Tyrannobunus aculeus, BARTEL & DUNLOP, 2023

BARTEL, CHRISTIAN & DUNLOP, JASON A., 2023, First eupnoid harvestmen (Arachnida: Opiliones: Eupnoi) from mid-Cretaceous Kachin amber, with notes on sexual dimorphism in Halitherses grimaldii (Arachnida: Opiliones: Dyspnoi), Palaeoentomology 6 (3), pp. 278-291 : 282

Species Tyrannobunus aculeus sp. nov.

( Figs 1–3 ) urn:lsid:zoobank.org:act:931B8E05-C546-4BC4-9C63-72F95DB46511

Holotype. GPIH05127 , ex coll. Patrick Müller BUB4517.

Paratype. MHNG-ARTO-28161

Etymology. From the Latin word aculeus (spine). Gender masculine.

Diagnosis. As for the genus.

Locality and horizon. Burmese amber, Hukawng Valley, Kachin State, Myanmar; mid-Cretaceous.

Description. Holotype. Body rather small and oval, L 1.28, anterior W 0.91, maximum posterior W 0.90. Dorsal anterior body covered with microgranulation. Dorsal posterior body mostly equivocal, except posterior border which is covered with at least eight large setiferous tubercles. Ocular tubercle relatively large, finely granulated and located at the anterior border, L 0.21, W 0.24. Lateral eye lenses also large, eye lens diameter 0.09. Chelicerae rather small. Cheliceral fingers with multiple equally sized teeth. Cheliceral basal segment L 0.17, cheliceral distal segment L 0.18, cheliceral fingers L 0.14. Pedipalps relatively long and covered with multiple large spines and setiferous tubercles from the trochanter to the tibia. Trochanter with at least three very large ectal spines, femur with four ectal spines (three large and one smaller proximally), patella with two pairs of large spines and an additional mesal apophysis (almost as long as tibia), tibia with three large mesal spines, at least two ectal spines and an apophysis or a large tubercle distally. Pedipalp tarsus mostly unarmed and setose, except one mesal setiferous tubercle/apophysis proximally and up to two smaller ectal spines proximally. Pedipalp claw smooth. Pedipalp length: tr 0.14, fe 0.51, pa 0.20, ti 0.31, ta 0.45, total (tr–ta) 1.61. Legs long (leg II longest) and heavily armed with differently sized spines and setiferous tubercles from the coxa to the tibia. Femur II less armed and thus only covered with a few small spines. Metatarsus and tarsus somewhat setose. Coxa ventrally covered with pairs of sometimes setiferous tubercles. Borders between coxa I–IV sometimes with a row of small bristles. Tarsus I–IV subdivided into tarsomeres, ending in a single smooth and sickle-shaped claw. Tarsal formula: 12; 24; 14; 15. Leg length: Leg I cx 0.38, tr 0.18*, fe 0.76*, pa 0.20, ti 0.41, mt 0.84, ta 1.09, total (cx–ta) 3.86; Leg II cx 0.50*, tr 0.16, fe 3.11, pa 0.37, ti 2.57, mt 2.71, ta 2.80, total (cx–ta) 12.22; Leg III cx 0.45*, tr 0.17*, fe 0.88*, pa 0.23, ti 0.49*, mt 0.86, ta 1.29, total (cx–ta) 4.37; Leg IV cx 0.66*, tr 0.18, fe 1.36, pa 0.27, ti 0.65*, mt 1.63*, ta 1.49, total (cx–ta) 6.24.

Lateral borders of the ventral opisthosoma and borders between sternites with a few finely serrated rows.

Penis elongate and slender, L 1.03 (with stylus). Distal region with drop-shaped glans. Glans without visible ornament. Stylus thin and somewhat tapering distally, L 0.14.

