Derallus angustus Sharp, 1882

Rodriguez, Georgina, Torres, Patricia L. M. & Archangelsky, Miguel, 2020, Chaetotaxy and morphometry of the head capsule and head appendages of the genus Derallus Sharp (Coleoptera: Hydrophilidae), Zootaxa 4722 (5), pp. 423-442 : 426-429

Derallus angustus Sharp, 1882

First instar larva. Chaetotaxy. Head capsule ( Figs. 5–7 ). Frontale with 42 sensilla. Six setae of gFR1 short and stout, forming an almost straight line along anterior margin, equidistant and similar to each other. Epistomal lobes with three setae (gFR2) outer two closer to each other, longer than inner one. Seta FR1 short and stout, at about midlength of frontale (one specimen has seta FR1 duplicated, Fig. 4 ); pore-like sensillum FR2 anteromesal to FR1; short seta FR5 lateral to FR2; pore-like sensillum FR4, short seta FR7 and long seta FR6 arranged in a triangle mesal to inner margin of antennal socket; short seta FR3, rather long seta FR8 and pore-like sensillum FR15 placed mesally behind nasale; six sensilla located between inner margin of antennal socket and lateral lobe of epistome, short seta FR10, long seta FR9 and pore-like sensillum FR14 forming a triangle distal to inner margin of antennal socket, pore-like sensilla FR11, FR13 and short seta FR12 forming a longitudinal line distal to seta FR9, FR12 positioned between FR13 and FR11. Parietale with 30 pairs of sensilla. Dorsal surface with five sensilla (PA1-5) forming an irregular longitudinal line on basal half of parietale, PA3 pore-like, PA1-2 and PA4-5 short setae; PA6 pore-like, basal, very close to frontal line; three setae between PA5 and antennal socket, PA12 short, and PA7-8 long; rather long seta PA13 lateral to PA12; anterolateral corner of parietale dorsally with a group of five sensilla, three long setae PA9, PA20 and PA14 arranged in a triangle, pore-like sensillum PA19 and short seta PA11 placed between PA20 and PA14. Ventral surface of parietale with two pore-like sensilla basally, PA29 close to gular sulcus and PA30, closer to lateral margin; two sensilla at midlength on lateral margin, rather short seta PA18 and pore-like sensillum PA15; a group of three sensilla at midlength between gular sulcus and lateral margin arranged in an oblique line, pore-like sensillum PA27 located between long setae PA28 and PA26; pore-like sensillum PA17 and long seta PA16 distal to PA15; three pore-like sensilla PA23-25 placed on mandibular acetabulum; anterolateral corner of parietale with long setae PA21 and PA22.

Antenna ( Fig. 8 ). With five pore-like sensilla on A1, AN1-2 dorsal and closely aggregated at basal third of segment, AN3-5 distal, AN3 on outer surface, AN5 ventral and AN4 on inner sensory appendage, inner sensory appendage apparently without spine-like projections; A2 with four distal sensilla dorsally, AN6 pore-like and subapical, short seta AN7 on membrane of outer surface basal to SE1 (AN8 and AN9 absent), and two setae on inner face, AN11 short and AN10 long, placed on a short cuticular projection; gAN on A3 with a group of at least 5 setiform sensilla; SE1 as long as A3, narrower.

Mandible ( Fig. 9 ). With six sensilla, short seta MN1 on outer margin at about basal third; minute seta MN5 on outer margin at about distal third; MN2-4 pore-like, forming an oblique line from base of distal retinaculum; minute distal pore-like sensillum (MN6) close to inner margin.

Maxilla ( Figs. 10–11 ). Cardo bearing short seta MX 1; stipes with a row of short unifid setae on inner surface ( MX 7-11) and pore-like sensillum MX 3 basal to MX 9, MX 7-9 slightly stouter than MX 10-11, outer margin of stipes with two long distal setae, MX 5-6 and two pore-like sensilla, MX 2 on basal third and MX 4 on distal third; first palpomere with four sensilla, MX 16 a short basal seta on inner margin, and MX 13-14 medium length distal setae on ventral face, MX 12 ventral and pore-like on distal margin; two pore-like sensilla at base of inner appendage, MX 17 dorsal, MX 15 ventral; inner appendage bearing a group of three setiform sensilla (gAPP), one of them long; second palpomere with two pore-like sensilla, MX 19 dorsal, on membrane connecting with following palpomere, MX 18 ventral, on outer margin, one minute seta ( MX 27) on outer surface; third palpomere bearing four distal sensilla, long seta MX 23 on outer surface and short seta MX 21 on ventral face, two pore-like sensilla also on ventral face MX 20 on outer surface and MX 22 closer to inner margin; fourth palpomere with rather long seta MX 24, subbasal on inner margin, pore-like sensillum MX 26 on outer surface, ventrally and digitiform sensillum MX 25 on outer surface, dorsally; apical portion of palpomere with several short sensilla (gMX).

