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 : 428-430

Stylocellidae gen. sp. 1

Figs. 5–6

Material. Specimen BUB601, ex coll. Patrick Müller; Myanmar, Hukawng Valley; Burmese amber, Upper Cretaceous (Lower Cenomanian).

Description. Body oval and tuberculate-microgranular across most of its surface; total L 2.33, maximum prosomal W behind ozophores 1.24, maximum opisthosomal W 1.32. Prosoma completely granular due to small and rounded tubercles, with conical ozophores of types 1 or 2 (no lateral view available) ( Fig. 5A, C ). Anterior part of prosoma and ozophores additionally furnished with small setae. L of ozophores 0.22, W at base 0.25, distance between base of ozophores 0.82. Eight opisthosomal tergites clearly delimited dorsally and uniquely separated by a smooth median groove. Tergites increasingly covered with setae posteriorly. Chelicerae relatively small, covered with small tubercles; cheliceral fingers relatively long; dentition equivocal; basal segment L 0.35, median segment L 0.51, distal segment L 0.23*. Pedipalps sparsely covered sensory setae on tibia and tarsus; tarsus with small claw on its tip; length: tr 0.21, fe 0.40, pa 0.19, ti 0.16, ta 0.17, total 1.13. Legs short and robust, bearing numerous setae on most segments; some leg segments like coxae, femur IV and tarsus IV additionally granular; coxae partly visible in dorsal view; all tarsi entire, not subdivided, with a single smooth and sickle-shaped claw; tarsus IV without adenostyle; leg lengths: I tr 0.21*, fe 0.57*, pa 0.29*, ti 0.36*, mt 0.12*, ta 0.32*, total 1.87; II tr 0.23, fe 0.52, pa 0.29, ti 0.30, mt 0.16, ta 0.46*, total 1.96; III tr 0.26, fe 0.45, pa 0.20, ti 0.28, mt 0.15, ta 0.38, total 1.72; IV tr 0.18, fe 0.46, pa 0.27, ti 0.36*, mt 0.14*, ta 0.28*, total 1.69. Opisthosomal sternites granular and furnished with setae; sternites 2–3 fused to a subtriangular plate. Sternites 4–8 free, their widths: 4, 1.03; 5, 0.96; 6, 0.78; 7, 0.63; 8, 0.45. Gonostome closed, subhexagonal and covered with tubercles of different sizes, W 0.30, L 0.35. Spiracles in the form of an open circle consisting of small denticles and surrounded by similar-sized tubercles, situated on an isolated sclerite behind coxae IV, maximum W 0.05. Anal plate with a longitudinal median carina ( Fig. 6B ).

Remarks. Specimen BUB601 ( Figs. 5–6 ) is a juvenile. The closed gonostome and spiracles located on separate sclerites ( Fig. 6A ) clearly indicate this status. The gender of this specimen is unclear as the typical male adenostyle on tarsus IV first appears after the final moult in most species and no other somatic features allow the sex of juvenile cyphophthalmids to be identified. Due to the shape of the spiracles, which could be either interpreted as an open circle or as C-shaped, we assume that the affinities of this fossil lie with the Stylocellidae or Pettalidae . However, pettalids have much smaller, rounder and more upwards facing ozophores in comparison with the enlarged lateral ozophores observed in the fossil ( Fig. 5A, C ). The ornamented second cheliceral segment ( Fig. 5B, D ) further supports stylocellid affinities. Therefore, we place this specimen in the Stylocellidae , as it would be inappropriate to formally describe a new species based on a juvenile.

Figures

FIGURE 5. Stylocellidae gen. sp. 1 (juvenile specimen BUB601).A.Whole body, dorsal view.B. Same, ventral view. C. Camera lucida drawing of A. D. Same of B. Abbreviations: ch, chelicerae; mt, metatarsus; oz, ozophore; pa, patella; pp, pedipalp; ta, tarsus; ti, tibia; legs numbered from I–IV. Scale bars equal 1 mm.

FIGURE 6. Details of Stylocellidae gen. sp. 1 (juvenile specimen BUB601).A. Close-up of left spiracle, ventral view. B. Closeup of posterior end of opisthosoma, ventral view. Abbreviations: ap, anal plate; cx, coxa IV; go, closed gonostome; sp, spiracle; tr, trochanter; legs III and IV numbered. Scale bars equal 0.2 mm.