Osmylus Latreille, 1802

Matsuno, Shigetomi & Yoshitomi, Hiroyuki, 2016, Descriptions of three larvae of Osmylus species from Japan (Neuroptera: Osmylidae), with a proposed naming system for the larval sclerites, Zootaxa 4189 (2), pp. 348-366 : 349-355

The genus Osmylus Latreille, 1802

( Figs 1–14 )

Osmylus Latreille, 1802 , 289. Type species: Hemerobius maculatus Fabricius, 1787 , by monotypy. Other synonyms see Sekimoto & Yoshizawa (2011).

Description of 3rd instar larva. Cranium ( Figs 1–3 ) bulb-like shaped, well sclerotized in dorsally and laterally, smooth in surface; posterior sides gently curved and narrowing basally; ecdysial lines ( Fig. 1 ) springing form basal area of antennae, fused on center of cranium, extending basally and straightly. Setae and pores (probably campaniform sensillae) present on cranium; 4 long setae and a pair of pores or 15–20 short setae along anterior margin of labrum ( Fig. 4 ); a pair of pores existing anterior part of antennal sockets; 3 pairs very short setae and a pair of pores on frons, along ecdysial lines ( Fig. 1 ); a pair of long setae and a pair of pores between stemmata and antennal socket ( Fig. 1 ); a pair of long setae between stemmata located in lower stand ( Fig. 3 ); 2 pairs of short setae and 2 pairs of pores on vertex ( Fig. 1 ); a pair of long setae and a pair of pores on outsides of vertex ( Fig. 1 ); a pair of long setae and a pair of pores on posterior parts of stemmata ( Fig. 3 ); a pair of long setae on lateral sides in posterior part of mandible ( Fig. 3 ); 3 pairs of short setae and a pair of pores on occiput ( Fig. 1 ). Mandibles ( Figs 1– 3 ) long, curving toward outwards and upwards, without distinct teeth except for minute serrations at inside of apices, with a depigmented band near basal part. Antennae ( Figs 7–8 ) 32–45 segmented; 1st segment trapezoidal, with 2 pores; 2nd segment long, about 2.0 times as long as wide; 3rd to terminal segments cylindrical, wider than long; penultimate segment slightly longer than terminal segment, with a large sensorium at apex of lateral margin, bearing a long seta on mesal part of lateral margin, providing with a small projection in basal part of interior margin; terminal segment long, with 3 setae and a small projection at apex. Maxillary stylets ( Figs 2–3 ) long and smooth, without serra and palpi, with a depigmented band near basal part, swollen at basal portion. Intermediate maxillary elements ( Figs 2–3 ) ellipsoidal, attached to posterior margin of maxillary stylets, with 2 long setae on outside. Proximal maxillary elements ( Figs 2–3 ) similar in shape to intermediate maxillary ones, attached them, without seta. Clypeus and labrum ( Fig. 1 ) fused, attached to cranium seamlessly; front margin arcuate, somewhat horny in both sides. Labial palpi ( Figs 1–3 ) 5-segmented; first segment shortest, trapezoidal; second segment long, bearing a long seta in anterior part of dorsal and ventral surfaces; third segment shorter than second segment; forth segment longer than third segment, bearing a very short seta in anterior part of ventral surface; apical segment longest, gently tapered apically, with 2 small projections at apex. Mentum ( Fig. 2 ) subtriangular, deeply excised at center, with a pair of long setae and pore. Gula quadrate; antero-lateral angles projecting, with a pair of long setae. Cervix ( Figs 9–10 ) narrower than cranium, very elastic, provided with 2 sets of sclerites (paired D, L); D very large, T-shaped, without seta and pore, located in dorso-lateral part; L very large, with 3 branches in anterior margin, its 2 ventrally branches with 2 very short setae respectively, remaining branch with a short seta and a pore, located in ventro-lateral part.

Thorax ( Figs 9–10 ) wider than cervix and head, provided with many sclerites. Thoracic legs well developed, with many setae on each segment; an empodium present near the base of claws, with 2 setae in basal part.

Prothorax ( Figs 9–10 ) definite in shape, widely covered with large sclerite (DPc) in dorsal surface, provided with 10 sets of sclerites (DPc; paired DA1, DA2, DM, LPa, LPm, LPp, VAa, VAp, and VP); DA1 and DA2 very small, bearing a very short seta respectively, located in anterior edge, aligned transversally; DM small, bearing 2 very short setae, located in posterior part of DA2; DPc very large, widely covering dorsally, separated longitudinally, provided with 2 pairs of long and a pair of short seta, and 3 pair of pores in frontal margin, 2 pair of long/short setae in middle part, and 2 pairs of long and 2 pairs of long/short setae and 3 pairs of pores in posterior half margin, located in posterior part of DM, fused/separated with DM; LPa very large and long, sigmate, projecting dorso-anteriorly in middle, located dorsally in coxal cavity, with 4 very short setae in anterior margin; LPm small, bearing a short setae, located in posterior part of LPa; LPp very small, bearing a very short seta, located in posterior part of LPm; VAa and VAp very small, bearing a short seta respectively, located in internal part of LPa; VP very small, bearing a very short seta, located in internal part of coxal cavity.

