Heteragrion Selys, 1862

Vilela, Diogo Silva, Lencioni, Frederico A. A., Bota-Sierra, Cornelio A., Ware, Jessica L. & Bispo, Pitágoras C., 2023, Taxonomic revision of the Neotropical genus Heteragrion Selys, 1862 (Zygoptera: Heteragrionidae): male morphology, new species and illustrated key, Zootaxa 5356 (1), pp. 1-96 : 8-18

Heteragrion Selys, 1862

Type species: Heteragrion flavovittatum Selys, 1862: 18 , by original designation.

Other species included: Heteragrion aequatoriale Selys, 1886 ; H. albifrons Ris, 1918 ; H. alienum Williamson, 1919 ; H. angustipenne Selys, 1886 ; H. archon De Marmels, 2008 ; H. aurantiacum Selys, 1862 ; H. azulum Dunkle, 1989 ; H. bariai De Marmels, 1989 ; H. beschkii Hagen in Selys, 1862; H. bickorum Daigle, 2005 ; H. breweri De Marmels, 1989 ; H. brianmayi Lencioni, 2013 ; H. calafatiensis Mendoza-Penagos, Juen & Vilela, 2022 ; H. calendulum Williamson, 1919 ; H. cauei Ávila-Jr., Lencioni & Carneiro, 2017; H. chlorotaeniatum De Marmels, 1989 ; H. chrysops Hagen in Selys, 1862; H. cinnamomeum Selys, 1862 ; H. consors Hagen in Selys, 1862; H. cooki Daigle & Tennessen, 2000 ; H. corderoi sp. nov.; H. cyane Machado & Souza, 2014 ; H. demarmelsi Stand-Pérez, Bota-Sierra & Pérez-Gutiérrez, 2019 ; H. denisye Vilela, Koroiva & Guillermo-Ferreira, 2019 ; H. dorsale Selys, 1862 ; H. eboratum Donnelly, 1965 ; H.erythrogastrum Selys, 1886 ; H. flavidorsum Calvert, 1909 ; H. freddiemercuryi Lencioni, 2013 ; H. gorbi Cezário & Guillermo-Ferreira, 2021 ; H. gracile Machado, 2006 ; H. ictericum Williamson, 1919 ; H. icterops Selys, 1862 ; H. inca Calvert, 1909 ; H. itacolomii Ávila-Jr., Lencioni & Carneiro, 2020; H. johndeaconi Lencioni, 2013 ; H. lencionii Vilela, Farias & Santos, 2021 ; H. luizfelipei Machado, 2006 ; H. majus Selys, 1886 ; H. makiritare De Marmels, 2004 ; H. mantiqueirae Machado, 2006 ; H. mitratum Williamson, 1919 H. muryense Costa & Santos, 2000; H. obsoletum Selys, 1886 ; H. ochraceum Hagen in Selys, 1862; H. ovatum Selys, 1862 ; H. palmichale Hartung, 2002 ; H. pemon De Marmels, 1987 ; H. peregrinum Williamson, 1919 ; H. petiense Machado, 1988 ; H. rogertaylori Lencioni, 2013 ; H. roquei Vilela, Rodrigues & Lencioni, 2022 ; H. rubrifulvum Donnelly, 1992 ; H. silvarum Sj ̂stedt, 1918; H. simulatum Williamson, 1919 ; H. tatama Bota-Sierra & Novelo-Gutiérrez, 2017 ; H. thais Machado, 2015 ; H. tiradentense Machado & Bedê, 2006 ; H. triangulare Hagen in Selys, 1862; H. tricellulare Calvert, 1901 ; H. valgum Donnelly, 1992 . From now on, authors’ names and publication dates will be omitted.

Generic characterization and diagnosis (distinct features from other heteragrionids in squared brackets). Medium to large (36–60mm) heteragrionids [ Dimeragrion Calvert, 1913 30–52mm; Heteropodagrion Selys, 1885 and Oxystigma 35–50mm]. Head varying from entirely black, black dorsally and yellow ventrally, reddish, and irregular patterns of black, blue, grey and orange [black and blue in Oxystigma ; brown to black with pale details in Dimeragrion and Heteropodagrion ]; angulated frons (shared with other heteragrionids). Posterolateral margins and hind lobe of prothorax rounded (shared with Oxystigma ). Pterothorax often bearing a black humeral stripe; overall coloration black/brown, with pale and vivid yellow/orange areas in most species, others with shades of grey and blue [ Dimeragrion with black and pale colors, bearing some dorsal pruinescence in some species; Heteropodagrion with reddish tones]; hind femur almost reaching S2 [reaching mid S 2 in Dimeragrion , Heteropodagrion and Oxystigma ]; no accessory veins basal or distal to CuP [with 1 or more basal veins in Dimeragrion ]; CuP closer to antenodal 2 than to 1 [closer to antenodal 1 in Heteropodagrion ; closer to antenodal 1 or midway between 1 and 2 in Oxystigma ]; two cells between quadrangle and vein descending from subnodus in HW discoidal field [1 cell in Oxystigma ; 1 or 2 in Heteropodagrion ]; RP 3 recessed at subnodus or proximal to nodus [recessed well before subnodus in Dimeragrion and Heteropodagrion ; at subnodus in Oxystigma ]. Abdomen with no tubercles in ventral S1 [a pair of tubercles in Dimeragrion ]; in most species yellow/orange, dark brown or black dorsally with pale apical rings, S8–10 largely orange, with some species presenting lively red or blue/black colors [largely black in Oxystigma ; bearing pruinosity in the last segments in Dimeragrion ]; distal segment of genital ligula with lateral flagella, lacking inner fold [well-developed inner fold in Dimeragrion and Heteropodagrion ]. Cerci elongated, forcipate or spear-like, robust compared to the length of S10, with a well-developed medial lobe [poorly developed on Heteropodagrion ]; Group B species with well-developed paraprocts, which vary in size and shape.

These features have been described and compiled based on previous studies by Geijskes (1976), De Marmels (1987, 1989), von Ellenrieder & Garrison (2007), Garrison et al. (2010), Lencioni (2013), and Garrison (2014).

