Cixius theseus Hoch & Aguín-Pombo, 2025

Cixius theseus Hoch & Aguín-Pombo sp. nov.

Figs 6 A, B View Figure 6 , 7 A – G View Figure 7

Material examined.

Holotype: Spain • male; Canary Islands, El Hierro, Municipality of Frontera, Camino de San Salvador, MSS ; 27.73294972, - 18.01168166; 28 Aug. 2007; H. López and P. Oromí leg. ( IPNA) GoogleMaps . Paratype: Spain • female; same data as holotype (50354 DZUL) GoogleMaps .

Additional material.

Spain • 1 nymph III instar, 3 nymph IV instar; same data as holotype ( IPNA) GoogleMaps .

Diagnosis.

Cixius theseus sp. nov. is similar to the other cavernicolous Cixius species from El Hierro, C. ariadne Hoch & Asche, 1993 and C. nycticolus Hoch & Asche, 1993 in habitus (degree of troglomorphy), body size, general configuration of the male and female morphology, but differs in several characters: Frons 2.3 × wider than medially high and not pustulate (vs. 1.5 × wider and pustulate in C. ariadne ); tegmen with Y-vein preserved (vs. reduced in C. ariadne ); in the male genitalia: caudal margin of anal segment medially incised (vs. rounded in C. ariadne ), genital styles with distal expanded part dorsally rounded (vs. dorsally produced in C. ariadne ), basal part of aedeagus (shaft) left laterally with a prominent longitudinal ridge (vs. without such a ridge in C. ariadne ), and with bifurcate ventral projection slender (vs. wide in C. ariadne ), right lateral subapical spinose process sturdy and in repose curved dorsally (vs. slender and in repose curved basally in C. ariadne ) and, most prominently, distal part of aedeagus (flagellum) with a slender spinose process at ca. midlength (vs. without such a spinose process in C. ariadne ); in the female genitalia: caudal margin of 7 th sternite medially expanding into an obtusely angulate process (as in C. nycticolus , vs. caudal margin straight in C. ariadne ), and wax-secreting field on 9 th tergite medially separated by a narrow, longitudinal, membranous area (vs. wax-secreting field medially not separated but with a distinct median ridge in C. ariadne and C. nycticolus ).

Description.

Habitus. Strongly troglomorphic with compound eyes absent, tegmina, wings and bodily pigmentation strongly reduced.

Body length. Male 2.7 mm (n = 1). Female 3.3 mm (n = 1).

Colouration. Male. Head and thorax incl. legs light yellowish, lateral carinae of head and posterior margin of vertex brownish; antennae whitish; tegmina translucent, whitish, venation white-yellowish, veins beset with brownish setae; legs whitish, distal spines of hind tibiae and of metatarsal joints brownish; abdomen whitish, genital capsule slightly darker, yellowish brown. Female. Head with vertex light yellowish, frons yellowish, medially with a brownish longitudinal stripe; clypeus light brown; antennae yellowish with distinct reddish brown star-shaped sensory plaque organs; pronotum medially, i. e., between lateral carinae, yellowish, lateral portions slightly darker, yellowish brown; mesonotum light yellowish; tegmina translucent, venation whitish, beset with brownish setae; legs yellowish white; abdomen light yellowish, genital segment incl. ovipositor yellowish brown.

Head. Vertex short, ca. 3.5 × wider at base than medially long, very faintly separated from frons by an obsolete transverse carina. Frons convex, ca. 2.3 × wider than medially high, lateral carinae distinctly ridged and directed (antero-) laterally; frons smooth, without median carina, not pustulate. Frontoclypeal suture highly vaulted / arched. Post- and anteclypeus smooth, without median carina, together ca. 3.4 × longer than frons. Rostrum elongate, 2 nd joint longest; rostrum relatively shorter in the male: surpassing caudal margin of hind coxae only slightly, in the female with ca. half the length of 3 rd joint. Compound eyes and ocelli absent. Antennae with scape very short, ring-like, pedicel subcylindrical, ca. 1.4 × longer than wide, in the female with distinctly recognizable star-shaped sensory plaque organs.

Thorax. Pronotum faintly tricarinate, lateral carinae diverging laterally, gradually vanishing; pronotum ca. 1.8 × wider than maximum width of head, and 4.2 × wider than medially long, posterior margin concave, obtusely angulate. Mesonotum tricarinate, carinae only faintly recognizable, lateral carinae reaching posterior margin, median carina feeble, obtuse, vanishing caudally; mesonotum in the male 1.5 ×, in the female 1.4 × wider than medially long, and in midline 2.3 × longer than length of pronotum. Tegulae small. Tegmina strongly reduced, their caudal margin attaining ca. midlength of 3 rd abdominal tergite; tegmen longer than maximally wide: ca. 1.5 × in the male, and 1.65 × in the female; venation rudimentary, costal vein strong, basal cell closed, „ Y-vein “ (Pcu, A 1, Pcu + A 1) preserved and recognizable, A 1 and Pcu + A 1 very close to posterior margin of tegmen; tegmina with numerous conspicuous setae along veins. Wings vestigial, very small.

Metatibiae laterally with 3 tiny spines, distally with 6 (in the male), and 6 / 7 (in the female) apical teeth, of which the lateral one is largest. First metatarsal joint in both sexes with 4, and second metatarsal joint with 4 (in the male) and ¾ (in the female) distal spines. First metatarsal joint about as long as 2 nd and 3 rd metatarsal joints together. Pretarsal claws slender, arolium small.

