Enallagma tobagoensis Donnelly & Michalski 2025, sp. nov.
Creators: name: Donnelly, Thomas W.
name: Michalski, John
Publisher: name: Zenodo
Year: 2025
Subjects: Biodiversity
Taxonomy
Animalia
Arthropoda
Insecta
Odonata
Coenagrionidae
Enallagma
Enallagma tobagoensis

description: Enallagma tobagoensis Donnelly & Michalski, sp. nov.
Figs. 1 (habitus ♂ holotype), 2 (S1– 3 paratype), 3 (wings paratype), 4 appendages (holotype), 11 right cercus (paratype), 12 (genital ligula, paratype), 13 (map).
Etymology. Named tobagoensis (Latinized name) for Tobago.
Specimens examined. 2 ♂♂. Holotype ♂ (lacking genital ligula): TOBAGO, St. John Parish, stream along Northside Road (N 11.2868°, W 60.6808°, 8 August 2019, Thomas W. Donnelly & John Michalski leg. (FSCA); Paratype ♂ (lacking head and a pair of wings), same data as holotype (RWG).
A small, largely black Enallagma with appendages almost identical to those of E. cyathigerum and E. annexum.
Enallagma tobagoensis ♂
Tobago: St. John Parish, stream along Northside Road
Description of male holotype
Head (Fig. 1, partially crushed dorsoventrally): Labrum, anteclypeus, antefrons, genae, and base of antennae blue, postfrons shining black, epicranium dull black except for a pair of blue triangular postocular spots; antennae missing; rear of head black medially, pale laterally.
Thorax. Prothorax largely black, anterior lobe blue, middle lobe black, posterior lobe black except for narrow blue rim, propleuron pale blue. Pterothorax (Fig. 1) blue anteriorly becoming blue-green laterally with black middorsal and humeral stripes; blue antehumeral stripe linear, slightly narrowing dorsally; mesal portion of mesostigmal plates and median half of mesepisterna black; antealar crests black; black humeral stripe straight, abruptly widened at ventral fifth, and about one third width of middorsal stripe. Remainder of thorax blue green except following black areas: anterior half of mesinfraepisternum, narrow metapleural stripe. Legs pale with extensor surfaces of femora black; basal black lines on exterior surfaces and basal fourth to half of flexor surfaces of tibiae; tarsi and armature black.
Wings (as in Fig. 3) hyaline; pterostigma trapezoidal, dark brown, surmounting slightly less than 1 cell in all wings; postnodals Fw 10/11, Hw 10 (tip pf Hw slightly deformed)/9; postquadrangular cells Fw 3/3, Hw 3/3; RP 2 at Fw 5.6/5.5, Hw 5/4.6.
Abdomen (Fig. 1) with pale colors blue, remainder mostly black as follows; S1 dorsally quadrangular black at basal 0.60 and a lateral round spot at basal fifth; S2 dorsally with a diamond-shaped black spot occupying apical 0.80 of segment, anteriorly disjunct from S1, posteriorly joining black annulus, angulate expansion of dorsal spot at apical fourth; laterally with a narrow black lateral stripe ending at apical fourth (as in Fig. 2); S3 dorsally with a parallel black stripe terminating at basal fifth, this stripe with lateral quadrate expansion at apical fifth; S3–7 as in S3 but black more extensive; S8–9 blue laterally with a narrow irregular incomplete black stripe; S10 black, narrowly pale ventrally.
Cercus slightly shorter than paraproct, strongly upturned at apex (Fig. 4c), in dorsal (Fig. 4b) and mediodorsal (Figs. 4a, 11) views with a small pale tubercle running diagonally across its apex, its medial margin adjacent to medially directed polished triangular black tooth, with an underlying small semicircular lobe medial to black tooth.
Genital ligula (as in Fig. 12) broadly quadrate in ectal view, with apicolateral triangular lobe followed by a lateroventral angulate projection.
Dimensions. Hw 14.0, abdomen 21.0, total length 26.0.
Variation in paratype. Paratype male similar to holotype but with different venation counts as follows (Fig. 3); postnodals Fw 9/8, Hw 7/7; postquadrangular cells Fw 3/3, Hw 3/3; RP 2 at Fw 4/5, Hw 4/4.
Dimensions of paratype. (head missing): Hw 20.0, abdomen 20.0, total length?