Morphological comments

The taxonomic diversity of Heteragrion is evident when examining its representatives, that stands out among other members of the family ( Williamson 1919; Garrison et al. 2010; Lencioni 2013; Stand-Pérez et al. 2019). Species delimitation in this genus is mostly based on the morphology of the male anal appendages, as knowledge of female structures is still limited and requires further extensive study, although recent publications have made significant progress on this topic ( Bota-Sierra & Novelo-Gutiérrez 2017; Stand-Pérez et al. 2019; Vilela et al. 2019a). When comparing the two groups of species in Heteragrion (A and B), it is possible to observe some distinct differences in their appendages: 1) in Group A species, the cerci have a more truncate and forcipate aspect (“ en crochets ”, as stated by Selys 1862), with basal dilatations and broad plates (see Figs. 1–4 for comparisons between the groups); and 2) in Group B species, the cerci are more slender, spear-like and often with acute tips. However, there are some exceptions. For instance, H. aurantiacum ( Figs. 12f–i ), a Group A species, has the basal portion of cercus poorly expanded, in contrast to other species from the same group, like H. brianmayi ( Fig. 18d ) or H. cauei ( Fig. 21d ). Similarly, H. archon ( Fig. 11c ) and H. palmichale ( Fig. 53c ), both Group B species, have broad and downward curved cercus, standing out not only from other Group B species, but from all congeners.

The cercus in Heteragrion (see also Lencioni 2013 for further images on different angles) can be divided into three main portions ( Figs. 1a–b , 2a–h , 3a–f ):

(i) the basal portion (BP), which is the part of the cercus attached to S10, displays a wide range of morphological variations among the different species. They can be compact ( Figs. 2e–f ); bear many degrees of convexities ( Figs. 10f , 14e, g ) or hollow concavities ( Figs. 15c , 25e , 52e ); tubercles or apophyses ( Figs. 4b–c ); or unique ventral branches ( H. muryense , Figs. 51c–d ). The structural features of the BP are far more diversified in shape and size on Group A species, whereas Group B species have usually compact BPs, lacking any expanded concavities in this area. On the other hand, BP convexities (as seen in Figs. 10f , 14e, g ) are a Group B feature. It is important to notice the difference between the convexities present in some Group B species and the ventral tubercle (or apophysis, Figs. 4b–c ) present in some Group A species: whereas the convexities are expanded medially on the medial margin of the BP, the tubercles are extended downwards, being restricted to that ventral area.

(ii) the medial portion (MP), whose extension is delimited by the size and development of the medial lobe (ML, Fig. 1a ) and the extension of the toothed carina ( Fig. 1b ), bears the most important character-delimiting species on the genus. The ML is a more complex structure in Group A than in Group B species. Some Group A species have the ML composed of a lower plate, an upper plate, and a carina that extends between them, in a “two-story” structure ( Figs. 2a–d ). Other species of the same group have more simple ML structures, bearing a medial toothed carina (elevated carina in H. cooki , Fig. 26c ), dividing the plate and reaching or not its apex ( Figs. 3a–c ). The apex is also a structure that varies in shape and size, being squared ( Fig. 63c , 65c ), rounded ( Fig. 28c , 45d ), bilobate ( Fig. 30c ) or undulate ( Figs. 37c–d ). On species from Group B, the medial portion (MP) features a toothed ridge, located immediately above the ML ( Figs. 1b , 2g –h , 3d–f ). In some species, the toothed ridge is robust, bearing strong teeth and covering part of the ML in dorsal and dorsolateral views ( Figs. 2g –h ). In other species, the ridge bears only small teeth, not covering the ML in any view ( Figs. 9e , 20e , 32c–d ). Or the ML is free of any dividing ridges, the plate entire or smooth ( Figs. 2e–h ). In some cases, a row of small teeth on the ML do not form a ridge ( Fig. 62d ). In contrast, all Group A species bear a strong ridge dividing the ML, in most cases at its middle.

(iii) the apical portion (AP) is delimited from the MP by a junction that may be in different shapes: angled ( Fig. 14d–e ), rounded ( Fig. 14g ), or nearly straight ( Fig. 19c ). Where this junction is not well delimited at the base of ML, as seen in H. calafatiensis ( Fig. 19 ), the MP-AP border is delimited by the apical end of the toothed ridge (i.e., apical tooth, Fig. 19c ). AP varies greatly in length, being long, as in H. albifrons ( Figs. 8c–d ) and H. consors ( Fig. 25c ), or very short, as in H. archon ( Fig. 11c ), H. palmichale ( Fig. 53c ) and H. calendulum ( Fig. 20e ). In species with long AP portions, it is quite common for these structures to include a longitudinal depression ( Fig. 31c ). In medial view, the AP does not bear any morphological character important in taxonomic distinction. Instead, it is invariably a slightly concave structure bearing no ridges or carinas; those are confined to the upper margin ( Figs. 14e , 16e ).

Intraspecific variation and species delimitation

Especially for species in which we could examine a large series of specimens, a wide range of variation in terms of color and morphology were observed ( Figs. 5 , 12 , 42 , 60 ). As discussed by Bota-Sierra & Novelo-Gutiérrez (2017), color and morphological variation are known and well documented for only a few species of the genus, and based on what we could observe among the examined material and literature, this variability has been recorded for only a few species due to inadequate sampling and, in some cases, poor preservation of deposited specimens.

Some boundaries between species are difficult to delimit, mainly because many of them are represented by few individuals, making difficult the analysis of intra- and interspecific variability. For example, similar species such as H. ictericum and H. pemon ; H. palmichale and H. archon ; H. rogertaylori and H. thais are morphologically close, and new synonymies may be feasible pending studies on a molecular level or further morphological assessment with more specimens. Thus, we can assume that the intraspecific variation of nearly half of the Heteragrion species is unknown or poorly known, and this can lead us to misinterpret variations, causing species to be described as new that later can have their names synonymized.

In this study, we treat these species as valid and consider the combination of characters provided by the original authors to separate morphologically close taxa.

