Stylocellidae, Hansen & Sorensen, 1904

Bartel, Christian, Dunlop, Jason A. & Giribet, Gonzalo, 2023, An unexpected diversity of Cyphophthalmi (Arachnida: Opiliones) in Upper Cretaceous Burmese amber, Zootaxa 5296 (3), pp. 421-445 : 433

Stylocellidae gen. sp. 4

Fig. 10

Material. Specimen BUB1542, ex coll. Patrick Müller; Myanmar, Hukawng Valley; Burmese amber, Upper Cretaceous (Lower Cenomanian).

Description. Body oval, with a narrowly rounded anterior margin; total L 2.98, maximum prosomal W behind ozophores 1.49, maximum opisthosomal W 1.53. Conical ozophores in type 2 position. L of ozophores 0.23, W at base 0.28, distance between base of ozophores 1.16. Chelicerae long ( Fig. 10A–B ) and granular on basal and median segments; small additional setae on basal segment and setiferous tubercles on median segment; cheliceral fingers each with eleven uniform teeth; basal segment L 0.93*, median segment L 0.71, finger L 0.29. Pedipalps long, tarsus with few sensory setae and with a small claw on its tip; pedipalp length: tr 0.32*, fe 0.70, pa 0.23, ti 0.32, ta 0.34, total 1.91. Legs long and robust, furnished with numerous setae on tarsi and metatarsi; trochanter of leg I and II somewhat granular; tarsus IV bearing a somewhat fringed adenostyle in distal third ( Fig. 10C ); leg tarsi not subdivided, bearing a single smooth claw; leg lengths: I tr 0.44*, fe 1.04*, pa 0.32, ti?, mt?, ta?; II tr 0.36, fe 0.97, pa 0.42, ti 0.56, mt 0.19, ta 0.61, total 3.11; III tr 0.46, fe 1.12, pa 0.35, ti?, mt?, ta?; IV tr 0.36, fe 0.85, pa 0.34, ti 0.51, mt 0.29*, ta 0.68*, total 3.03. Gonostome circular, surrounded with small tubercles, W 0.32, L 0.24. Spiracles C-shaped (consisting of small denticles), maximum W 0.11 ( Fig. 10D ). Anal plate rounded and with a potential longitudinal carina, W 0.39, L 0.22.

Remarks. Specimen BUB1542 ( Fig. 10 ) is interpreted as a mature male due to the presence of an adenostyle at the base of tarsus IV and due to its heavy sclerotization. The family Pettalidae can be excluded as the fossil lacks upwards-facing ozophores and a dual dentition on the chelicerae. A large apophysis on the second opisthosomal sternite and a thorn-like adenostyle situated near the middle of the tarsus are also absent in the fossil. Both are typical characters of the family Ogoveidae . This leaves the modern Holarctic Sironidae and the Southeast-Asian Stylocellidae as the only possible placements. The somewhat fringed adenostyle in the distal third of tarsus IV ( Fig. 10C ) indicates stylocellid affinities, especially in combination with the longitudinal carina on the anal plate, a granular second cheliceral segment and C-shaped spiracles ( Fig. 10D ). However, as the reconstruction of many characters was not possible even with the help of micro-CT, we prefer to describe this specimen without naming it as a new species. Nevertheless, this fossil can be easily distinguished from all other cyphophthalmid fossils on the basis of its unique adenostyle on tarsus IV. New material may allow the naming of a new species in the future.

Figures

FIGURE 10. Stylocellidae gen. sp. 4 (male specimen BUB1542). A. Close up of anterior part of body, dorsal view. B. Whole body, ventral view. C. Close up of tarsus IV with adenostyle, ventral view. D. Micro-CT image of right spiracle in ventral view. Abbreviations: ad, adenostyle; ch, chelicerae; cl, claw of tarsus IV; pp, pedipalp; sp, spiracle; legs numbered from I–IV. Scale bars equal 0.5 mm (A), 1 mm (B), 0.2 mm (C) and 0.1 mm (D).