Tachycixius gomerobscurus Hoch & Oromí, 2025

Hoch, Hannelore, López, Heriberto, Naranjo, Manuel, Aguín-Pombo, Dora & Oromí, Pedro, 2025, Endless forms most wonderful: Four new cavernicolous planthopper species (Hemiptera, Fulgoromorpha, Cixiidae and Meenoplidae) from the Canary Islands, Subterranean Biology 51, pp. 61-101 : 61-101

Tachycixius gomerobscurus Hoch & Oromí sp. nov.

Figs 8 A, B , 9 , 10 A – G

Material examined.

Holotype: Spain • male; Canary Islands, La Gomera, Reventón Oscuro, MSS T 3; 28.12468504, - 17.21638908; 2 Jan. 2012; P. Oromí leg. (50355 DZUL) .

Paratypes: • Same data as holotype, except • 1 male, 1 female; 5 Feb. 2009; P. Oromí and H. López leg. (34924 DZUL) • 1 male (6962 DZUL), 2 males (7014 DZUL), 3 males (7074 DZUL); 30 Jun. 2009; P. Oromí and H. López leg. • 1 male; 1 Jul. 2009; P. Oromí and H. López leg. (34935 DZUL) • 2 males; T 3; 4 Jan. 2010; P. Oromí leg. (7009 DZUL) • 1 female; 8 Jun. 2010; P. Oromí and H. López leg. ( UMACI) • 1 male, 1 female; T 1; 9 Jan. 2011; P. Oromí and H. López leg. ( UMACI) • 1 male, 3 females; T 1; 30 Jul. 2011; P. Oromí leg. ( IPNA) • 1 male, 1 female; T 3; 2 Jan. 2012; P. Oromí leg. (7038 DZUL) • 1 male, 1 female; T 3; 26 Mar. 2015; P. Oromí leg. ( UMACI) • 1 female; 17 Sep. 2015; P. Oromí leg. ( DZUL) • 1 male; 31 Jul. 2024; P. Oromí leg. ( IPNA: BC 3166 ) .

Additional material.

• Same data as holotype, except • 3 nymphs V instar (6962 DZUL), 4 nymphs V instar; T 1; 30 Jul. 2009; P. Oromí and H. López leg. ( UMACI) • 3 nymphs V instar and 1 nymph IV instar; T 3; 4 Jan. 2010; P. Oromí leg. ( UMACI) • 1 nymph V instar and 1 nymph IV instar; T 3; 8 Jul. 2010; P. Oromí and H. López leg. ( UMACI) • 1 nymph V instar; 9 Jan. 2011; P. Oromí and H. López leg. ( UMACI) • 1 nymph V instar; T 1; 30 Jul. 2011; P. Oromí leg. ( IPNA: BC 2984 ) • 2 nymphs IV and V instar; T 3; 2 Jan. 2012; P. Oromí leg. ( IPNA: BC 2982 , BC 2983 ) • 1 nymph V instar; T 1; Jun. 2013; P. Oromí leg. ( UMACI) • 2 nymphs III and IV instar; T 1-4; 17 Nov. 2013; P. Oromí leg. ( IPNA: BC 2985 , BC 2986 ) • 1 nymph V instar; 17 Sep. 2015; P. Oromí leg. ( UMACI) • 1 male; 31 Jul. 2024; P. Oromí leg. ( IPNA: BC 3165 ) .

T 1, T 2, T 3 are the different MSS traps set along ca. 100 m in the same location.

Diagnosis.

In general appearance and in the overall configuration of male and female genital structures Tachycixius gomerobscurus sp. nov. ressembles T. crypticus and T. retrusus from Tenerife, but differs in the following characters: shape of vertex: vertex short, anterior margin very shallowly rounded (vs strongly convex towards frons in T. crypticus and T. retrusus ); colouration of tegmina: less vividly coloured than in T. crypticus and T. retrusus ; reduction of hind wings much stronger than in T. crypticus and T. retrusus ; male genitalia: caudal margin of anal segment medially strongly concave (vs shallowly concave in T. crypticus and straight in T. retrusus ); shaft of aedeagus with 3 subapical movable spines (vs. 2 such spines in T. crypticus and T. retrusus ); female genitalia: 9 th tergite medioventrally deeply incised, membranous excavation acutely triangular (vs 9 th tergite medioventrally only shallowly incised, membranous excavation dorsally shallowly rounded in T. crypticus and T. retrusus ); 9 th tergite with wax-secreting field medially with a short, but distinct median ridge (vs without such a ridge in T. crypticus and T. retrusus ).

