Micrathyria almeidai Santos, 1945

Dias-Oliveira, Tomás Matheus, Santos, Jean Carlos, Urso-Guimarães, Maria Virginia & Vilela, Diogo Silva, 2025, The F- 0 exuvia of Micrathyria almeidai Santos, 1945 (Odonata: Libellulidae), Zootaxa 5646 (3), pp. 344-350 : 345-347

F-0 exuvia of Micrathyria almeidai Santos, 1945

Figs. 1−3

Material examined. 1 F-0 exuvia (♂ emerged in laboratory), BRAZIL, São Paulo state, Serra do Japi Municipal Biological Reserve , eucalyptus pond (23°14’17”S 46°56’26”W, 1053m asl), collected and emerged between Nov– Dec 2024, T. M. Dias-Oliveira leg., CBVS .

Description. Exuvia small, brown with darker patterns on head and dorsal abdomen ( Fig. 1a ); femora light brown with dark bands; posterolateral spines on S8−9; S10 sunken into S9; caudal appendages dark brown with acute apex.

Head. Roughly rectangular, twice as wide as long, wider than thorax, slightly narrower than abdomen ( Fig. 1a ). Antenna ( Fig. 1b ) long and filiform, 7-segmented; segments light-brown colored; scape and pedicel stout, wider than the remaining segments; 3rd antennomere longest; proportional lengths of antennomeres: 0.38, 0.51, 1, 0.7, 0.75, 0.9, and 0.96. Compound eyes rounded and laterally prominent ( Fig. 1a ). Mandibular formula R 1234 y abd / L 1234 0 abb’; tooth size ratio: b>a>b’ in left mandible, d>b>a in right mandible ( Fig. 2a ). Maxilla (galeolacinia and maxillary palp): galeolacinia with seven teeth: three dorsal and four ventral teeth of different sizes and robustness; maxillary palp slightly shorter than galeolacinia, terminating in a large, blunt spine; both galeolacinia and maxillary palp bear abundant, long setation ( Fig. 2b ). Prementum 0.75 as wide as long, widely concave; 13 (left) and 11 (right) large premental setae, additional smaller setae on each side of the midline; ligula moderately developed, anterior margin finely crenulated with three medial spines on apex, middle one shorter; row of>10 spiniform setae of different sizes on each side ( Fig. 1c ). Labial palp roughly triangular, with 7 marked crenations on apical margin, each one bearing 4–6 setae, ventral setae largest; 10 palpal setae on dorsal margin; ventral margin finely crenulated, bearing>20 small setae, of which 15 are longer setae; internal surface of palp with darker spots near apical margin, basal patch of 11 small spines ( Fig. 1d ).

Thorax. Prothorax and pterothorax narrower than head; prothorax light brown with a large dark brown spot covering most of dorsal portion; anterior margin and lateral portion with a patch of small setae ( Fig. 1a ). Pterothorax light brown, with darker lateral bands covered with minute spines ( Fig. 1a ). Legs light brown with darker bands (all tarsi missing); femora with dorsal and ventral rows of setae of different sizes; long setae more abundant ( Fig. 1a ).

Abdomen. S1−5 light brown with scattered pattern of darker spots; S6−10 dark brown with darker spots on each side of midline; widest portion at S6−7, narrowing towards S10; covered with minute setae along the dorsal portion, and a row of setae on posterior margin of each segment; posterolateral spines present on S8−9, sharply pointed, those on S8 less than half the length of those on S9. S10 short, sunken into S9 ( Fig. 1a ). Caudal appendages ( Fig. 1e ) dark brown, long, sharply pointed; epiproct nearly triangular, with two lateral dark stripes, bearing two small apical setae; paraprocts pyramidal, 0.30 longer than epiproct, bearing a row of long setae; cerci shortest of the anal appendages, 0.65 length of epiproct.

Measurements. AL: 9.5; MWA: 5.1; TL: 15.4; Head: 2.38; Head width: 4.7; AWP: 4.2; PWP: 3.44; S8 spine:

0.31; S9 spine: 0.69; AnP: 1.57.