Several Heteragrion species (14, to be accurate) have their conservation status assessed as Data Deficient in the IUCN Red List, mainly due to the paucity of specimens known and recent specimens lacking (see species accounts). These species total nearly 23% of the known species, and this percentage may grow even more if we add recently described species (i.e., in the last 30 years) based on small series collected in one or two localities, such as H. muryense , H. gracile , H. mantiqueirae , H. freddiemercuryi , H. brianmayi , H. johndeaconi , H. cyane , H. thais , H. denisye , and H. roquei .

Distribution

This genus is widespread in the Neotropical region, being found from Central Mexico to Southern Brazil and Northeastern Argentina ( Fig. 6 ). As discussed in the previous section, the distributional data for most species is probably still inadequate, but even with this data deficit we can spot a difference in distribution between the two distinct groups of species.

Group B species ( Fig. 6 , red dots) are mostly found in the Andean region, Central America, and Mexico, whereas Group A species ( Fig. 6 , green dots) are found mostly in Brazil (from North to South), but also being recorded in Venezuela, Ecuador and in the southern Brazilian border with Argentina. There is a “common area”, where species from both groups can be found, that ranges from southern Venezuela to the Brazilian state of Mato Grosso, comprising, therefore most of the Brazilian and Venezuelan Amazon Basin.

Identification key

Key to male Heteragrion species ( H. dorsale , H. ochraceum and H. obsoletum omitted due to lack of information on types, and taxonomic uncertainty)

Important note: This identification key relies heavily on the morphology of the cerci, including their ridges, carinas, and overall ML shape. Other features, such as body coloration, may also be used as secondary characteristics. Frequently the examined structures may be hidden, depending on the specimen, so we recommend relaxing and spreading the anal appendages to obtain a better view of the diagnostic characters.

1. Paraprocts poorly developed (vestigial); overall aspect of cercus oblong, swollen ( Figs. 2a–c , 4a–c ); in most species, BP forming a hollow space that varies in size and shape ( Figs. 2a–b , 15c , 18c ); ML with a developed ridge or carina ( Figs. 3a–c ), frequently dividing ML into two plates and forming an additional upper plate ( Figs. 2c–d , 18c–d , 25c–e )................................................................................................. Group A key (couplet 2)

1’. Paraprocts developed, being short (ca. 1/3 of cercus length, Fig. 4d ), medium (ca. 2/3 of cercus length, Fig. 4e ) or long sized (over 1/2 of cercus length, Fig. 4f ); BP compact, not forming a hollow space ( Figs. 2e–h , 7e–f ); ML entire, not divided by a ridge or carina ( Figs. 3d–f , 8c–e ), only with small teeth in a few species ( Figs. 55c–e ); a longitudinal toothed ridge above ML ( Figs. 2g –h , 3e–f , 8c–e )............................................................. Group B key (couplet 2)

Key to Group A species

2 (1). In the medial portion of cercus (MP, see Fig. 1a ), medial lobe (ML) consisting of a single plate with a medial carina, reaching or not ML apex (e.g., Figs. 3a–c , 12f–j , 38c ).................................................... 3

2’. In the MP, ML consisting of two plates (upper and lower), sustained by a medial ridge (e.g., Figs. 2c–d , 18c–d , 21e ).... .............................................................................................. 19

3 (2). BP consisted of a hairy tubercle or apophysis, not forming a hollow ventral concavity (e.g., Figs. 4b–c , 65c–d )....... 4

3’. BP lacking a tubercle, its ventral portion poorly dilated or forming a hollow, dilated ventral concavity, varying in expansion ventrally and posteriorly (e.g., Figs. 2a–b , 15c , 18c )...................................................... 6

4 (3). ML narrow, with squared apex ( Fig. 65c ), ridge slightly curved, small, bearing strong teeth ( Fig. 65c–d )................................................................................................. H. triangulare

4’. ML broad, with roughly squared apex, ridge bearing small teeth (e.g., Figs. 54c–d )............................. 5

5 (4’). Head lacking a basal line of the frontoclypeal suture; restricted to Northern Brazil ( Figs. 38c–d ).......... H. ictericum

5’. Head with a basal line on the frontoclypeal suture; restricted to the Venezuelan Tepuis ( Figs. 54c–d )........ H. pemon

6 (3’). BP the longest cercus portion, little dilated ventrally; MP and AP subequal in length (e.g., Figs. 60d–f )............. 7

6’. BP not the longest cercus portion, moderately to dilated ventral concavity; MP and AP not subequal in length (e.g., Fig. 12g , 28c , 30c ).................................................................................... 9

7 (6). BP margin straight ( Figs. 26c–d , 60d ); ML broad, roughly squared; ML apex not bilobate, or if so, bearing only a small cleft ( Figs. 26c , 60d–g )............................................................................. 8

7’. BP slightly curved inwards ( Fig. 24c ); ML narrow, ridge bearing strong teeth ( Fig. 24e ); ML apex bilobate, W shaped ( Figs. 24c–e )....................................................................... H. cinnamomeum

8 (7). ML ridge short, nearly straight, reaching or not ML apex ( Fig. 60f ); ML apex blunt, lacking cleft......... H. silvarum

8’. ML ridge long, bearing an elevated ridge ( Fig. 26c ); ML apex with a small cleft ( Fig. 26d )................. H. cooki

9 (6’). Overall body coloration consisting of shades of blue and green, with black background (e.g., Figs. 28a–b , 30b , 36b ).... .............................................................................................. 10

9’. Overall body coloration consisting of shades of yellow and orange, with black background (e.g., Figs. 12a–e , 27a , 46ab )............................................................................................ 12

10 (9). ML ridge not reaching its apex ( Fig. 28c ); ML apex rounded, not bilobate ( Figs. 28c–d )................... H. cyane

10’. ML ridge almost reaching its apex ( Figs. 30c , 36 ); ML apex not rounded, bilobate ( Figs. 30d , 36 c–d )............. 11

11 (10’). Lobes of ML apex rounded ( Fig. 30c )......................................................... H. denisye

11’. Anterior lobe of ML acute, posterior lobe rounded ( Figs. 36c–d )...................................... H. gorbi

12 (9’). ML apex cleft or bilobate (e.g., Figs. 12f–j , 27d , 46d ).................................................... 13

12’. ML apex entire or undulated, not cleft or bilobate (e.g., Figs. 15c , 37c–d , 45c–d ).............................. 15

13 (12). ML ridge nearly straight, long, reaching its apex, lacking an additional ridge and hollow space, bearing several small teeth ( Figs. 12f , 27e–f )................................................................................ 14

13’. ML ridge short, bearing strong teeth ( Fig. 46c ), with an additional ridge forming a hollow space posteriorly ( Figs. 46e–f )..................................................................................... H. luizfelipei

14 (13). ML longer than wide, its apex bilobate, ‘W’ shaped ( Figs. 27d ).............................. H. corderoi sp. nov.