Mesothorax ( Figs 9–10 ) wider than prothorax, elastic in anterior part, definite in posterior part, well sclerotized in surrounding part of spiracles, provided with 21 sets of sclerites (VApc; paired DAa, DAm1, DAm2+DAm3, DMa, DMp, DPa1, DPa2, DPm1, DPm2, DPp1, DPp2, LAa, LAm, LAp, LPa+LPm+LPp, VAm, VMa, VMp1, VMp2, VP); DAa small, without seta and pore, located in anterior edge; DAm1 very small, bearing a very short seta, located in posterior part of DAa; DAm2+DAm3 small, bearing 2 very short setae, located in exterior part of DAm1; DMa small, bearing 2 very short setae, located in posterior part of DAm1; DMp very small, bearing a very short seta, located in posterior part of DMa; DPa1 small, bearing a long seta, located in postero-interior part of DMp; DPa2 very large, provided with 2 long and 2/4 short setae and 2 pores, located in exterior part of DPa1; DPm1 very small, located in posterior part of DPa1, without seta; DPm2 very large, provided with a long/short setae in anterior part and 2 pairs of long setae and a pore in posterior half, located in exterior part of DPm1; DPp1 small, bearing a long/short seta, located in posterior part of DPm1; DPp2 small, bearing a long/short seta, located in exterior part of DPp1; LAa, LAm, and LAp very small, bearing a very short seta respectively, lined side by side, located in anterior margin of the segment; LPa+LPm+LPp very large and long, four-branched, its anterior upside branch bearing 3 very short setae, anterior lower side branch bearing a short seta, middle branch attached with coxal cavity, and posterior branch bearing a short and a very short seta, located dorsally in coxal cavity; VAa bearing a long seta, located in lower part of spiracle surrounded by sclerotized skin, fused with it; VAm small, bearing a short seta, located in posterior part of VAa; VApc small, without seta and pore, located in border of anterior and posterior part; VMa very small, bearing a very short seta, located in posterior part of VApc; VMp1 small, bearing long seta, located in posterior part of VAc; VMp2 small, bearing a short seta, located in exterior part of VMp1; VP small, bearing a short seta, located in interior side of coxal cavity.

Metathorax ( Figs 9–10 ) similar to mesothorax in conformation of sclerite, provided with 24 sclerites (VApc; paired DAa, DAm1, DAm2, DAm3, DAp, DMa, DMp, DPa1, DPa2, DPm1, DPm2, DPp1, DPp2, LAa, LAm, LAp, LM, LPa+LPm+LPp, VAm, VMa, VMp1, VMp2, VP); DAm2 and DAm3 separated/fused; DAp present, small, bearing a long/short seta, located in postero-exterior part of DAm3; DMa bearing a very short seta; LM present, small, without seta and pore, located in posterior part of LAa; Posterior branch of LPa+LPm+LPp bearing a short seta; VAa absent; VAm located in exterior part of VMp2.