Male genitalia. Genital segment in caudal aspect slightly higher than wide, medioventral process simple, in ventral aspect obtusely angulate. Anal segment in dorsal aspect rectangular, ca. 2 × longer than wide, with distal portion slightly bent ventrally, lateral margins parallel, distal margin medially incised. Genital styles slender at base, distally expanding dorsally, expanded part medially concave. Aedeagus with basal part (shaft) slender, more or less tubular, left laterally with a prominent, longitudinal, rounded ridge and ventrally with a bifurcate projection directed basally. Shaft subapically on its right side with a sturdy movable spinose process which in repose is curved basally, its tip pointing dorsally. Distal part of aedeagus (flagellum) tubular, in repose bent dorsally and to right side, surpassing midlength of shaft, with a slender, spinose process, in repose directed basally, left laterally at ca. midlength of flagellum; visible part of ejaculatory duct rugose; phallotreme wide, located apically.

Female genitalia. 7 th sternite with anterior margin convex, highly vaulted cephally, rounded, caudal / posterior margin medially expanding caudally, expanded portion obtusely angulate. Ovipositor ensiform, slightly curved dorsally, caudally surpassing anal tube with less than 1 / 3 of its total length; anal segment tubular, short, in lateral view ca. 2 × higher than long, lateral margins more or less parallel; 9 th tergite caudally truncate, wax-secreting field distinctly limited, slightly concave, medially separated by a narrow, longitudinal membranous portion.

Etymology.

The species epithet is a noun in nominative singular and refers to Theseus, one of the heroes in Greek mythology, friend of Ariadne. The gender is masculine.

Distribution.

Adults known only from the type locality (Camino San Salvador), in the laurel forest in the huge landslide of El Golfo, at the northwest of El Hierro (Fig. 1 View Figure 1 ). Endemic to El Hierro.

Ecology and behaviour.

El Hierro is the youngest island in the Canary archipelago, and the youth of the terrain is visibly apparent in much of its territory. Fields of recent lava abound, and a large part of the soil is made up of volcanic deposits where fine ash or more or less coarse lava clinker predominate, or a mixture of both in highly variable proportions. In the central, western, and northern parts of the island, it is very common to find terrains formed by a layer of lava clinker covered by fine ash or an already formed, thin edaphic soil. The scoria layer contains a dense network of interstices and cracks (Fig. 2 View Figure 2 , top right), well isolated from changes in humidity and temperature from the outside by the overlying fine pyroclasts or soil covering it. This type of MSS was described for the first time in El Hierro and named as “ volcanic MSS ” ( Oromí et al. 1986). Under these circumstances, the layer of pyroclasts maintains a high humidity level and a rather constant temperature throughout the year, which allows for the establishment of fauna adapted to subterranean life. This configuration of volcanic deposits constitutes the most common type of MSS in El Hierro, extending across large areas of the island. In Camino de San Salvador, where Cixius theseus n. sp. was discovered, the MSS was exposed when the terrain was cut to build a road (Fig. 2 B View Figure 2 ). The location is in the laurel forest whose dominant trees are Morella faya (Aiton) Wilbur and Erica canariensis Rivas-Mart., Osorio and Wildpret , and herbaceous plants in the vicinity of the traps are Pericallis murrayi (Bornm.) B. Nord. and Urtica morifolia Poir. The traps were set over the talus of the road crossing the laurel forest, at 1230 m a. s. l. Although a good representation of the entire troglobiont fauna present on the island has been collected in nearby areas using MSS traps, only the capture of this new cixiid species should be noted in Camino de San Salvador.

Ecological classification. Cixius theseus displays a high degree of troglomorphy: compound eyes and ocelli absent, tegmina strongly reduced, vestigial wings as well as light, almost white body coloration. This blind and flightless species is most likely restricted to subterranean environments throughout its entire life cycle. According to the criteria provided by Sket (2008) and Howarth and Moldovan (2018 a, b) we regard Cixius theseus as an obligate cavernicole, or troglobiont.

Conservation status.

Although only a few individuals of Cixius theseus are known, this new species apparently would not have conservation problems for several reasons: i) the volcanic MSS is widely distributed throughout the northern slope of the island, so habitat availability is not a limiting factor; ii) in general, this entire slope of the island with laurel forest is well-preserved and there are no houses that could be contaminating the subsurface with sewage; iii) since cixiids feed by sucking fluids from roots, the presence of laurel forest in high density across this area ensures a constant food supply. The initial results from the MSS traps in San Salvador showed very poor capture of troglobitic species, which led us to their deactivation soon, a reason why very few specimens of this new species are known. However, Cixius theseus also clearly meets criterion D 2 as in the case of Cixius palmirandus , so it should be classified as Vulnerable according to the IUCN criteria.

Remarks.

From the type locality, 4 unpigmented, eyeless cixiid nymphs (III. and IV. instar) were collected, which are here preliminarily identified as C. theseus sp. nov. ( IPNA). Morphologically very similar nymphs have been recorded from another locality („ Mercader, MSS 4; 27 Jan. 2012; H. López leg. “ and „ Mercader, MSS 3; 18 Jun. 2012; P. Oromí and H. López leg. “), 1075 m a. s. l. (27.71294456, - 18.02217521), on the southern slope of the island, 2.3 km far from San Salvador. Whether these are conspecific with C. theseus cannot be confirmed on the basis of morphological characters alone. It remains to be investigated whether C. theseus sp. nov. is more widely distributed on El Hierro.