Opisthjapyx naledi Sendra & Sanchez-Garcia 2023, sp. nov.

Epicuticle smooth under optical microscope; with few micropores visible at higher magnifications (dorsal side of urite X with 1 micropore per 10 μm 2, diameter 0.6‒0.7 μm) (Fig. 21B). Cuticle unpigmented with slightly sclerotized areas on dorsal frontal head, mandible tips, femoral and tibial condyles, abdominal segments VIII−X, and cerci. HEAD.

Antenna length 9.5 mm, 0.35× length of body, with 49 antennomeres; basal antennomere short, followed by two slightly longer antennomeres; antennomeres I−IV with reinforced borders visible on ventral side (Fig. 16C); medial antennomeres 1.1× wider than long (Fig. 16B). All antennomeres with M and a few ms setae, plus three whorls of mbsM (Fig. 16A‒C). Trichobothria present on antennomeres IV‒VII in a 3/4/4/4 pattern, with a trichobothria in central position (Fig. 16C).

Apical antennomere with 16‒18 placoid sensilla distributed in three irregular groups; penultimate antennomere with two placoid sensilla (Fig. 16A‒B). Dorsal and ventral side of head with abundant sM and ms uniformly distributed and apparently without M (Fig. 17A); on ventral side: submentum with 2+2 M in anterior position plus 2+2 M in posterior position, admentum with 3+3 M, mentum at base of labial palps with 1+1 M; external lobes of mentum with abundant sM and the pair of exertil vesicles visible (Fig. 18A).

Labial palp short, length 0.24 mm, 3.2× as long as wide, with one proximal sM and four medial and distal sM plus several ms. Lacinia falciform, well sclerotized, all five laminae large and pectinate. THORAX.

Thoracic segments elongate, with extra M, several sM, and abundant ms uniformly distributed. Pronotum with 5+5 M1−5 plus extra 6+5 M; prescutum of mesonotum with 1+1 M; mesonotum with 5+5 M1−5 plus extra 4+4 M; prescutum of metanotum with 1+1 M, metanotum with 5+5 M1−5 plus extra 4+4. (Fig. 17B‒D).

Thoracic sternites, intersternites, and presternites defined, with ms, sM and M (Fig. 18 A−D). Pro-presternites and pro-, meso- and metasternites with strong internal Y-shaped cuticular structures (furcisternites) (Barlet & Carpentier 1962), only in pro-presternites the prolongation of posterior branch (spine) is visible on the surface (Denis 1949). Pro-presternum with no clearly defined limits, spine with apparently 3+3 M and some sM; prosternum with about 70 M or sM well distributed in a variety of shapes; meso-poststernum with 10+10 M-sM; meso-intersternum with 7+7 M-sM; mesosternum with about 100 M-sM; meta-poststernum with 16+16 M-sM; meta-intersternum with 10+10 M-sM; and metasternum with about 160 M-sM.

Legs slightly short, hind leg 4.6 mm long, reaching third abdominal segment. Femur-tibia-tarsus articulations with a row of sM; coxa with 14 ventral M-sM; trochanter with 10 M-sM; femur with 24 ventral M-sM and 16 dorsal M-sM; tibia with 20 M-sM; tarsus with 30 M-sM plus two ventral rows of 5 and 6 thick setae. Pretarsus with two short, thick, unequal claws, and a rounded medial unguiculus.

ABDOMEN. Abdominal tergites with a few ms and sM plus several M or sM. Prescutum of urotergite I with 1+1 M, scutum with 1+1 M or sM (ma), 1+1 M1, 1+1 M5 and 2+2 medial intermediate M; urotergite II with 1+1 M(ma), 2+2 M1−2, 2+2 M4−5, 1+1 medial intermediate M and 1+1 lateral intermediate M; urotergites III−VII with 1+1 M or sM (ma), 5+5 M1‒5, 1+1 medial intermediate M and 1+1 lateral intermediate M; urotergite VIII with 2+2 M; urite IX with 12+12 ventral M (Fig. 19 A−D).

Urite X 1.5× as long as wide; with distinctly marked carinae; carinae with subparallel margins; dorsal side with 6+7 intracarinal D1−6 M plus 2+2 lateral M between D2, 1+1 medial M and 1+1 lateral M between D3, 1+1 lateral M between D3−4, and 3+3 M between D6; acropygium rounded; lateral side with 5 rows of 8−10 M; ventral side with 4+4 rows from lateral to central with 7−8 M (Fig. 21A‒D). All tergites with blunt, slightly rounded posterolateral angles (Figs 19 C−D, 20C‒D).