Abdomen ( Figs 10–11 , 13–14 ) 10-segmented; spiracles present in 1st to 8th segments, its surrounding parts sclerotized, fusiform, located dorso-laterally. First abdominal segment ( Figs 11–12 ) broad, somewhat narrower than metathorax, provided with 18 sets of sclerites (paired DA1, DA2+DA3, DM1, DM2, DPa, DPp1, DPp2, DPp3, DPp4, LP, VA1, VA2, VA3, VM1, VP1, VP2, VP3, VP4); DA1 very small, bearing a very short seta, located in anterior part of segment; DA2+DA3 small, bearing 2 very short setae, located in exterior part of DA1; DM1 small, bearing a short seta, located in intero-posterior part of DA1, present/absent; DM2 small, bearing a long/short seta, located in lateral part of DM1; DPa small, without seta and pore, located in posterior part of DM1, present/ absent; DPp1 small, bearing a long/short seta, located in posterior part of DPa; DPp2 small, providing with a long and a very short seta and a pore, located in lateral part of DPp1; DPp3 very small, bearing a very short seta, located in lateral part of DPp2; DPp4 small, bearing a long/short and a very short seta, located in lateral part of DPp3; LP large, bearing a long and a long/short setae, located in postero-lateral part; VA1 very small, bearing a very short seta, located near anterior margin; VA2 very small, bearing a very short seta, located in exterior part of VA1; VA3 very small, bearing a very short seta, located in antero-lateral part of VA2; VM1 small, bearing a short seta, located in postero-interior part of VA1; VP1 small, bearing a short seta, located in posterior part of VM1; VP2 small, bearing a long seta, located in lateral part of VP1; VP3 small, bearing a short seta, located in lateral part of VP2; VP4 small, bearing a long seta, located in lateral part of VP3. Second to 5th abdominal segments ( Figs 11–12 ) similar to 1st in arrangement of sclerites, provided with 22 sets of sclerites (paired DA1, DA2, DA3, DM1, DM2, DM3, DPa, DPp1, DPp2, DPp3, DPp4, LA, LP, VA2, VA3, VM1, VM2, VM3, VP1, VP2, VP3, VP4); DA2 and DA3 independent; DM1 present/absent; DM3 very small, bearing a very short seta, located in exterior part of DM2, present/absent; LA present, small, bearing a long/short seta, located in anterior part of LP; LP bearing a long, a long/short, and a short seta; VA1 absent; VM2 and VM3 present, small, bearing a short seta respectively, located in lateral part of VM 1 in line; VP2 and VP4 bearing a long and a short seta respectively. Sixth abdominal segment ( Figs 11–12 ) similar to 5th in conformation of sclerite, provided with 19 sets of sclerites (paired DA1, DA2, DA3, DM2, DM3, DPp1, DPp2, DPp3, DPp4, LA, LP, VA2, VA3, VM1, VM3, VP1, VP2, VP3, VP4); DM1 absent; DPp2 provided with a long and a very short seta, and 2 pores; DPa and VM2 absent; VM3 present/absent. Seventh abdominal segment ( Figs 11–12 ) similar to 6th in conformation of sclerite, provided with 18 sets of sclerites (paired DA1, DA2, DA3, DM2, DPp1, DPp2, DPp3, DPp4, LA, LP, VA2, VA3, VM1, VM3, VP1, VP2, VP3, VP4); VM3 present/absent. Eighth abdominal segment ( Figs 11–12 ) similar to 7th in conformation of sclerite, provided with 9 sets of sclerites (paired DA1, DA2, DM2, DPp1+DPp2, LP, VA1, VA2, VP2, VP3+VP4); DA3, DP3, DP4, LA, VM1, VM3, and VP1 absent; DPp1+DPp2 large, provided 1–2 pores on anterior margin, 2 long and a very short setae and a pore on posterior margin; LP bearing a long, a long/short, and 2 short setae; VP3+VP4 large, bearing 2 long and a short setae. Ninth abdominal segment ( Figs 13–14 ) cylindrical, provided with 4 sets of sclerites (Dc, VPc; paired VA2, VA3); Dc very large, widely covering dorso-laterally, provided with a pair of very short setae near anterior margin, a pair of long setae and 2 pairs of pores in middle part, 1–2 long setae in each sides of latero-basal half part, 5 or 6 pairs of long setae, 1 or 2 pairs of short setae, a pair of very short seta, and 2 pairs of pores in posterior half margin; VA2 and VA3 very small, located near basal margin, with a very short seta respectively; VPc large, linguiform, arcuate in lateral sides, be-notched in posterior margin, provided with 2 pairs of setal rows, inner ones composed of 3–4 long setae, outer ones composed of 2 long setae and a pore/ a long seta in exterior margin, bearing a pair of short setae in postero-lateral parts of outer setal row. Tenth abdominal segment ( Figs 13–14 ) smaller than 9th, with 4 sets of sclerites (Dc; paired VAc, VMc, VP); Dc large, bearing 2 short setae in antero-lateral edge, sparsely covered with very short to short setae and pores in posterior half; VAc large, incised W-shaped posterior edge, provided with many short setae and pores in posterior part, widely covering ventrolaterally; VMc small, without seta and pore, located posterior part of VAc; VP small without seta and pore, located in posterior part of VMc. Membrane between VAc and VMc bearing some very short setae and pores. Hook apparatus ( Figs 13–14 ) ca. 2.0 times as long as the length of 10th segment, bearing about 10 lines of hooks on ventral surface of posterior half; hooks gradually becoming smaller basally.

Remarks. The description of the genus is based on the last (3rd) instar larvae of the three Japanese species ( O. (O.) hyalinatus , O. (O.) pryeri , and O. (P.) tessellatus ). The last instar larvae of this genus share many characters, especially the number and locations of setae and pores. There are some individual variations in the numbers of pores and setae on the sclerites.

The larval instar is easily recognized by body size, especially head width. The number of sclerites of the first instar larvae is fewer than that of the third instar. In comparison, the second instar larvae have most of the sclerites in the third instar. Because we could examine only a small number of specimens of these instar larvae, they are not described in this paper.

Figures

FIGURES 1 – 8. Head and mouth parts of Osmylus spp. 1 – 4) O. (O.) pryeri; 5 – 8) O. (O.) hyalinatus. 1) Head, dorsal view; 2) head, ventral view; 3) head, lateral view; 4 – 5) frontal edge of cranium; 6) apex of labial palpus; 7) antenna; 8) apical part of antenna.

FIGURES 9 – 10. Cervix and thorax of Osmylus (O.) hyalinatus, showing the sclerites. 9) Left in dorsal view, right in ventral view; 10) lateral view.

FIGURES 11 – 12. First to 8 th abdominal segments of Osmylus, showing the sclerites. 11) Dorsal view; 12) ventral view. These figures are modified to Osmylus (O.) hyalinatus.

FIGURES 13 – 14. Ninth and 10 th abdominal segments of Osmylus (O.) hyalinatus, showing the sclerites. 13) Dorsal view; 14) ventral view.