14’. ML wider than long, apex not bilobate varying in width, but ending in a usually narrow cleft apex ( Figs. 12f–j )........................................................................................... H. aurantiacum

15 (12’). BP not greatly expanded or dilated ventrally (e.g., Fig. 15c )............................................... 16

15’. BP expanded ventrally, forming a hollow concavity (e.g., Figs. 48d , 49c ).................................... 17

16 (15). BP densely hairy ( Fig. 15c ); ML ridge bearing strong teeth, reaching its apex ( Fig. 15c ); in lateral view, BP with a dorsobasal expansion ( Fig. 15d ); ML apex square ( Fig. 15c )....................................... H. beschkii

16’. BP not densely hairy; ML formed by a broad plate ( Figs. 45c–d ); ML ridge short, not reaching its apex ( Fig. 45d ); in lateral view, BP lacking dorsobasal expansion; ML apex rounded ( Fig. 45d )............................... H. lencionii

17 (15’). ML with two parallel ridges on its medial space ( Fig. 37d ), plus an additional basal ridge ( Fig. 37c ); ML apex undulate ( Figs. 37c–d ).............................................................................. H. gracile

17’. ML with a single ridge on medial space ( Figs. 48c–d , 49c ), lacking an additional basal ridge; ML apex not undulate ( Figs. 48c , 49c )....................................................................................... 18

18 (17’). ML ridge long, sinuous, bearing strong teeth, reaching ML apex ( Fig. 49c ); AP margin lacking any basal swelling ( Fig. 49c )................................................................................ H. mantiqueirae

18’. ML ridge short, bearing small teeth, not reaching ML apex ( Fig. 48c ); AP margin bearing a small basal swelling ( Fig. 48d )................................................................................. H. makiritare

19 (2’). BP uniquely with a long, narrow ventral branch ( Figs. 51c–d )..................................... H. muryense

19’. BP lacking a long, narrow ventral branch, instead forming a hollow, dilated ventral concavity, varying in expansion (e.g., Figs. 2a–b , 18c )................................................................................. 20

20 (19’). Upper plate of MP subequal in size to lower plate (e.g., Figs. 21e , 25c–e , 56c–d ).............................. 21

20’. Upper plate of MP smaller than lower plate (e.g., Fig. 18c–d , 43c–e , 52e ).................................... 23

21 (20). Upper plate rounded, lower plate roughly squared ( Figs. 21e , 56c )......................................... 22

21’. Upper plate and lower plate with similar shape ( Figs. 25c–e )....................................... H. consors

22 (21). Upper plate broader than lower plate; lower plate bearing two carinae and squared apex ( Fig. 21e )........... H. cauei

22’. Upper plate broader than lower plate; lower plate lacking two carinae, bearing acute apex ( Fig. 56c )....... H. petiense

23 (20’). BP hollow, greatly expanded ventrally, uniquely surpassing MP level ( Figs. 52e–h )..................... H. ovatum

23’. BP hollow, but ventral expansion not surpassing MP level (remainder of Group A species)...................... 24

24 (23’). Upper plate narrow, longer than wide (e.g., Figs. 18c–d , 43c–e )............................................ 25

24’. Upper plate in a different shape (small, with rounded edges, as in Figs. 44c , 35c–d ; short, wider than long, as in Fig. 64d ; or inverted triangle, with angled corners, as in Fig. 57e ).................................................. 26

25 (24). BP forming a greatly ventral expanded concavity ( Fig. 43c ); ML ridge not centered ( Figs. 43d–e )........ H. itacolomii

25’. BP ventral concavity not greatly expanded ( Figs. 18c–d ); ML ridge centered ( Fig. 18d )................ H. brianmayi

26 (24’). Upper plate with rounded edges (e.g., Figs. 44c , 35c–d ).................................................. 27

26’. Upper plate with angled edges (e.g., Figs. 64d , 57e )..................................................... 28

27 (26). ML apex rounded ( Figs. 34c–e ).......................................................... H. flavovittatum

27’. ML apex roughly square ( Figs. 35c , 44c ).............................................................. 29

28 (26’). Upper plate bearing a posterior row of small teeth, not centered ( Fig. 44c ); broadly developed BP ventral concavity; ridge fused with ML at the apex ( Fig. 44d )...................................................... H. johndeaconi

28’. Upper plate bearing a posterior row of strong teeth, centered ( Fig. 35c ); moderately developed BP concavity; ridge fused with ML up to 1/2 of lower plate ( Fig. 35d ).............................................. H. freddiemercuryi

29 (27’). Upper plate wider than long, roughly triangular, bearing small teeth on its border ( Figs. 64d–f ); ML apex acute ( Fig. 64f ) H. tiradentense

29’. Upper plate longer than wide, shaped like an inverted triangle (e.g., Figs. 57e , 58c , 63c ); ML apex squared (e.g., Fig. 63c ) or bilobate (e.g., Fig. 57e )......................................................................... 30

30 (29’). ML apex not bilobate, roughly squared ( Figs. 58c , 63c–d )................................................ 31

30’. ML apex bilobate, ‘W’ shaped ( Fig. 57e ).................................................... H. rogertaylori

31 (30). Posterior margin of upper plate short, straight, bearing small teeth, anterior margin subequal in size ( Fig. 63c ); upper plate markedly concave at its middle ( Fig. 63d ); ML apex acutely squared ( Figs. 63c–d )........................ H. thais

31’. Posterior margin of upper plate long, bearing a row of strong teeth, anterior margin short ( Fig. 58c ); upper plate slightly concave at its middle; ML apex roughly squared ( Fig. 58c )......................................... H. roquei

