite VII yellow-brown to gray-brown with two dark-brown stripes, and several small brown maculae; abdominal tergite VIII yellow-brown (Fig. 4 View Figures 1–5 ) to brown (Fig. 5 View Figures 1–5 ) with several small brown maculae.