Nesobasis delai, Marinov & Rashni, 2025

Marinov, Milen & Rashni, Bindiya, 2025, A contribution to the Odonata fauna of Moala Island, Fiji. Part I: erection of three new species in genera Nesobasis Selys, 1891 and Nikoulabasis Ferguson et al., 2023 (Odonata: Coenagrionidae), Zootaxa 5637 (2), pp. 292-310 : 294-296

Nesobasis delai sp. nov.

( Figs 2–3 )

Holotype. ♂ ( NZAC04231103 ), headwater system, a tributary of Waitabu Lake , 18.5947S, 179.8700E, 413 m a.s.l., 26 October 2020, DR leg.

Paratype. 1♂ ( USPac_14002 ), Wailevu Creek under the Savukaratu waterfall above Maloku village , 18.5903S, 179.8744E, 260 m a.s.l., 4 May 2024, MM leg .

Etymology. The name refers to the fact that both male specimens were collected from higher sections of the water courses on the island; Fijian word “ delai ” [= hilltop]. The name is a noun in apposition.

Description of holotype

( Fig. 2 )

Head ( Fig. 2B–C ). Labium pale—white posteriorly and yellow anteriorly; genae yellow-green around the bases of mandibles continuing to the tips of the latter (except for a brown spot at the level of the border between labrum and anteclypeus) and the anteclypeus; labrum dark yellow with a wide brown bar at the base; remainder of face bluish on almost entire surface of the genae up to base of the scape, going transversely towards each other on the frons along base of postclypeus interrupted by a black bar at middle of frons; postclypeus black; black on remainder of the head down to rear part up to a yellow area close to the posterolateral corners of labium with light areas as follows: yellow anteriorly of the median ocellus, yellow triangular spot on anterior faces of toruli and dorsal corners of scape; pedicel brown, flagella missing; eyes discoloured.

Thorax ( Fig. 2A–B ). Prothorax entirely black with white pruinescence ventrally on middle lobe, posterior lobe raised up. Pterothorax predominantly black on mesothoracic segments with blue as follows: spindle-shaped spot along the mesopleural suture, spot at dorso-posterior end of mesepimeron, ventral 1/3 rd of mesinfraepisternum; metathorax predominantly blue with black as follows: inverted “C” at the posterior end of metepisterunum, rim around metathoracic spiracle and tiny spot at the dorso-anterior corner, dorso-posterior corner of metinfraepisternum; faint line along the dorsal corner of mesinfraepisternum. Legs: coxae bicoloured yellow anteriorly with posterior faces black on prolegs and pale blue on the other legs; trochanters yellow; femora yellow anteriorly and black posteriorly; colouration on the tibiae reversed (dark inner and pale outer faces) with small brown spots on the yellow areas at the bases and the tips; tarsi dark yellow becoming darker brown at the tips; mesostigmal plate with stout widely rounded tubercle at the dorso-posterior corner, black with pale on the top of the tubercles.

Wings ( Fig. 2D ). Venation black; pterostigma entirely black in FW, black with pale line along the costal edge at anterior corner; FW: 16 Px, RP 2 at 6 th Px; HW: 14 Px, RP 2 at 5 th Px; arculus at 2 nd Ax in FW and slightly distal in HW.

Abdomen ( Fig. 2A ). Black on entire dorsum and most of lateral surfaces of all segments; blue on the ventral half of S1 tergum, posteriorly on S2, spots on S9; dark yellow on ventral edges of tergal segments S3–6; sterna mostly dark—yellow anteriorly and brown posteriorly becoming black towards the end, pruinescence on S8. Cerci ( Fig. 2E–F ) pincer-like black in colour with ventral expansions pale dorsally and dark ventrally; paraproct dark brown scarcely projecting beyond the posterior edges of S10. Penis ( Fig. 2G–H ): distal segment T-shaped with sides tapering towards the tip, laterally swollen and arched with a large spine underneath.

Measurements: AL 37.5, HW 24, HF 2.3, S 0.2, P 0.3, MDBE 1.56.

Variations of paratype

The single male paratype has been discoloured and the chromatic variations were assessed based on the overall body pattern. Figure 3 presents the most significant differences observed on the thorax. Black occupies larger areas along the interpleural suture with the marking on the metepisternum connected to the dark are on the mesepimeron. Dark patches developed in between mid- and hind coxae, ventro-anterior corner of metinfraepisternum and posterior end of metepimeron. The latter present on both sides of the thoracic capsule, however, it may be a postmortem effect with the live individuals probably having the entire segment blue as indicated on the body of the holotype.

Measurements: AL 33, HW 21.5.

Differential diagnosis

The shape of cerci, measurements of antennal segments and length of legs classify males of N. delai as a member of the so called longistyla -group of taxa following the convention given in Donnelly (1990) and idiognosis provided in Donnelly & Marinov (2024: 155). Males of N. delai have a unique combination of characters which reviewed individually would bring them closer to any member of the group (apart of N. caerulescens Donnelly, 1990 known by females only). The penis structure (T-shaped distal segment) is typical of N. campioni Tillyard, 1924 , N. monticola Donnelly, 1990 , and N. nedeltshevae Marinov & Rashni, 2023 . The transverse bar of the “T” resembles N. nedeltshevae most, but the tapering shape of this segment and the large spine underneath is similar to the structure of N. monticola . However, in N. delai the segment looks larger and arching in lateral view as opposed to almost flat in N. monticola . In dorsal view the cerci are very close or almost identical to N. caerulecaudata Donnelly, 1990 and N. longistyla Selys, 1891 . Males of N. delai can be distinguished by the ventral inner expansion which occupies ¾ of the length as opposed to extending slightly more than halfway in the other two. General body colouration of N. delai (predominantly black with blue) is closest to N. longistyla especially in the abdominal pattern and pruinosity of the thorax and black markings on the metepisternum (e.g. fig. 173A–B in Donnelly & Marinov 2024: 176), but the thorax of N. delai lacks the black area along the metapleural suture (present in most of N. longistyla variations) and has a characteristic marking along the interpleural suture (see Fig. 2B ).

Figures

FIGURE 2. Nesobasis delai, holotype: A) habitus; B) head and thorax, dorsal and lateral view; C) head, frontal view; D) HW; E–F) appendages, dorsal and lateral views; G–H) penis, lateral and ventral views.

FIGURE 3. Nesobasis delai, thoracic pattern of the male paratype.