Key to Group B species

2 (1’). Paraprocts very long, surpassing 1/2 of cercus, almost reaching its apex (e.g., Figs. 4f . 11c–d ).................... 4

2’. Paraprocts from short to medium size, not surpassing 1/2 of cercus.......................................... 3

3. Paraprocts medium sized, almost reaching 1/2 of cercus length (e.g., Figs. 4e , 17d , 39e )......................... 5

3’. Paraprocts short, thin, not surpassing 1/3 of cercus length (e.g., Figs. 4d , 31b , 59c , 62d–e , 67d )................... 7

4 (2). In lateral view, cercus arched at midlength ( Fig. 53c ); abdomen 52 mm ............................ H. palmichale

4’. In lateral view, overall cercus shape less arched ( Fig. 11c ) than H. palmichale ( Fig. 53c ); abdomen 49 mm ... H. archon

5 (3’). Ridge above ML long, sinuous consisting of small teeth, and a marked carina ( Figs. 39d–f ); in lateral view, ML bent downwards ( Fig. 39f ); AP the shortest ( Fig. 39d ); S9–10 almost entirely black or dark brown............. H. icterops

5’. Morphology as in H. icterops , but larger yellow areas on head, thorax and abdomen............................ 6

6 (5’). Small yellow spots above each antenna ( Fig. 17a ); S9–10 dark brown/yellow.......................... H. breweri

6’. Small spots above antennae absent ( Fig. 61a ); S9–10 paler...................................... H. simulatum

7 (3’). Overall body coloration consisting of shades of blue and gray, with black background ( Figs. 13a–b ), S8–10 yellow ( Figs. 13c–e ).................................................................................. H. azulum

7’. Overall body coloration consisting of shades of yellow and orange, with black background, or largely red areas such as head and abdomen................................................................................ 8

8. Largely red abdomen (e.g., H. erythrogastrum and H. albifrons ) or head (e.g., H. rubrifulvum ).................... 9

8’. Abdomen and head not red......................................................................... 11

9 (8). Abdomen largely red, head largely black................................................. H. erythrogastrum

9’. Some other combination of body coloration........................................................... 10

10 (9’). Head and mouthparts largely pale; S3–S7 black and red, S8–10 largely red........................... H. albifrons

10’. Head red, remainder of body pale yellow.................................................. H. rubrifulvum

11 (8’). Longitudinal toothed ridge not partially covering ML in dorsal and dorsolateral views (e.g., Figs. 9 c–e , 55c–e ; 62c ).... .............................................................................................. 12

11’. Longitudinal toothed ridge partially covering ML in dorsal and dorsolateral views (e.g., Figs. 2g –h , 7e–f , 10f , 14f–g )... .............................................................................................. 19

12 (11). ML bearing small teeth on its plate (e.g., Figs. 55c–e ; 62c )............................................... 13

12’. ML bearing no teeth or carina on its plate (e.g., Figs. 8c–e , 10g , 14d–e )..................................... 14

13 (12). BP the longest portion, with nearly straight margin ( Fig. 55e ); MP subequal in length to AP ( Fig. 55e ); ridge above ML long, bearing small teeth in a straight line, not reaching its apex ( Figs. 55c–e ); ML apex acute ( Figs. 55c–e ).............................................................................................. H. peregrinum

13’. BP subequal in length to AP, slightly convex margin ( Fig. 62c ); MP the shortest ( Fig. 62c ); ridge above ML bearing strong teeth on a nearly straight line, reaching its apex; ML apex with a small cleft ( Figs. 62c–e )................. H. tatama

14 (12’). BP the longest cercus section in length (e.g., Figs. 9c–e , 20e , 67e ).......................................... 15

14’. BP not the longest cercus section in length (e.g., Fig. 7e , 23c ; 31c )......................................... 18

15 (14). Ridge above ML bearing strong teeth in a single row ( Figs. 20d–e ); AP small, subequal to MP ( Fig. 20e )................................................................................................. H. calendulum

15’. Ridge above ML consisting of small denticles; AP not as above............................................ 16

16 (15’). Ridge above ML consisted of very small denticles in a single row ( Figs. 9e , 16e ).............................. 17

16’. Ridge above ML consisting of a patch of small denticles, not in a single row ( Figs. 67d–e )............... H. valgum

17 (16). MP lacking an elevated crest on its medial margin ( Figs. 9c–e )..................................... H. alienum

17’. MP bearing an elevated crest on its medial margin ( Figs. 16d–e )................................... H. bickorum

18 (14’). Ridge above ML bearing strong teeth on a single row ( Figs. 31b–c ); ML apex acute ( Figs. 31b–c )........ H. eboratum

18’. Ridge above ML bearing very small denticles ( Figs. 23c–d ); ML apex blunt ( Figs. 23c–d )............... H. chrysops

19 (11’). BP with a nearly straight margin, bearing no swelling or convexity (e.g., Figs. 7e–f , 19c , 47c–e ).................. 20

19’ BP with some degree of convexity, varying from small to largely swollen (e.g., Figs. 14d–g , 22c–e , 33c–d )......... 23

20 (19). MP the shortest portion of cercus in length (e.g., Figs. 7e , 19c , 47c–e )...................................... 21

20’. Portions of cercus subequal in size or AP the longest (e.g., Figs. 8c–e , 66c–e )................................. 22

21 (20). Ridge above ML upcurved, bearing strong teeth not spaced ( Fig. 19c ); MP–AP junction forming a nearly straight line with AP ( Fig. 19c ); ML apex rounded ( Fig. 19c )................................................. H. calafatiensis

21’. Ridge above ML formed by spaced and very strong teeth ( Figs. 47c–e ); MP–AP junction forming an angled corner; ML apex acute ( Figs. 47c–e )...................................................................... H. majus

22 (20’). Portions of cercus all subequal in size ( Fig. 8d ); ridge above ML long, straight, its apex forming a narrow tip ( Figs. 8c–e ); ML apex rounded ( Fig. 8e ); mouthparts and frons largely pale, not yellow ( Fig. 8a ).................... H. albifrons

22’. AP the longest cercus portion, slightly longer than BP ( Fig. 66e ); ridge above ML short, consisting of strong teeth ( Figs. 66c–e ); ML apex acute ( Figs. 66c–e ); mouthparts and frons yellow............................... H. tricellulare