Description.

Habitus. In general appearance resembling Tachycixius crypticus Hoch & Asche, 1993 and T. retrusus Hoch & Asche, 1993 from Tenerife, although less vividly coloured; weakly troglomorphic (i. e. hypogeomorphic, see Deharveng and Bedos 2018): compound eyes present, but small, tegmina covering most of the abdomen but not attaining tip of anal tube in the male, respectively tip of ovipositor in the female; hind wings strongly reduced, vestigial.

Body length. Male 3.8–4.05 mm (n = 4). Female 4.3–5.2 mm (n = 6).

Colouration. Vertex, frons and head laterally light yellowish, with lateral carinae of vertex and frons and posterior margin of vertex slightly darker; antennae (pedicel) whitish; compound eyes reddish-dark brown; pro- and mesonotum light yellowish, otherwise thorax incl. Legs whitish, tips of lateral and distal spines of tibia, as well as distal spines of first and second metatarsal joints dark brown. Tegmina translucent, light yellowish, venation whitish, bases of setae along veins and margin of tegmen slightly darker, brownish; tegmen with anterior portion of triangle formed by cubitus posterior (CuP) and posterior margin of tegmen profusely brownish, and three irregularly limited, faint fuscous transverse bands: one at level of tegmen midlength, one at level of pterostigma, and one more or less parallel to distal margin (see remarks). Abdomen incl. genitalia light yellowish, or yellowish-brown, respectively.

Head. Vertex short, about 3.5 × wider at base than medially long, anteriorly rounded, with a faint median carina, areolets small, slightly concave, medially separated by an obtuse median carina; vertex indistinctly separated from frons by an obsolete transverse carina. Frons 1.2 × wider than medially high, with a distinct median carina, lateral carinae foliately produced laterally. Post- and anteclypeus with an obtuse median carina; together ca. 1.5 × longer than frons. Frontoclypeal suture strongly arched. Compound eyes present, compared to epigean Tachycixius species reduced in relative size, pigmented, lateral ocelli distinct, median frontal ocellus rudimentary. Rostrum elongate, well surpassing hind coxae, in males attaining anterior margin of 9 th abdominal segment, in females attaining level of caudal margin of 9 th tergite. Antennae with scape short, ring-like, and pedicel cylindrical, ca. 1.4 × longer than wide, with sensory plaque organs arranged in several rows.

Thorax. Pronotum tricarinate, lateral carinae ridged and diverging laterally near posterior margin of pronotum; pronotum short, medially ca. 1.8 × longer than vertex, and 1.7 × wider than maximum width of head (incl. compound eyes), posterior margin concave, medially forming an obtuse angle. Mesonotum tricarinate, carinae faint, lateral carinae attaining posterior margin of mesonotum; mesonotum 1.2 × wider than medially long, and medially 3.2 × longer than pronotum. Tegulae small. Tegmina distally reduced, in both sexes attaining caudal margin of anal segment, ca. 2.5 × longer than maximally wide; venation well developed, variable among specimens (in all specimens studied except for 1 female, the CuP vein does not connect to posterior margin of tegmen as is the case for most Cixiidae , but merges with PCu + A 1 (= common stem of Y-vein, see Fig. 6 , arrow), see remarks; basal cell closed, pterostigma faintly recognizable; veins beset with or accompanied by numerous conspicuous bases of setae, on distal margin also between veins. Hind wings very small, vestigial, not surpassing posterior margin of metanotum. Metatibiae laterally in the majority of specimens studied with 3 small spines (variation: configurations 4 / 3 and 3 / 2 were observed in one female each), distally with 6 sturdy spines (in one female with 7 spines on one leg) (arranged in a row, lateral one strongest); metabasitarsus distally with 7–8 (bilaterally and individually variable), 2 nd metatarsal joint distally with 7–8 spines (bilaterally and individually variable), each of the median 4 bearing one macroseta. Metabasitarsus slightly longer than 2 nd and 3 rd metatarsal joints together. Pretarsal claws short, stout, arolium small.