Urosternite I (Fig. 20 A−B) with scarce ms and abundant sM indistinct from M; sM more abundant at the narrow anterior portion of lateral subcoxal organ, with about 90 sM each. Median glandular organ with several tiny setae (Fig. 19E). Lateral subcoxal organ with three rows of short glandular setae (GS) (about 240 GS) and one posterior row of about 60 sensory setae (SS); lateral subcoxal organ occupying 0.36× of interstylar width/area; GS/st1 and SS/st1similar= 0.14 (Fig. 20A‒B); urosternites II‒VII with scarce ms and abundant sM undifferentiated from the thick and bunt apex shape M (Fig. 20C‒D).

Cerci asymmetric, strong, well-developed, length 1.4 mm, rectilinear along the proximal half and curved in the distal half, becoming a large hook towards apex; heavily sclerotized with external dorsal and ventral carinae arising from dorsal and ventral acetabular articulations; ventral carinae reaching apex and dorsal carinae before the end (Fig. 22A‒D). Right cercus with proximal tooth pointed; predental margin with two rows of 3+3 round denticles; postdental margin with a row of 16 small round denticles reaching near the hook.

Left cercus toothless, proximal margin with three rows of 4+3+4 denticles: superior and inferior round rows with denticles, intermediate row with tiny round denticles; medial and distal margin with 12 small round denticles ending before the hook. Right cercus with 18, 32, 30 dorsal, lateral, and ventral M; left cercus with 19, 30, 30 dorsal, lateral, and ventral M; both with a few sM and ms, plus campaniform sensilla regularly distributed on internal margins and at the hook (Fig. 22B).

Taxonomic affinities In 1929, Silvestri described a new genus and species, Opisthjapyx seurati Silvestri, 1929, from the central Sahara at the Oued Tezzeït in the south of Algeria. This species is well-defined by its abundant macrosetae (M) along the body, with 14+14 M on the pronotum and 15+15 M on the mesonotum and metanotum. Additionally, it exhibits urosternites with abundant macrosetae and double rows of denticles in both cerci.

Opisthjapyx naledi sp. nov., found in a South African cave, exhibits several differences from O. seurati. Four of these differences can be attributed to cave life: a larger body size (27.5 mm compared to 17 mm in O. seurati), longer antennae (0.35 ratio of body length to antenna length compared to 0.23 in O. seurati), 49 antennomeres (compared to 36 in O. seurati), and a greater number of placoid sensilla on distal antennomeres.

Two other distinguishing features of O. naledi include the number of thoracic macrosetae (M), with 11+10 M on the pronotum and 9+9 M on the mesonotum and metanotum (compared to 14+14 and 15+ 5 in O. seurati), as well as the presence of three rows of denticles instead of two rows as seen in O. seurati. Habitat The single known specimen of Opisthjapyx naledi sp. nov. was found in the Villa Louisa Cave. This cave is located in the Cradle of Humankind, UNESCO World Heritage Site (Gauteng Province, South Africa).

The region is highly diverse in species, as it is associated with the Rocky Highveld Grassland. The rainy period is during the hot summer months, with an annual average of 700 mm. The caves in the area are mainly developed in dolomitic bedrock, associated to the Monte Christo Formation (Malmani Subgroup, Transvaal Supergroup) (Dirks et al. 2015).

Despite extensive search efforts for invertebrates in the cave, only one single specimen was found, thus indicating the rarity of this species. The specimen was found in a deeper, moist, and aphotic area within the cave. The specimen was found under a rock, sheltering in a small chamber, likely dug by itself (Fig. 23D).

After removing the rock, the japygid remained immovable and only left the soil chamber after it was disturbed with a brush tip; it started to run in search of another shelter. However, it did not react to the light, thus not presenting any phototaxy. The Villa Louisa Cave’s external area is highly altered, especially by deforestation.

Furthermore, near the cave’s entrance (approximately 70 meters), there is an asphalt factory posing a pollution threat. The caves’ entrance has small bush patches surrounded by grass (Fig. 23A). Its interior is highly impacted due to the removal of calcite deposits, and the conduits and floor were severely altered in part by walls that were built inside it (Fig. 23B) and tyres that were installed to serve as a staircase in the entrance chamber (Fig. 23C).

The cave still receives local visitors and presents signs of religious use (candles and jars). The risk of contaminants originating from the farms and factories near the cave certainly represents a major concern for this species’ conservation. Furthermore, we need further samplings in the area to determine the actual distribution of this rare species. | Published as part of Sendra, Alberto, Sánchez-García, Alba, Hoch, Hannelore, Jiménez-Valverde, Alberto, Selfa, Jesús, Moutaouakil, Soumia, Preez, Gerhard Du, Millar, Ian & Ferreira, Rodrigo Lopes, 2023, Life in darkness: an overview of cave-adapted japygids (Hexapoda, Diplura), pp. 1-54 in European Journal of Taxonomy 894 (1) on pages 21-29, DOI: 10.5852/ejt.2023.894.2287, zenodo.org/record/8388995