Hydramara argentina, (KNISCH, 1925)

Archangelsky, Miguel, Martínez Román, Nicolás Rafael & Fikáček, Martin, 2021, Larval chaetotaxy and morphology are highly homoplastic yet phylogenetically informative in Hydrobiusini water scavenger beetles (Coleoptera: Hydrophilidae), Zoological Journal of the Linnean Society 192 (2), pp. 416-416 : 416-

HYDRAMARA ARGENTINA (KNISCH, 1925)

( FIGS 1–3 , 15–34 )

Diagnosis

Larval morphology: Head capsule subquadrate; frontal lines Y-shaped, coronal line short; nasale slightly asymmetrical, with five short teeth, median tooth the shortest, right tooth projecting farther than left one; lateral lobes of epistome symmetrical, bearing seven stout setae and an inner area of strong and sharp cuticular projections; posterior tentorial grooves close to midline, anterior, close to submentum. Cervical sclerites present. Antenna short, basal antennomere the longest and widest; sensory appendage short, 0.2 × as long as third antennomere. Mandibles symmetrical, with three inner teeth at midlength, basal tooth the smallest. Maxilla with large stipes, slightly longer than palpus, inner margin with an area of short and sharp cuticular projections basally, distally bearing a strong and sharp spine; first palpomere incompletely sclerotized dorsally, bearing an inner appendage slightly longer than second palpomere, third palpomere the longest; membrane between second and third palpomeres with several short and sharp cuticular projections. Labium with submentum fused to head capsule, dorsally with sharp cuticular projections on mentum (those on disc longer), second palpomere, and membranes between prementum and first palpomere and between first and second palpomeres, projections on membranes long; mentum subtrapezoidal, wider basally; prementum subquadrate, slightly wider distally; ligula well developed, slightly longer than first palpomere; second palpomere the longest, 4.5– 5.0 × as long as first palpomere. Pronotal plate large, subrectangular, with sagittal line; those of meso- and metathorax smaller, irregularly shaped, both with sagittal line. Abdomen mostly membranous ( Figs 1–3 ), segments one to seven with one anterior pair of small dorsal plates and three pairs of small plates bearing short projections each carrying a long distal seta, two additional pairs of projections on each lateral and lateroventral margins; dorsal plate of segment eight large, sub-oval; segment nine trilobed, sclerotized dorsally. Legs well developed, five-segmented. Morphometrics. See Table 3. Chaetotaxy. gFR2 with seven stout setae projecting mediad; pore PA30 before pore PA29; A2 with three setae near SE1; seta MN1 posterior to pore MN2; pore MN4 equidistant to setae MN1 and MN5; gMX2 with six distally bifid setae; pore LA11 located at midlength of ligula.

Note: The nasale in one specimen is symmetrical ( Fig. 16 ) with median tooth the shortest and lateral teeth the longest.

Chaetotaxy

First instar larva (primary chaetotaxy): Head capsule ( Figs 17–19 ). Frontale with 30 sensilla: two very short setae on basal third, close to frontal lines (FR1); two pores (FR2) and two very short setae (FR3) on disc of frontale; three pairs of sensilla (pore FR4, short seta FR5 and long seta FR6) forming a triangle behind inner margin of antennal socket; short seta (FR7) on inner margin of antennal socket; two setae (FR10 short, FR9 long) close to inner margin of antennal socket; distal area of frontale with six pairs of sensilla, long seta (FR8) and pore (FR15) closer to midline, three pores (FR11, FR13, FR14) and very short seta (FR12) distal to inner margin of antennal socket. Nasale with eight setae (gFR1), six stout dorsal setae on anterior margin and two smaller setae ventrally, below dorsal two innermost setae of gFR1; each epistomal lobe with seven large setae projecting mediad (gFR2). Each parietale with 30 sensilla. Dorsal surface: a basal longitudinal row of four very short setae (PA1, PA2, PA4, PA5) and one pore (PA3) very close to PA2; one sub-basal pore (PA6) close to frontal lines; four long setae (PA7, PA12, PA13, PA14) arranged in a transverse row at about midlength (PA12 slightly shorter), posterior to stemmata; one pore (PA10) an two setae (PA8 very long, PA11 long) surrounding innermost distal stemma; two long setae (PA9, PA20) and one pore (PA19) on anterolateral corner of head capsule, PA9 near base of antennal socket, PA19 very close to PA20. Ventral surface with three pores (PA23, PA24, PA25) and two long setae (PA21, PA22) on anterolateral corner, close to mandibular acetabulum; two long setae (PA16, PA18) and two pores (PA15, PA30) along outer margin; one pore (PA17) close to seta PA16; two long setae (PA26, PA28) and two pores (PA27, PA29) forming a diagonal row on central area.