Male genitalia. Genital segment in caudal view ca. 1.3 × higher than wide, and in lateral view ventrally ca. 4.6 × longer than dorsally, caudal margins laterodorsally produced into 2 rounded lobes directed laterocaudally; medioventral process slender, triangular, dorsal surface with a faint median ridge. Anal segment elongate, narrow, in distal third bent ventrocaudally, in dorsal view ca. 2 × longer than wide at base, lateral margins in dorsal view more or less parallel, caudally of anal style converging, distal margin broadly rounded, ventral portion distally of anal style in caudal aspect strongly vaulted, with caudal margin medially concave; anal style elongate, slender. Genital styles narrow at base, distal third expanding dorsally, expanded portion caudally rounded, dorsally with an obtuse angle, medially concave. Aedeagus. Basal part of aedeagus (shaft) in proximal half wide, with three more or less compressed velum-like projections: one left laterally, extending from base to ca. midlength of shaft, one ventrally which is wide at base, narrowing at ca. midlength of shaft and extending from base almost to apex, and one right laterally which is broadly rounded and directed right laterocaudally. Shaft in distal half on right side with a compressed lobe extending right laterally, and subapically with 3 sturdy movable spinose processes: one left laterally, in repose curved dorsally, one ventrally, in repose directed basally, its tip pointing left laterally, and one right laterally, which is double-S-shaped, in repose curved basally and to right side. Distal portion of aedeagus (flagellum) well surpassing midlength of shaft, medially almost rectangularly bent and directed right laterally; without any spinose processes; distal portion of flagellum on ventral side expanding into a lobate, rounded protrusion, visible part of ejaculatory duct rugose, phallotreme wide, exposed dorsally.

Female genitalia. Seventh sternite subtriangular, anterior margin broadly rounded, caudal margin medially straight; ovipositor ensiform, slightly curved dorsally, caudally slightly surpassing anal segment; anal segment tubular, short, stout, dorsoventrally only slightly depressed; ninth tergite caudally truncate, wax-secreting field indistinctly limited, shallowly concave, with a short, but distinct median ridge; 9 th tergite medioventrally deeply incised, membranous excavation acutely triangular, attaining dorsal third of 9 th tergite.

Etymology.

The species epithet is an adjective in nominative singular and a combination of Gomera and oscuro, the Spanish word for dark, probably used to create the toponym of this shadowy location inside the laurel forest. The gender is masculine.

Distribution.

Known only from the type locality, Reventón Oscuro, municipality of Hermigua, in Garajonay National Park (Fig. 1 ). Endemic to La Gomera.

Ecology and behaviour.

The MSS in Reventón Oscuro and in other places of Garajonay National Park is of the colluvial type, originated by accumulation of stone fragments at the base of rocky walls, and covered over time by soil ( Juberthie et al. 1980, Mammola et al. 2016). The three traps set in Reventón Oscuro are on a steep slope inside a dense, humid and moderately dark laurel forest at 1035 m a. s. l. with a thin but rich organic soil covering the colluvium. All traps were set very close to tree trunks in order to protect them from gravitational collapse, and the colluvium was rich in small roots throughout its sampled depth (70–80 cm). La Gomera is the only island of the archipelago without lava tube caves due to the absence of volcanism in the last 2.5 Ma, but the MSS in the laurel forest is rich in troglobionts ( Medina and Oromí 1990, Pipan et al. 2010, Gilgado et al. 2011, García et al. 2020). In this sense, Reventón Oscuro is the most diverse (13 species) among all Canary Island’s MSS stations, as well as the most abundant in individuals (PO, HL unpublished data).