Diagnosis. The exuvia of M. almeidai belongs to the second group proposed by Souza & Costa (2002), according to the number of palpal setae (n = 10) and dark ventral spots on the abdomen. In the key in Souza & Costa (2002), the exuvia of M. almeidai falls into the same couplet as M. hypodidyma Calvert, 1906 , sharing two rows of dorsal dark spots on S5–9. Of these species, M. almeidai can be separated by the following character combination ( M. hypodidyma in parenthesis): 10 palpal setae (11); abdomen and total length, 9.5 and 15.4, respectively (11 and 19); cerci parallel to each other, measuring 0.65 length of epiproct (cerci divergent, measuring 0.75 length of epiproct) ( Fig. 1 ). Santos (1968) did not provide any information on the dental formula for M. hypodidyma ; hence, we could not perform a proper comparison of these structures with the exuvia of M. almeidai . However, two other species ( M. borgmeieri Santos, 1947 , and M. ocellata Martin, 1897 ) also key to M. almeidai in the key of Souza & Costa (2002), sharing the following characteristics, based on descriptions by Assis & Costa (1994): epiproct with two spines; left mandible with two molars (a,b) if with three, molar (c) is absent. Of these species, the exuvia of M. almeidai can be separated by the following character combination ( M. borgmeieri and M. ocellata in parenthesis): total length 15.4 ( M. borgmeieri : 16.95; M. ocellata : 19); 10 palpal setae (11 in M. borgmeieri and M. ocellata ); left mandible formula: 1234 0 abb’ ( M. borgmeieri : 1234 0 ab; M. ocellata : 1234 0 abd) ( Fig. 2a ); paraprocts 0.30 longer than epiproct (0.45 longer in M. borgmeieri ; 0.40 longer in M. ocellata ).

On the other hand, the imago of M. almeidai differs greatly from that of M. hypodidyma , M. borgmeieri , and M. ocellata adults ( Santos 1945; Costa et al. 2002). The combination of cerci and hamule structures of these three species allows for their robust separation from M. almeidai ( Costa et al. 2002) ( Fig. 3 ). However, M. stawiarskii Santos, 1953 , is morphologically close to M. almeidai with respect to hamuli and cerci. The two species can be separated by the following character combinations ( M. stawiarskii in parentheses): cerci not constricted along its midlength, tips convergent or parallel (cerci strangled at midlength, tips divergent; see Costa et al. 2002, figs. 9 and 16); vesica spermalis ( Fig. 3c , above) with a narrow dorsal cleft, forming a truncated and roughly squared lobe (vesica spermalis with a broad dorsal cleft, forming a long, digitiform lobe; Fig. 3c , below).

Habitat and biology. The study area is characterized by primary and secondary Atlantic Forest vegetation with diverse aquatic habitats, such as streams, waterfalls, and ponds. The larva was observed in an artificial pond surrounded by a secondary Atlantic rainforest and mature eucalyptus plantation ( Fig. 4 ). The specimen was associated with the marginal zones of the ponds, characterized by muddy sediment with the accumulation of clay, silt, and organic matter at the bottom of the water body. This marginal zone also supports numerous amphibious, emergent, and submerged macrophytes. Adult specimens were not observed.

Figures

FIGURE 1. F-0 exuvia of Micrathyria almeidai: (a) dorsal view of habitus; (b) antenna; (c) dorsal view of prementum; (d) anal pyramid; (e) left labial palp.

FIGURE 2. F-0 exuvia of Micrathyria almeidai: (a) right and left mandibles; (b) galeolacinia.

FIGURE 3. The imago of Micrathyria almeidai: (a) left view of male habitus; (b) lateral view of anal appendages; (c) above— vesica spermalis of M. almeidai, below—vesica spermalis of M. stawiarskii (adapted from Santos 1953).

FIGURE 4. Habitat of Micrathyria almeidai at the Serra do Japi Municipal Biological Reserve.