Antenna ( Fig. 23 ). A1 bare, with five pores, two dorsal (AN1 on basal quarter, AN2 on distal third), two lateral (AN3 apical, on outer margin, AN4 subapical, on inner margin), one ventral (AN5 apical). A2 with one dorsal pore (AN6), three distal setae on outer margin close to SE1 (AN7 and AN8 short, AN9 very short), and two distal setae on inner margin (AN11 short, AN10 very long). A3 with an apical group of at least three short setae and two very long setae (gAN). SE1 very short.

Mandible ( Fig. 24 ). One long seta on outer margin at midlength (MN1), one minute seta on outer margin at distal third (MN5), three dorsal pores at level of distal retinaculum forming a triangle (MN2, MN3, MN4), pore MN6 present, difficult to see, located subapically on inner margin.

Maxilla ( Figs 25, 26 ). Cardo with one long seta ( MX 1). Stipes with an inner row of seven setae, basal one spiniform ( MX 7), remaining six stouter, bifid (gMX2); ventrally with three pores, one close to inner margin ( MX 3), one subapical on outer margin ( MX 4) and one on disc at about midlength ( MX 2); two subapical very long setae close to pore MX 4 on outer margin ( MX 5, MX 6). MP1 dorsally with sub-basal spiniform seta ( MX 16) and one pore at base of appendage ( MX 17); ventrally two pores ( MX 15 at base of appendage, MX 12 apical on outer margin) and two long apical setae ( MX 13, MX 14); inner appendage with one long seta and three short sensilla (gAPP). MP2 with two apical pores ( MX 19 dorsal on membrane close to inner margin, MX 18 ventral, on outer margin), and one minute basal seta on outer margin ( MX 27). MP3 with two long apical setae ( MX 23 dorsal on outer margin, MX 21 ventral) and two apical ventral pores ( MX 20 on outer margin, MX 22 below seta MX 21). MP4 with)

Sperchopsis

3 L (Present Present

Limnoxenus Absent Present

Limnohydrobius Present Present

Hydrocassis Absent Present

Hydrobius Absent Present

Hydramara Absent Present

Hybogralius Absent Absent

Ametor Present Present

Continued Characters on spicules.

Table

4

Taxa Dorsal

1 LP Dorsal

on sclerite abdominal seg- ment 8

one long basal seta on inner margin ( MX 24), and two subapical pores on outer margin ( MX 25 digitiform and dorsal, MX 26 ventral); a group of several short sensilla constitute gMX1.

Labium ( Figs 19 , 31, 32 ). Submentum with two pairs of setae ( Fig. 19 ), one long close to outer corners (LA1), the other minute, on anterior corners (LA2). Mentum ventrally with one pair of subapical pores on outer margin (LA4) and two short subapical setae closer to midline (LA3). Prementum dorsally with one pair of basal pores (LA8), and one pair of minute seta-like sensilla (LA9), distally on membrane connecting with palpi and ligula; ventrally with two short setae on basal corners (LA5), two long distal setae (LA6), and two pores close to distal corners (LA7). LP1with one dorsal pore on membrane connecting with LP2 (LA14) and one minute ventral seta (LA13) basally; LP2 with one subapical pore on outer margin (LA15) and an apical group composed of one long seta and several short sensilla and pores (gLA). Ligula dorsally with a pair of long basal setae (LA10) and a pair of apical pores (LA12); ventrally with a pair of pores (LA11).

