Pelosoma sp. (Archangelsky, 1997)

Rodriguez, Georgina & Archangelsky, Miguel, 2023, Larval chaetotaxy and morphometry of Megasternini: Cercyon (Paracercyon) Seidlitz, Cryptopleurum Mulsant and Pelosoma Mulsant (Coleoptera: Hydrophilidae), Zootaxa 5318 (1), pp. 45-66 : 56-60

Pelosoma sp. first-instar larva chaetotaxy

For general morphological characters of Pelosoma larvae see Archangelsky (1997).

Morphometry. Measurements and ratios in Table 1 .

Primary chaetotaxy. Head capsule ( Figs. 48–50 ). Frontale with 14 pairs of sensilla: two rather long setae on basal quarter, close to frontal lines (FR1); two pores (FR2) and two setae (FR3, short) distal to FR1, close to midline; one pore (FR4) distal to FR3, near inner margin of antennal sockets; two pairs of setae laterad to FR3 (FR5 short and FR6 long); one pair of pores (FR15) posterior to central area of nasale, behind egg bursters; five pairs of sensilla distal to mesal margin of antennal socket, three setae (FR8 and FR9 long, FR10 minute) and two pores (FR13, FR14); one short seta (FR12) and a pore (FR11) located anterodistal to the group form by FR8-10 and FR13-14; nasale with gFR1 bearing six setae, four dorsal short and stout and a pair of smaller setae inserted ventrally. Epistomal lobes lacking sensilla, therefore gFR2 absent. Seta FR7 absent. Each parietale with 30 sensilla: dorsal surface with a basal longitudinal row of four minute setae (PA1, PA2, PA4, PA5) and one pore (PA3) located closer to frontal line; basal pore (PA6) almost touching frontal line; seta PA7 long, distal to PA5; setae PA12, PA13 and PA14 on lateral margin at about midlength, distal one short, remaining two long, not closely grouped; seta PA8 very long, close to frontal line, behind antennal socket; pore PA10 and short seta PA11 lateral to seta PA8; seta PA9 long, lateral to antennal socket; pore PA19 and short seta PA20 on anterolateral corner of head capsule. Ventral surface with three pores (PA23, PA24, PA25) and two setae (PA21 long, PA22 short) on anterolateral corner, close to mandibular acetabulum; lateral margin with pore PA15 at about midlength and long seta PA18 on basal third; a transverse row of two pores (PA27 and PA17) and two setae (PA26 short, PA16 long) at distal third, PA26 located between PA17 and PA27, PA27 closer to base of submentum; long seta PA28 behind pore PA27; basally two pores, PA29 closer to midline and slightly posterior to PA30.

Antenna ( Fig. 51 ). A1 bare, with five pores, four dorsal (AN1 on basal third, AN2 subapical, AN3 subapical on outer margin, AN4 subapical on inner margin), remaining pore AN5 ventral and subapical. A2 with two dorsal pores, distal one (AN6) and subbasal one additional (■), and four setae on membrane connecting with A3, two on inner margin (AN10 rather long and AN11 very short), two on outer margin (AN8 and AN7 very short). A3 with a group of at least five sensilla (gAN).

Mandibles ( Figs. 52–53 ). Both mandibles with five primary sensilla: one short seta on outer margin at basal third (MN1), one minute seta (MN5) on outer margin at distal third in right mandible (closer to apex in left mandible), three dorsal pores (MN2, MN3, MN4) forming an oblique row at about midlength, MN3 closer to inner margin, more basal, MN4 on outer margin, more distal; pore MN6 not found.

Maxilla ( Figs. 54–55 ). Cardo with one short seta ( MX 1). Stipes dorsally with a row of nine short and stout setae along inner margin; basal seta of that row likely homologous to MX 7, simple, remaining setae forming gMX2, basal five bifid apically; ventral face with three pores, one on basal third ( MX 2), one at distal third close to inner margin ( MX 3) and one on outer margin ( MX 4), two setae distal to pore MX 4 ( MX 5 longer, MX 6 shorter). MP1 dorsally with one basal spiniform seta ( MX 16), pore MX 17 apparently absent; ventrally with two subapical setae ( MX 13 very long, MX 14 shorter) and two pores ( MX 12 on outer margin, MX 15 on inner margin at base of gAPP); inner appendage reduced, with several sensilla of different lengths (gAPP). MP2 with two apical pores, one ventral near outer margin ( MX 18) and one dorsal near inner margin ( MX 19); one basal minute seta ( MX 27) on outer margin. MP3 with two setae and two pores, one very long seta ( MX 23) dorsal, on outer margin, the other short ( MX 21) ventral on inner margin; both pores on ventral surface, one ( MX 22) close to seta MX 21, the other ( MX 20) on outer margin. MP4 with one short basal seta dorsally ( MX 24) and two dorsal pores, one digitiform and central ( MX 25), the other close to outer margin ( MX 26); a group of seven or eight very short sensilla constitute gMX.

Labium ( Figs. 49 , 56 ). Submentum with two pairs of setae ( Fig. 49 ), basal one rather long (LA1), the other minute, on anterior margin (LA2). Mentum ventrally with one pair of long setae (LA3) and one pair of lateral pores (LA4). Prementum ventrally with two pairs of setae (LA6 very long, LA5 minute) and one pair of lateral pores (LA7), dorsally pores LA8 absent; sensilla associated with ligula absent (LA9–11) except for one pair of pores (LA12?, close to base of palpi). LP1 ventrally with one minute seta (LA13, ventral) and one distal pore (LA14, on membrane connecting with LP2); LP2 with one subapical pore on outer face (LA15) and a group of six or seven short sensilla that constitute gLA.

Figures

FIGURES 48–53. Pelosoma sp., first instar larva. (48) head capsule, dorsal view; (49) head capsule, ventral view; (50) clypeolabrum, dorsal view; (51) antenna, dorsal view; (52) mandible, dorsal view; (53) mandible, dorsal view. Scale bars, Figs. 48–49: 0.05 mm; Figs. 50–53: 0.025 mm.

FIGURES 54–56. Pelosoma sp., first instar larva. (54) right maxilla, ventral view; (55) right maxilla, dorsal view; (56) labium, ventral view. Scale bars: 0.025 mm.