23 (19’). BP margin greatly swollen or expanded (e.g., Figs. 14d–e , 22c–d , 33c–d ).................................... 24

23’. BP margin only slightly convex (e.g., Figs. 10d–g , 16d–e )................................................ 25

24 (23). Ridge above ML roughly bean-shaped ( Figs. 22c–e )....................................... H. chlorotaeniatum

24’. Ridge above ML nearly straight (e.g., Figs. 42e–i , 29c ).................................................. 26

25 (23’). Ridge above ML nearly straight, with two parallel rows of teeth ( Fig. 33c ); MP-AP junction not marked, nearly straight ( Fig. 33f )............................................................................. H. flavidorsum

25’. Ridge above ML with a single row of teeth; MP-AP junction marked, being rounded or angled ( Figs. 14d–g , 50c–e ).... .............................................................................................. 27

26 (24’). Ridge above ML bearing small teeth (e.g., Figs. 42e–i , 29c )............................................... 28

26’. Ridge above ML bearing strong teeth ( Figs. 7g –h ; Fig. 10g ).............................................. 29

27 (25’). BP the longest cercus section ( Fig. 14d )......................................................... H. bariai

27’. All portions of cercus subequal in length ( Fig. 50c )............................................. H. mitratum

28 (26). Ridge above ML with a single row of teeth ( Figs. 29c–d ); male postclypeus yellow with brown transverse line ( Fig. 29a ); in lateral view, cercus slightly elbowed along midlength ( Fig. 29e ); restricted to the Colombian Amazon................................................................................................. H. demarmelsi

28’. Ridge above ML forming a roughly rounded teeth arrangement between the two rows ( Figs. 42e–f ); male postclypeus yellow with a black transversal line ( Figs. 42a, 42c ), or lacking a transversal line ( Fig. 42b ); in lateral view, cercus not elbowed along midlength; Colombian Amazon, Ecuador, Peru, Brazil, and Bolivia........................ H. inca

29 (26’). Ridge above ML sinuous, bearing strong teeth, with a carina parallel to the ridge ( Figs. 7e–f ); ML apex blunt ( Figs. 7g –h ).............................................................................. H. aequatoriale

29’. Ridge above ML nearly straight, with an additional row of teeth below the main ridge ( Figs. 10d–g ); ML apex acute ( Figs. 10d–e, g )........................................................................... H. angustipenne

Species Accounts

Lencioni (2013), Bota-Sierra et al. (2017), and Stand-Pérez et al. (2019) extensively commented on the taxonomy and ecology of most of the species listed. Thus, in the following accounts we provide complementary information. We made no additional conservation comments on species assessed as Least Concern in the IUCN Red List.

Figures

FIGURE 1. The Heteragrion cercus, showing the three main regions of the appendage: basal portion (BP), medial portion (MP) and apical portion (AP). Note that the proportions between cercus (a) and (b) are quite different and serve as a useful tool for species identification. ML: medial lobe. Figure b provided by Rosser Garrison and Natalia von Ellenrieder.

FIGURE 2. The Heteragrion cercus, showing some differences between the two groups of species: (a–d) Group A species, (e–h) Group B species. BP: cercus basal portion; ML: medial lobe. Figures a, g–h provided by Rosser Garrison and Natalia von Ellenrieder.

FIGURE 3. The Heteragrion cercus, showing some differences between the two groups of species: (a–c) Group A species, (d–f) Group B species. ML: medial lobe.

FIGURE 4. The Heteragrion cercus, showing some differences between the two groups of species: (a–c) Group A species, (d–f) Group B species. BP: basal portion. Figure d provided by Rosser Garrison and Natalia von Ellenrieder.

FIGURE 5. Some individual variation in coloration and morphology in Heteragrion species: H. ictericum, left column; H. silvarum, right column. Images provided by Rosser Garrison and Natalia von Ellenrieder.

FIGURE 6. Map showing the distribution of Heteragrion species from Group A (green dots) and Group B (red dots). We used no more than five dots per species, in order not to cover the dots where the two groups overlapped in distribution.

FIGURE 7. Heteragrion aequatoriale: (a–d) anterior view of head, showing minimal variation in color pattern; (e) cercus in dorsal view, showing the proportions of basal portion (BP), medial portion (MP), and apical portion (AP); (f) cercus in mediodorsal view; (g–h) close up of MP, showing ridge above medial lobe (ML) and small cleft at junction of ridge-ML. Figures e–h provided by Rosser Garrison and Natalia von Ellenrieder.

FIGURE 8. Heteragrion albifrons: (a) anterior view of head; (b) lateral view of pterothorax; (c–e) cercus in mediodorsal view. BP: basal portion; MP: medial portion; AP: apical portion.

FIGURE 9. Heteragrion alienum: (a) anterior view of head; (b) lateral view of pterothorax; (c) dorsal view of cercus, showing longitudinal depression on AP; (d–e) cercus in mediodorsal view. AP: apical portion.

FIGURE 10. Heteragrion angustipenne: (a, c) anterior view of male head; (b) female head; (d, f) dorsal view of cercus; (e, g) mediodorsal view of cercus; (c) adapted from Williamson (1919), based on a male examined by Calvert (1909). ML: medial lobe. Figures f–g provided by Rosser Garrison and Natalia von Ellenrieder.

FIGURE 11. Heteragrion archon: (a) anterior view of head; (b) lateral view of pterothorax; (c) lateral view of anal appendages; (d) mediodorsal view of anal appendages; (a–b) adapted from the original drawings by De Marmels (2008). Figures c–d provided by Rosser Garrison and Natalia von Ellenrieder.

FIGURE 12. Heteragrion aurantiacum: (a–c) anterior view of head; (d–e) lateral view of pterothorax; (f–g, i) mediodorsal view of cercus; (h, j) close up on the apical portion of medial lobe (ML) showing some morphological variation.

FIGURE 13. Heteragrion azulum: (a) anterior view of head; (b) lateral view of pterothorax; (c) dorsal view of cercus; (d) close up, MP-AP; (e) mediodorsal view of cercus; (f) close up, ridge and ML. MP: medial portion; AP: apical portions; ML: medial lobe. Figures a–f provided by Rosser Garrison and Natalia von Ellenrieder.