Second instar larva: Chaetotaxy more similar to the third instar than to the first. Frontale with five or six short secondary setae close to FR1. Each parietale with a row of 8–10 short secondary setae along frontal line; at least five secondary setae, one short seta close to PA9, one short seta between PA13 and PA14, one short seta behind pore PA10 (on the right side, missing on left side), one long seta near PA17, and one long seta between PA18 and PA28. Antenna. With several secondary sensilla. A1 with a patch of two (left) or three (right) setae on inner margin, surrounding pore AN4 (gAN2); A2 with a pair of basal scar-like structures on dorsal surface. Mandible. With several secondary setae arranged as follows: a subbasal patch of four or five short setae on outer margin, a row of at least 12–13 minute setae on outer margin behind MN1 and one or two minute setae between MN1 and MN4, another minute seta distal to MN4 on outer margin, this seta cannot be told apart from MN5. Maxilla. Stipes with seven long secondary setae on outer margin; seta MX 7 not bifid apically; MP1 with seta MX 16 not bifid. Labium. Mentum with a distal crown of seven stout and blunt setae on each side; a group of two or three ventral secondary long and slender setae surrounding LA3 and LA4.

Third instar larva: Head capsule ( Figs 20–22 ). Frontale with at least eight short secondary setae close to FR1; a row of 14–16 short secondary setae demarcating each missing frontal line (it is difficult to assign these setae to the frontale or to the parietale). Each parietale with at least four secondary setae, one short seta close to PA9, one short seta between PA13 and PA14, one long seta near PA17, and one long seta between PA18 and PA28. Antenna ( Figs. 15 , 27 ). With several secondary sensilla. A1 with a patch of five (left) or seven (right) setae on inner margin, surrounding pore AN4 (gAN2); A2 with two small basal pores on dorsal surface. Mandible ( Fig. 28 ). With several secondary setae arranged as follows: a sub-basal patch of six short setae on outer margin, a row of at least 13 minute setae on outer margin behind MN1 and one or two minute setae between MN1 and MN4, another minute seta distal to MN4 on outer margin, this seta cannot be told apart from MN5 (as marked in Fig. 28 ). Maxilla ( Figs 29, 30 ). Stipes with eight long secondary setae on outer margin; seta MX 7 bifid apically; MP1 with seta MX 16 bifid. Labium ( Figs 22 , 33, 34 ). Mentum with a distal crown of stout and blunt setae, illustrated specimen with eight setae on the right side and six on the left side; a group of four or five ventral secondary long and slender setae surrounding LA3 and LA4.

Figures

Figures 1–12. Hydrobiusini larvae, third instar larval habitus in dorsal, lateral and ventral view: 1–3, Hydramara argentina. 4–6, Limnohydrobius melaenus. 7–9, Sperchopsis tessellata. 10–12, Limnoxenus niger. Scale bars: 2 mm.

Figures 13–16. 13–14, cuticular projections on head capsule:13, Ametor scabrosus. 14,Sperchopsis tessellata.15,Hydramara argentina, antenna of third instar larva showing secondary setae on A1 (gAN2) and basal pores on A2 (AN6 refers to the pore that is on the antennal segment). 16, Hydramara argentina, symmetrical nasale of one atypical first instar larva.

Figures 17–22. Larva of Hydramara argentina, first instar (17–19) and third instar (20–22). 17, 20, clypeolabrum. 18, 21, head capsule in dorsal view. 19, 22, head capsule in ventral view. Scale bars: Figs 17, 20: 0.05 mm, Figs 18–19, 21–22: 0.1 mm.

Figures 23–30. Larva of Hydramara argentina, first instar (23–26) and third instar (27–30). 23, 27, antenna, dorsal view. 24, 28, right mandible, dorsal view. 25, 29, maxilla, dorsal view. 26, 30, maxilla, ventral view. Scale bars: 0.05 mm.

Figures 31–34. Larva of Hydramara argentina, first instar (31–32) and third instar (33–34). 31, 33, mentum and prementum, dorsal view. 32, 34, mentum and prementum, ventral view. Scale bars: 0.05 mm.