Diagnosis. The appendage and genital ligula morphology (Figs. 4, 11, 12) are like those of E. annexum (Fig. 5), E. circulatum (Fig. 6), E. cyathigerum cyathigerum (Fig. 7), E. cyathigerum risi (Fig. 8), E. deserti (Fig. 9) and E. vernale (Fig. 10) all of which have been illustrated in several papers (see below). The taxonomic status of the E. cyathigerum complex is not fully understood and has been discussed by several authors (Ris 1928; Lieftinck 1966; Dumont 1975; Jurzitza 1975; Garrison 1984; Donnelly 1963, 1989; May 1997; Jacquemin & Boudot 1999; Kosterin & Zaika 2010; Samraoui et al. 2002; Stoks et al. 2005). It is beyond the scope of this paper to review the status of the several names associated with this Holarctic complex of species. Lieftinck (1966) provides excellent illustrations of E. cyathigerum and E. deserti, Garrison (1984) for E. annexum (labeled as E. cyathigerum) and Samraoui et al. (2002) discusses and figure differences between E. cyathigerum and E. risi. We illustrate examples of the right cercus in mediodorsal view of the taxa listed above without determining whether they represent specific or subspecific taxa. The cercus of E. tobagoensis is like that for the six taxa listed above in having a “finger-shaped, inwardly pointing subapical tooth, and an overhanging apical lip (Samraoui et. al. 2002).” However, the distal pale apical lip of the cercus in mediodorsal view in E. tobagoensis is transverse, extends across the entire distal margin of the cercus, and extends well beyond the glabrous tooth (Fig. 11). In the other six taxa, the pale apical lip is shorter, and is confined to the area directly posterior (E. annexum, Fig. 5; E. vernale, Fig. 10) or posterior and ventral (E. c. cyathigerum, Fig. 7) or ventral (E. circulatum, Fig. 6; E. c. risi, Fig. 8; E. deserti, Fig. 9) to the glabrous tooth. Enallagma tobagoensis is smaller than any of the other taxa associated with the E. cyathigerum complex and is the most melanic species of the group. The smaller size of E. tobagoensis is reflected in the reduced wing venation: RP 2 in Fw of E. tobagoensis arises at the fourth Px while in the other six taxa, RP 2 in Fw normally arises at the fifth Px.
Discussion
Due to the similar morphology among E. tobagoensis, E. annexum, and E. cyathigerum, the question naturally arises whether E. tobagoensis might be an adventive or derivative type of E. cyathigerum or E. annexum that may have been introduced in Tobago resulting in an altered phenotype as shown here. However, due to the differential morphology of the male cerci from E. cyathigerum and E. annexum, we believe that its smaller size, darker coloration, morphological differences enumerated above, and apparent endemicity to the neotropical region (Tobago) justify its description as a new species. No other member of the E. cyathigerum complex is known from the pantropical regions although D’andrea & Carfi (1994) report a pair of E. deserti from Ghana which may be an adventive or relict population, but further collecting will be necessary to establish its existence there. Our species appears to be rare and repeated attempts at resampling the species at its type locality and elsewhere on the island were not successful. Further collection of males and discovery of its female should help determine its status.
The island of Tobago, from a geological standpoint, runs roughly in a south-west to north-east orientation, and is defined primarily by a ridge of low mountains running along the length of the island, with only a few hundred meters of flat land between the foot of the mountain and the sea, and with no foothills in between. The type locality of our new species was a small, medium-gradient stream with a sand-gravel bed, at an abrupt transition from a steep, rocky, forested stretch to a short, sand-bedded, meandering stretch that reaches the ocean only a few hundred meters from the foot of mountain. Such streams are characteristic of the entire north-west facing coast of the island. The immediate area in which the two specimens were captured is a grassy pasture bordering the inland side of the coast road, just a few km northeast of the village of Castara, at the point where the forest ends and the pasture begins. Other species typical of such sites include Argia oculata Hagen in Selys, Argia translata Hagen in Selys, Erythrodiplax fusca (Rambur), and Dythemis s. sterilis Hagen.
description: Published as part of Donnelly, Thomas W. & Michalski, John, 2025, A new species of Neotropical Enallagma Charpentier of the cyathigerum complex from Tobago (Odonata: Coenagrionidae), pp. 383-388 in Zootaxa 5604 (3) on pages 383-387, DOI: 10.11646/zootaxa.5604.3.10, http://zenodo.org/record/15035727