FIGURE 14. Heteragrion bariai: (a–b) anterior view of head; (c) lateral view of pterothorax; (d, g) mediodorsal view of cercus; (e) medial view of cercus; (f) dorsal view of cercus. BP: basal portion; MP: medial portion; AP: apical portion; ML: medial lobe. Figures f–g provided by Rosser Garrison and Natalia von Ellenrieder.

FIGURE 15. Heteragrion beschkii: (a) anterior view of head; (b) lateral view of pterothorax; (c) mediodorsal view of cercus; (d) lateral view of cercus. BP: basal portion.

FIGURE 16. Heteragrion bickorum: (a–b) anterior view of head; (c) lateral view of pterothorax; (d) mediodorsal view of cercus; (e) close up of MP-AP in medial view, showing the elevated crest and the ridge above ML; (f) medial view of cercus; (g) dorsal view of cercus.

FIGURE 17. Heteragrion breweri: (a) anterior view of head; (b) lateral view of pterothorax; (c) mediodorsal view of cercus; (d) lateral view of anal appendages. ML: medial lobe.

FIGURE 18. Heteragrion brianmayi: (a) anterior view of head; (b) lateral view of pterothorax; (c–d) mediodorsal view of cercus.

FIGURE 19. Heteragrion calafatiensis: (a) anterior view of head; (b) lateral view of pterothorax; (c) mediodorsal view of cercus; (d) lateral view of cercus. AP: apical portion of cercus; MP: medial portion; ML: medial lobe.

FIGURE 20. Heteragrion calendulum: (a–c) anterior view of head; (d–e) mediodorsal view of cercus. MP: medial portion; (c) adapted from Stand-Pérez et al. (2019). AP: apical portion.

FIGURE 21. Heteragrion cauei: (a) anterior view of head; (b) lateral view of pterothorax; (c) dorsal view of cercus; (d–e) mediodorsal view of cercus.

FIGURE 22. Heteragrion chlorotaeniatum: (a) anterior view of head; (b) lateral view of pterothorax; (c–d) mediodorsal view of cercus; (e) dorsal view of cercus. BP: basal portion; ML medial lobe.

FIGURE 23. Heteragrion chrysops: (a) anterior view of head; (b) lateral view of pterothorax; (c–d) mediodorsal view of cercus; (e) closeup of cercus BP in medial view. BP: basal portion; ML: medial lobe.

FIGURE 24. Heteragrion cinnamomeum: (a) anterior view of head; (b) lateral view of pterothorax; (c–e) mediodorsal view of cercus. BP: basal portion; ML: medial lobe. Figure e provided by Rosser Garrison and Natalia von Ellenrieder.

FIGURE 25. Heteragrion consors: (a) anterior view of head; (b) lateral view of pterothorax; (c–e) mediodorsal view of cercus.

FIGURE 26. Heteragrion cooki: (a) anterior view of head; (b) lateral view of pterothorax; (c–d) mediodorsal view of cercus. ML: medial lobe.

FIGURE 27. Heteragrion corderoi sp. nov. male holotype: (a) dorsal view of head; (b) lateral view of habitus; (c) lateral view of pterothorax; (d) dorsal view of pterothorax (e–f) mediodorsal view of cercus. BP: basal portion; ML: medial lobe.

FIGURE 28. Heteragrion cyane: (a) anterior view of head; (b) lateral view of pterothorax; (c) mediodorsal view of cercus; (d) dorsal view of cercus. ML: medial lobe.

FIGURE 29. Heteragrion demarmelsi: (a) anterior view of male head; (b) anterior view of female head; (c) mediodorsal view of cercus; (d) dorsal view of cercus; (e) lateral view of cercus; BP: basal portion; MP: medial portion; ML: medial lobe.

FIGURE 30. Heteragrion denisye: (a) anterior view of head; (b) lateral view of pterothorax; (c) mediodorsal view of cercus; (d) laterodorsal view of cerci. ML: medial lobe.

FIGURE 31. Heteragrion eboratum: (a) anterior view of head; (b) dorsal view of anal appendages; (c) mediodorsal view of cercus; (a) adapted from the original drawings by Donnelly (1965). AP: apical portion; ML: medial lobe.

FIGURE 32. Heteragrion erythrogastrum: (a) anterior view of head; (b) lateral view of pterothorax; (c) dorsal view of cercus; (d) mediodorsal view of cercus. ML: medial lobe.

FIGURE 33. Heteragrion flavidorsum: (a) anterior view of head; (b) lateral view of pterothorax; (c–d) medial view of cercus; (e–f) dorsal view of cercus; (g) mediodorsal view of cercus. BP: basal portion; MP: medial portion. Figures f–g provided by Rosser Garrison and Natalia von Ellenrieder.

FIGURE 34. Heteragrion flavovittatum: (a) anterior view of head; (b) lateral view of pterothorax; (c–e) mediodorsal view of cercus. Figure e provided by Rosser Garrison and Natalia von Ellenrieder.

FIGURE 35. Heteragrion freddiemercuryi: (a) anterior view of head; (b) lateral view of pterothorax; (c) mediodorsal view of cercus; (d) close up of MP, showing the ML plates. MP: medial portion; ML: medial lobe.

FIGURE 36. Heteragrion gorbi: (a) anterior view of head; (b) lateral view of pterothorax; (c–e) mediodorsal view of cercus.

FIGURE 37. Heteragrion gracile: (a) anterior view of head; (b) lateral view of pterothorax; (c) mediodorsal view of cercus; (d) close up of MP, showing the two-ridged ML. MP: medial portion; ML: medial lobe.

FIGURE 38. Heteragrion ictericum: (a) anterior view of head; (b) lateral view of pterothorax; (c) mediodorsal view of cercus; (d) lateral view of cercus. BP: basal portion; ML: medial lobe.

FIGURE 39. Heteragrion icterops: (a) anterior view of head; (b–c) lateral view of pterothorax; (d, f) mediodorsal view of cercus; (e) dorsal view of anal appendages. ML: medial lobe. Figures e–f provided by Rosser Garrison and Natalia von Ellenrieder.