Labium ( Figs. 6 , 12–13 ). Submentum with two pairs of setae on anterolateral corners, LA1 very long and LA2 short; mentum with two pairs of sensilla distally on ventral side, short setae LA3 and closer to midline pore-like sensilla LA4; dorsal face of prementum with pore-like sensilla LA8 placed basally, distally with very short setae LA9, ventrally with a pair of minute setae (LA5), long setae LA6 near midlength and pore-like subapical sensilla LA7; first palpomere with pore-like sensillum LA14 distally on membrane between first and second palpomeres and ventrally with minute basal seta LA13; second palpomere with distal pore-like sensillum LA15 on dorsal face and a group of distal short and long sensilla (gLA); ligula with two pore-like sensilla, LA12 distal, on dorsal face and LA11 at midlength on ventral face, rather long dorsal setae LA10 close to base of ligula.

Morphometry. Measurements and ratios shown in Table 1 .

Second instar larva. Chaetotaxy. Similar to third instar larva (see below) except for the following differences.

Mandible with 8–10 minute secondary setae; maxilla with 4–5 short secondary setae on outer margin of stipes. Morphometry. Measurements and ratios shown in Table 1 .

Third instar larva. Chaetotaxy. Head capsule ( Figs. 14–16 ). Frontale without secondary sensilla; FR3 proportionally longer. Parietale with two pairs of secondary setae, one dorsal short seta placed between PA8 and PA9, another very short ventral seta near PA16. Antenna ( Fig. 17 ). Without secondary sensilla, SE1 slightly shorter; sensory appendage on A1 with a pair of short spine-like projections. Mandible ( Fig. 18 ). With several (11–13) minute and very short secondary setae along outer margin between base of mandible and seta MN1; MN1 proportionally shorter. Maxilla ( Figs. 19–20 ). Stipes with 7–8 short secondary setae along outer margin. Labium ( Figs. 15 , 21–22 ). Mentum with three pairs of secondary setae; dorsally one pair short and stout setae on anterolateral corner, the other pair distal, close to midline, behind LA8; remaining pair ventral, short, subapical on outer margin.

Morphometry. Measurements and ratios shown in Table 1 .

Figures

FIGURES 5–6. Derallus angustus, head capsule, first instar larva. (5) dorsal view; (6) ventral view. Scale bar: 0.1 mm.

FIGURES 7–11. Derallus angustus, first instar larva. (7) clypeolabrum, dorsal view; (8) left antenna, dorsal view; (9) left mandible, dorsal view; (10) left maxilla, dorsal view; (11) right maxilla, ventral view. Scale bars: 0.05 mm.

FIGURES 1–4. Derallus paranensis, third instar larva. (1) habitus, dorsal view; (2) habitus, ventral view; (3) head capsule showing cuticular projections, dorsal view. Derallus angustus, first instar larva. (4) Head capsule showing duplicate FR1, dorsal view. Scale bar: 1 mm.

FIGURES 12–13. Derallus angustus, first instar larva. (12) labium, dorsal view; (13) labium, ventral view. Scale bar: 0.05 mm.

FIGURES 14–15. Derallus angustus, head capsule, third instar larva. (14) dorsal view; (15) ventral view. Scale bar: 0.1 mm.

FIGURES 16–20. Derallus angustus, third instar larva. (16) clypeolabrum, dorsal view; (17) left antenna, dorsal view; (18) left mandible, dorsal view; (19) left maxilla, dorsal view; (20) right maxilla, ventral view. Scale bars: 0.05 mm.

FIGURES 21–22. Derallus angustus, third instar larva. (21) labium, dorsal view; (22) labium, ventral view. Scale bar: 0.05 mm.