Acanthallagma caeruleum Williamson & Williamson, 1924

Alvarez-Alvarez, Karen Lineke, Bota-Sierra, Cornelio A. & Molineri, Carlos, 2025, Description of the last instar larva of Acanthallagma caeruleum Williamson & Williamson, 1924 (Odonata: Coenagrionidae), Zootaxa 5637 (2), pp. 374-382 : 375-380

Acanthallagma caeruleum Williamson & Williamson, 1924 ( Figs. 2–7 )

Larval diagnosis. Postero-lateral margins of head roundly projected with strong spines. Mandibular formula R 1+2 3 4 5 y a / L 1+2 3 4 5 a b. Prementum with one long premental seta at each side. Labial palp with four large setae on outer margin; inner margin crenulated; distal margin with one large inner tooth and six smaller outer denticles. Movable hook pointed, almost 0.5 times the length of external margin of palp. Caudal lamellae slightly shorter than abdomen (lamellae 0.86–0.90 the length of abdomen) with nodus and transverse suture; ratio maximum length to maximum width of lateral lamella 8.8, of dorsal lamella, 6.8.

Larval description ( Figs. 3 – 7 ). Head: two times wider than long, with posterior margin slightly concave, posterior angle with many strong spines, separated from posterior margin of eye by a marked concavity ( Fig. 3b ). Antennae: with six segments, second and third antennomeres subequal and longer than the others; fifth and sixth the shortest ( Fig. 3c ). Labrum: wider than long, rounded laterally with long thin setae dorsally and stout blunt and short setae on inner margin ( Fig. 3d ). Labium: prementum—postmentum articulation not surpassing first coxae. Prementum: subtriangular, longer than wide; ventral surface bare; dorsal surface with one large premental setae on each side of midline; lateral margin of prementum with a row of 7–8 stout setae, and a subdistal setae ( Fig. 4a ). Ligula prominent and convex, slightly crenulated with a row of minute spatulate setae; entire dorsal surface with scattered very small setae (fig.4b); Labial palp with four large acuminate setae; inner margin crenulated with a row of setae extending more than 3/4 of the length of the margin and proximal region with irregularly distributed setae; distal margin with a strong inner tooth separated by a strong concavity from six outer denticles ( Fig. 4c ); movable hook 0.36 times as long as palp (almost 0.5 times the length of external margin of palp). Hypopharynx rounded and with few long setae. Mandibles ( Fig. 4d–e ) without molar crest, with three strong long setae on outer surface near basal part. Mandibular formula: R 1+2 3 4 5 y a, L 1+2 3 4 5 a b. Maxillae: stipes distally bare; inner lobe (galea + lacinia) with four strong teeth directed medially, ventral distal tooth bifid and with a small additional tooth at base; outer lobe (palp) covered with strong setae becoming thinner toward apex ( Fig. 4f ). Thorax: pronotum with one stout spine on anterolateral corner and 2–3 stout spines on posterolateral corners; pterothorax with scattered small spines and long setae and with some strong spines near anterolateral corner ( Fig. 3b ). Wing pads parallel, reaching basal 1/4 of S4. Legs: femora sub-cylindrical, slightly bowed and with a subdistal pigmented area; 2–3 strong spines apically on outer margin; fore femur with four longitudinal rows of stout spines (two dorsal rows and two ventral ones); fore tibia with 2–3 strong spines on inner margin, with scattered long setae and with a group of stout spines (some simple other trifid); tarsi with two rows of stout setae along inner margin, and with long hair like setae along outer margin ( Fig. 5a ). Middle femur with five longitudinal rows of stout spines; middle tibia with numerous stout spines along inner margin, and with group of trifid setae apically; tarsi as in foreleg but bipectinate setae on segments 1 and 2 ( Fig. 5b ). Hind femur with four longitudinal rows of stout setae; tibia and tarsi similar to middle leg except with bipectinate setae on segments 1 and 3 ( Fig. 5c ). Tarsal claws slender pointed and slightly curved. Abdomen: mostly cylindrical, S1–8 somewhat flattened laterally, abdomen narrowing posteriorly; dorsal and ventral surface mostly bare, with some thin spiniform setae; row of stout setae on lateral margins of S1–9, along posterior margins of S5–10 dorsally ( Fig. 6a ), and S4–8 and S10 ventrally ( Fig. 6b ). Gonapophyses: lateral valvae reaching posterior margin of S10, sharply pointed and slightly diverging distally ( Fig. 6c ); with one ventral row of stout setae; 2 pairs of central valvae pale translucent and slightly shorter than lateral ones; cerci subtriangular and pointed apically ( Fig. 6d ). Caudal lamellae lanceolate, apically blunt and with nodus and transverse suture (sulcus) at 0.6 from base; basal portion with 5–6 blackish bands (pigmented tracheae), distal portion with five light brown bands. Lateral caudal lamellae: ratio length/width: 8.8; ventral margin with 29 and dorsal margin with 18 spiniform setae (stronger distally) ( Fig. 7a ). Dorsal caudal lamella: ratio length/width: 6.8; ventral margin with 20 and dorsal margin with 29 spiniform setae ( Fig. 7b ).

Measurements (mm). Total length (without caudal lamellae): 11.6. Head: max. length: 1.5; max. width: 2.8. Antennomeres: 0.38, 0.43, 0.44, 0.33, 0.20, 0.21. Prementum: max. length: 1.9; max. width: 1.5. Legs: femur 1: 1.8; femur 2: 2.0; femur 3: 2.5; tibia 1: 2.0; tibia 2: 2.5; tibia 3: 2.9. Tarsi: 1.0. Inner wingpad: max. length: 3.4. Outer wingpad: max. length: 3.1. Abdomen: total length: 7.0; S9: length: 0.7; S10: length:0.6. Cercus: length: 0.2. Gonapophyses: length: 2.0. Lateral caudal lamella: length: 6.3; max. width: 0.7. Dorsal caudal lamella, length: 6.0; width: 0.9.

Figures

FIGURE 2. Emerged adult of Acanthallagma caeruleum. a. dorsal view of the head and pronotum; b. hind wing.

FIGURE 3. Acanthallagma caeruleum, last instar larva. a. exuvia, dorsal view; b. detail of right postocular lobe and markings of the spines present on the pronotum and pterothorax; c. antennae; d. labrum (left, dorsal view; right, inner margin).

FIGURE 4. Acanthallagma caeruleum, last instar larva. a. prementum, dorsal view; b. detail of ligula. c. labial palp, dorsal view; d. right mandible, occlusal view; e. left mandible, oclusal view; f. maxillae.

FIGURE 5. Acanthallagma caeruleum, legs of last instar larva. a. front leg, dorsal view, with details of the apex of the tibia and tarsus; b. middle leg, dorsal view; c. hind leg, dorsal view.

FIGURE 6. Acanthallagma caeruleum, abdomen of last instar larva. a. dorsal view; b. ventral view; c. gonapophyses, ventral view; d. S9–10, lateral view.

FIGURE 7. Acanthallagma caeruleum, lateral view of caudal lamellae of the last larva instar. a. lateral lamella; b. dorsal lamella. Scale bar 1 mm.