FIGURE 42. Heteragrion inca: (a–c) anterior view of head; (d) lateral view of pterothorax; (e–f, h) mediodorsal view of cercus; (g, i) close up showing the two MP ridges above ML; (c) adapted from the drawing by Williamson (1919). MP: medial portion of cercus; ML: medial lobe. Figures h–i provided by Rosser Garrison and Natalia von Ellenrieder.

FIGURE 43. Heteragrion itacolomii: (a) anterior view of head; (b) lateral view of pterothorax; (c–d) mediodorsal view of cercus; (e) close up of MP, showing the ML plates. MP: medial portion; ML: medial lobe.

FIGURE 44. Heteragrion johndeaconi: (a) anterior view of head; (b) lateral view of pterothorax; (c) mediodorsal view of cercus; (d) lateral view of cercus.

FIGURE 45. Heteragrion lencionii: (a) anterior view of head; (b) lateral view of pterothorax; (c–d) mediodorsal view of cercus. ML: medial lobe.

FIGURE 46. Heteragrion luizfelipei: (a) anterior view of head; (b) lateral view of pterothorax; (c–d) mediodorsal view of cercus; (e–f) close up of MP, showing the hollow space formed by a carina on ML. MP: medial portion; ML: medial lobe.

FIGURE 47. Heteragrion majus: (a) anterior view of head; (b) lateral view of pterothorax; (c, e) mediodorsal view of cercus; (d) dorsal view of cercus. ML: medial lobe; AP: apical portion. Figure e provided by Rosser Garrison and Natalia von Ellenrieder.

FIGURE 48. Heteragrion makiritare: (a) anterior view of head; (b) lateral view of pterothorax; (c) dorsal view of cercus; (d) mediodorsal view of cercus; (a–b) adapted from De Marmels (2004). ML: medial lobe. Figures c–d provided by Rosser Garrison and Natalia von Ellenrieder.

FIGURE 49. Heteragrion mantiqueirae: (a) anterior view of head; (b) lateral view of pterothorax; (c) mediodorsal view of cercus; (d) lateral view of cercus; (a) adapted from Machado (2006). MP: medial portion; ML: medial lobe.

FIGURE 50. Heteragrion mitratum: (a) anterior view of head; (b) lateral view of pterothorax; (c–d) mediodorsal view of cercus; (e) dorsal view of cercus. BP: basal portion; MP: medial portion; ML: medial lobe; AP: apical portion.

FIGURE 51. Heteragrion muryense: (a) anterior view of head; (b) lateral view of pterothorax; (c–d) mediodorsal view of cercus. BP: basal portion; ML: medial lobe.

FIGURE 52. Heteragrion ovatum: (a) lateral view of pterothorax; (b) anterior view of head, lateral view of thorax, and S1–2; (c–d) dorsal view of pterothorax; (e–f) mediodorsal view of cercus; (g–h) lateral view of cercus. BP: basal portion; MP: medial portion. Figures a–j provided by Rosser Garrison and Natalia von Ellenrieder.

FIGURE 53. Heteragrion palmichale: (a) anterior view of head; (b) lateral view of pterothorax; (c) lateral view of anal appendages; (a–b) adapted from Hartung (2002).

FIGURE 54. Heteragrion pemon: (a) anterior view of head; (b) lateral view of pterothorax; (c–d) mediodorsal view of cercus.

FIGURE 55. Heteragrion peregrinum: (a–b) anterior view of head; (c–d) dorsal view of cerci; (e) mediodorsal view of cercus. BP: basal portion; ML: medial lobe.

FIGURE 56. Heteragrion petiense: (a) anterior view of head; (b) lateral view of pterothorax; (c) mediodorsal view of cercus; (d) closeup of MP, showing ML plates. MP: medial portion; ML: medial lobe.

FIGURE 57. Heteragrion rogertaylori: (a–b) anterior view of head; (c–d) lateral view of pterothorax; (e–g) mediodorsal view of cercus. ML: medial lobe.

FIGURE 58. Heteragrion roquei: (a) anterior view of head; (b) lateral view of pterothorax; (c) mediodorsal view of cercus; (d) lateral view of cercus. ML: medial lobe.

FIGURE 59. Heteragrion rubrifulvum: (a) anterior view of head; (b) lateral view of pterothorax; (c) dorsal view of anal appendages; (d) mediodorsal view of anal appendages; (a–b) adapted from Donnelly (1992). AP: apical portion; ML: medial lobe.

FIGURE 60. Heteragrion silvarum: (a–b) anterior view of head; (c) lateral view of pterothorax; (d–g) mediodorsal view of cercus. BP: basal portion; MP: medial portion; AP: apical portion.

FIGURE 61. Heteragrion simulatum: (a–b) anterior view of head; (c) lateral view of pterothorax; (d) mediodorsal view of cercus; (e) lateral view of cercus; (a) adapted from Williamson (1919), (b–c) adapted from De Marmels (1989). ML: medial lobe.

FIGURE 62. Heteragrion tatama: (a) anterior view of head; (b) lateral view of pterothorax; (c–d) mediodorsal view of anal appendages; (e) dorsal view of anal appendages. MP: medial portion; ML: medial lobe.

FIGURE 63. Heteragrion thais: (a) anterior view of head; (b) lateral view of pterothorax; (c–d) mediodorsal view of cercus; (a) adapted from Machado (2015). ML: medial lobe.

FIGURE 64. Heteragrion tiradentense: (a–b) anterior view of head; (c) lateral view of pterothorax; (d–f) mediodorsal view of cercus.

FIGURE 65. Heteragrion triangulare: (a) anterior view of head; (b) lateral view of pterothorax; (c–d) mediodorsal view of cercus.

FIGURE 66. Heteragrion tricellulare: (a) anterior view of head; (b) lateral view of pterothorax; (c) mediodorsal view of cercus; (d–e) dorsal view of cercus. ML: medial lobe; AP: apical portion.

FIGURE 67. Heteragrion valgum: (a–b) anterior view of head; (c) lateral view of pterothorax; (d) dorsal view of cercus; (e) mediodorsal view of cercus; (b–c) adapted from Donnelly (1992). BP: basal portion.