Paratype. Body small and somewhat rounded, L 1.32, anterior W 1.04, maximum posterior W 0.98. Dorsal body mostly equivocal. Posterior body covered with relatively large tubercles. Chelicerae small. Cheliceral basal segment L?, cheliceral distal segment L 0.23, cheliceral fingers L?. Pedipalps relatively long and covered with multiple large spines and setiferous tubercles from the femur to the tibia. Femur with at least three larger mesal spines, patella with a mesal apophysis (almost as long as tibia), tibia with four large mesal spines and at least three ectal spines. Pedipalp tarsus mostly unarmed and setose, with a smaller mesal apophysis proximally. Pedipalp tarsus additionally covered with microgranulation. Pedipalp length: tr?, fe 0.38, pa 0.19, ti 0.25, ta 0.47, total (fe– ta) 1.29. Legs long (leg II longest but incomplete) and heavily armed with differently sized spines and setiferous tubercles from the coxa to the tibia. Metatarsus and tarsus somewhat setose. Coxa ventrally covered with pairs of sometimes setiferous tubercles. Borders between coxa I–IV sometimes with a row of small bristles. Tarsus I –IV subdivided into tarsomeres, ending in a single smooth and sickle-shaped claw. Tarsal formula: 12;?; 13; 12+. Leg length: Leg I cx 0.34, tr 0.13, fe 0.72, pa 0.26, ti 0.32, mt 0.75, ta 0.85, total (cx–ta) 3.86; Leg II cx 0.45, tr 0.13, fe 1.74, pa?, ti?, mt?, ta?; Leg III cx 0.45, tr 0.19, fe 0.60, pa 0.28, ti 0.38, mt 1.17, ta 0.77, total (cx–ta) 4.37; Leg IV cx 0.58, tr 0.17, fe 1.19, pa 0.21, ti 0.43, mt 1.64, ta 0.87, total (cx–ta) 6.24.

Lateral borders of the ventral opisthosoma with a finely serrated row. Ventral opisthosoma, including sternites,almostcompletelycoveredwithmicrogranulation or rows of fine serration. Anal operculum rounded L 0.21, W 0.17.

Remarks. MHNG-ARTO-28161( Fig.3 ) ( Tyrannobunus aculeus sp. nov.) can confidently be recognised as such by the presence of heavily spined legs and pedipalps. The body size and number of leg tarsomeres seems to be almost identical. There are some differences in the number of spines, tubercles and/or apophyses on the pedipalps, and the large setiferous tubercles on the posterior border of the dorsal body, already seen in ventral view in the other specimen, are missing. Particularly, the spination on the pedipalp femur is different to that of GPIH05127, which shows much larger spines. This might be related to sexual dimorphism, as males usually bear a stronger developed armature. For that reason, this second specimen could be the female. On the other hand, the microgranulation on the ventral opisthosoma and on the pedipalp tarsus seem to be stronger developed in this specimen. Unfortunately, this fossil is less well preserved than the holotype and again all dorsal characters cannot be fully resolved. Nevertheless, the barely visible silhouette of the ocular tubercle resembles the condition seen in GPIH05127. Based on the similarities to the specimen described above, this fossil is treated here as the paratype of Tyrannobunus aculeus sp. nov.

Figures

FIGURE 1. Tyrannobunus aculeus gen. et sp. nov., holotype: GPIH05127. A, Camera lucida drawing of the complete specimen in ventral view. B, Close up of the dorsal body and ocularium, eye lenses arrowed. C, Close-up of the ventral body. Abbreviations: ey, eye lens; fe, femur; mt, metatarsus; oc, ocular tubercle; pa, patella; pe, penis; pp, pedipalp; ta, tarsus; legs numbered from I–IV. Scale bars = 1.0 mm (A) and 0.5 mm (B, C).

FIGURE 2. Tyrannobunus aculeus gen. et sp. nov., holotype: GPIH05127. A, Close-up of the ocularium (camera lucida drawing). B, Close-up of the chelicerae and pedipalps in ventral view (pedipalp patella apophysis arrowed). C, Camera lucida drawing of the penis. D, Close-up of the penis in ventral view. Abbreviations: ap, apophysis; bo, body; ch, chelicerae; ey, eye lens; gl, glans; oc, ocularium; pe, penis; pp, pedipalp; st, stylus; tc, truncus; legs numbered from I–IV. Scale bars = 0.5 mm (A, C) and 0.25 mm (B, D).

FIGURE 3. Tyrannobunus aculeus gen. et sp. nov., paratype: MHNG-ARTO-28161. A, Overview of the body in ventral view. B, Close up of the ventral body. C, Close-up of the pedipalps in ventral view. D, Close-up of the ventral opisthosoma, fine serration arrowed. Abbreviations: ao, anal operculum; ap, apophysis; ch, chelicerae; cl, claw; pp, pedipalp; legs numbered from I–IV. Scale bars = 1.0 mm (A), 0.5 mm (B) and 0.25 mm (C, D).