Ceratocombus (Xylonannus) stysi, 2019

Roca-Cusachs, Marcos, Kim, Junggon, García-Becerra, Rafael & Jung, Sunghoon, 2019, Journey to the Center of the Earth: Description of a new troglomorphic litter-bug species inhabiting lava tubes in the Canary Islands (Heteroptera: Dipsocoromorpha: Ceratocombidae), Zootaxa 4550 (4), pp. 557-564 : 559-562

Ceratocombus (Xylonannus) stysi sp. nov. Roca-Cusachs, García-Becerra & Jung

Type Material: Holotype: CANARY ISLANDS, LA PALMA: Mazo, Llano los Caños. 1M. 15.I.1995. [Dry mounted] CRBA (CRBA-78277) . Paratypes: CANARY ISLANDS, LA PALMA: Mazo, Cueva del Llano de los Caños. 6 exx. 15.I.1995 alcohol CNU; 4 exx. 15.I.1995, in Alcohol. In RGB; 3 exx. 19.IX.1995. Dry mounted. In RGB; Barlovento, Cueva del barranco de la Grilla, 2 exx. 23.VII.2009. In Alcohol. CNU; Puntagorda, Cueva de las Cáscaras, 1 ex. 24.XII.2000, Dry mounted. In RGB

Type locality: CANARY ISLANDS, LA PALMA: Mazo, Cueva del Llano de los Caños [ CAVE]

Diagnosis: This species is place in the subgenus Xylonannus based on the following characters: Lateral sides of pronotum without macrochets, bearing only short setae, males and females with 2-segmented tarsi. The new species differs from other Ceratocombus (Xylonannus) occurring in western Palaearctic as it has unique characters typically found in troglomorphic species: total or nearly total reduction of the eye pigment; absence of pigment and colouration in the body and extreme long setae on antennae, legs and head. Hemelytra with no clear veins but only intuitive cells made by the dorsal vestiture of the corium. Parameres with a truncate apex with a small, acute, directed inwards, triangular process absent in any other congener, laterotergites VIII are also more slender and elongate, not spatulate at end but slightly acute.

Description: Male: Body entirely pale brown, depigmentated, 1.39–1.41 mm, elongated, covered with transparent setae. Head: elongated triangular, length of head as wide as width, distinctly longer than vertex width; compound eyes small, shorter than width of first antennal segment ( Fig. 1a ) vestigial, without visual pigment ( Fig. 2a, b, e & f ); ocelli absent; antennae shorter than length of body, with distinctly long spines; first and second segments thicker than other segments, first segment as thick as second segment, second segment somewhat clavated, third segment as long as fourth segment ( Fig. 2d ); frons and labium with long sensory seta (cephalic trichobothria), with numerous setae projected forward; rostrum long, reaching midcoxa, proportion of first to fourth segments 0.06: 0.09: 0.34: 0.29. Thorax: pronotum trapezoidal, anterior width slightly narrower than posterior width, anterior calli of pronotum protruded ( Fig. 2c ); scutellum triangular, anterior width distinctly widened, lateral margin somewhat concave; hemelytra not covering whole abdomen, but not brachypterous, lateral margin rounded; veins not distinctly visible, but recognized by setae located along veins ( Fig. 3a &b ); Hind wings absent; legs with long spines, well-developed claws ( Fig. 2 g–l). Abdomen: longer than hemelytra; with long laterotergites VIII, slender and elongated, slightly curved subapically, tapering at apex ( Fig. 3c, d ). Parameres: symmetrical, rod shaped, truncate apex with a small, acute, directed inwards, triangular process ( Fig. 3e ).

Female: entirely pale brown, depigmentated, 1.37–1.38 mm. Head: as in male. Thorax: as in male except for much shorter hemelytra. Abdomen: much longer than hemelytra; without abdominal appendages.

Measurements (in mm): Male (n=2)/Female (n=2) Body length, head-apex of hemelytra: 1.3 9–1.41/1.37– 1.38; head length: 0.26–0.27/0.25–0.26; head width, including compound eyes: 0.28–0.29/0.27–0.28; 1st antennal segment length: 0.06–0.07/0.05–0.06; 2nd antennal segment length: 0.14–0.15/0.14–0.15; 3rd antennal segment length: 0.49–0.51/0.47–0.48; 4th antennal segment length: 0.50–0.51/0.45–0.47; mesal pronotal length: 0.24–0.27/ 0.23–0.24; basal pronotal maximal width 0.34–0.35/0.32–0.34; anterior scutellar width: 0.21–0.22/0.20–0.21; mesal scutellar length: 0.17–0.18/0.15–0.17; hindleg (femur: tibia: tarsus): 0.53–0.57:0.70–0.74:0.27–0.28/0.49– 0.51:0.69–0.72:0.25–0.26.