Ecological classification. Tachycixius gomerobscurus displays several troglomorphic characters, although not as strongly as Tachycixius lavatubus Remane & Hoch, 1988 , Cixius palmirandus or C. theseus : the integument shows remnants of brownish pigmentation, the compound eyes are reduced in size, yet present, and ommatidia are pigmented; the lateral ocelli are distinct, the frontal ocellus is rudimentary. The tegmina are reduced distally, and hind wings are vestigial, much shorter than in the other MSS-dwelling species T. crypticus and T. retrusus . Although there are no observations on the behaviour of the species, we assume that individuals are unable to fly, but may be able to perceive visual input. As T. gomerobscurus has been collected from traps in the MSS, and given the presence of reduced but pigmented eyes, little is known about its behaviour. Despite its comparatively mild degree of troglomorphy, we assume that T. gomerobscurus is restricted to subterranean environments, and we therefore regard it preliminarily as an obligate hypogeomorphic troglobiont.

Conservation status.

Over the past 15 years, nearly 40 individuals (both adults and nymphs) of this new species have been collected using MSS traps baited with liver or blue cheese. These individuals probably fell into the traps by chance rather than being attracted to the bait, as these planthoppers feed by sucking fluids from roots. The MSS site of Reventón Oscuro is the location in the Canary Islands where we have captured the largest number of troglobitic planthoppers using MSS traps, and the number of captures has remained relatively constant over the years. All evidence suggests that this species likely has a high density of individuals in this area. The region where this new species has been collected is a very well preserved national park, where a dense laurel forest ensures a consistent food supply in the subterranean habitat (roots). The limited known distribution of T. gomerobscurus on La Gomera is primarily due to the scarce sampling performed in the MSS at other sites on the island, being uncertain whether or not it has a broader distribution. However, although this species lives in a well-preserved habitat where it could apparently have a good population size, the IUCN recommends classifying it as Vulnerable according to criterion D 2, since only one population is known distributed in a small area, which could completely disappear or enter a higher threat category if such a limited area were suddenly affected by impacts of human activities and / or stochastic events.

Remarks.

The peculiar venation pattern observed in all but one specimens studied (the CuP merging with PCu + A 1, i. e., the common stem of the „ Y “ - vein instead of connecting to the posterior margin of tegmen) is very unusual not only for Cixiidae , but the Fulgoromorpha. It is likely a mutation in connection with the distal reduction of the tegmen, which has affected the overall venation pattern.

Some variation is observed in the colouration of body and tegmina: 2 specimens, 1 male and 1 female (coll. 2 Jan. 2012; T 3) show very weak pigmentation of body and tegmina, and appear to have freshly molted into adult.

Figures

Figure 1. The Canary Islands and distribution of the new species described. Black triangle: Cixius palmirandus Hoch & Naranjo, sp. nov.; Black circle: Tachycixius gomerobscurus Hoch & Oromí, sp. nov.; Black stars: Cixius theseus Hoch & Aguín-Pombo, sp. nov.; Black square: Meenoplus skotinophilus Hoch & López, sp. nov. (https://commons.wikimedia.org/wiki/File:Map_of_the_Canary_Islands.svg; https://catalogo.idecanarias.es/geonetwork/srv/spa/catalog.search#/metadata/spagrafcan_MTLWMS_20160101).

Figure 6. Cixius theseus Hoch & Aguín-Pombo, sp. nov. A habitus male (holotype) B habitus female (paratype). Scale bar: 0.5 mm.

Figure 8. Tachycixius gomerobscurus Hoch & Oromí, sp. nov. A habitus male B head and thorax, dorsal aspect.

Figure 9. Tachycixius gomerobscurus Hoch & Oromí, sp. nov. Right tegmen (male). For meaning of arrow see text. Scale bar: 0.5 mm.

Figure 10. Tachycixius gomerobscurus Hoch & Oromí, sp. nov. Male genitalia A genital segment, caudal aspect B same, ventral aspect C anal segment, caudal aspect D left genital style, maximum aspect E anal segment, genital segment, aedeagus and genital styles, in situ, left lateral aspect F aedeagus, right lateral aspect G same, ventral aspect. Scale bar: 0.1 mm.