Etymology: The specific name stysi stands for Pavel Štys, colleague and specialist in the group. Adjective in genitive form.

Habitat description. Cueva Barranco de la Grilla [Cave], Fig. 1.1 & 1d (28.80641, -17.82697). Linear lava tube with North orientation. The tube length is 222.1 metres and is located in an area of Laurel subtropical forest at 896 masl. The lava tube is extremely humid and the floor of the tube is covered with small flat stones.

Cueva de las Cáscaras, Puntagorda, La Palma , Canary Islands. (Approx. 28.77359, -17.98444) Fig. 1.2 & 1c. Small cavity of 44.4 m with two openings, one of them of very small diameter. The plant community of the exterior is composed mainly by Canarian pine ( Pinus canariensis ), together with Cistus symphytifolius , almond trees ( Amygdalus communis ) and abandoned crops. The substrate is very compact with some isolate sparse stones, however there are two small areas with sandy-muddy substrate ( Fig. 1c ) ( García-Becerra & González, 2001).

Cueva del Llano de los Caños [Cave], Mazo, La Palma , Canary Islands (approx. 28.61648, -17.78610) Fig. 1.3 & 1e. The lava tube runs by the thermo-Canary, subhumid bioclimatic floor, with typical vegetation association known as Fayal-brezal with some Prunus lusitanica, Persea indica, Pinus canariensis and disperse Chamaecytisus prolifer . The cave is almost a linear tube with a length of 1,200 m and with several short branches. Known by the locals as its entry was used as a garbage dump, however the general habitat is not very disturbed. Temperature and relative humidity were recorded during all the study. The average temperature in the tube was around 15 ° C, with maximum of 22° C in August and September, and minimum of 11.5 ° C in January and February. The average humidity values were always above 90% across all tube. Some areas in the cave have numerous cracks where numerous roots can be observed ( García-Becerra & González, 1997; Peris-Felipo et al. 2016).

Biology: According to García-Becerra & González (1997) and García-Becerra’s personal field observations, the species appears to be active almost year round and throughout the entire caves. The species has always been found in the pit-fall traps baited with cheese. Microhabitat of the species can be seen in fig. 1c.

Distribution: This species is only known from caves. Found in the Northern, Eastern and western La Palma Island.

Remarks: Most of the congeners live in the leaf-litter, rotting bark, and mosses, which in some cases are ecosystems that could share some characteristics with the subterranean world. However, when comparing Ceratocombus stysi sp. nov. with the nearest described species, C. brevipennis , several of its traits, in our understanding, could be interpreted as adaptations to troglomorphism. Its eyes are extremely reduced, and tarsal segments are in relation, much longer that its congeners. In addition, most Dipsocoromorpha are frequently dull colored when alive, but their colouration fades away when preserved in ethanol or other aqueous media, however, their cuticle consistency does not change, and their body does not become transparent. All this set of characters are considered to be troglomorphic in many other arthropod taxa ( Klaus et al. 2013; Oromí et al. 1997) and therefore we suggest that this species should be treated as such.

Figures

FIGURE 1. a, Map of the Canary Islands. Arrow marks the North. b, Map of the Island of la Palma and photographs of the exterior of the caves. c, Interior of Cueva de las Cáscaras, microhabitat of the species. d, Exterior of Cueva del Barranco de la Grilla. e, Entrance to Cueva del Llano de los Caños. Localities are marked with a red circle; 1, Cueva del Barranco de la Grilla; 2, Cueva de las Cáscaras; 3, Cueva del Llano de los Caños.

FIGURE 2. Ceratocombus (Xylonannus) stysi sp. nov.: a, Male dorsal habitus. b, Male ventral habitus. c, line drawing of pronotum. d, antennae (scalebar 0.1mm). e, detail of eye. f, Female ventral habitus. g-h, Pro-, meso- and metatarsus from male. j-l, Pro-, meso- and metatarsus from female. Scalebar equals 1mm.. Arrows show position of eyes.

FIGURE 3. Ceratocombus (Xylonannus) stysi sp. nov.: a, right hemelytron. b, line drawing of right hemelytron. c, pygophore. d, appendage. e, parameres. Scalebar equals 0.1mm. Arrows show position of laterotergites VIII and parameres.