Stylocellidae Hansen & Sorensen 1904
Creators: name: Bartel, Christian
name: Dunlop, Jason A.
name: Giribet, Gonzalo
Publisher: name: Zenodo
Year: 2023
Subjects: Biodiversity
Taxonomy
Animalia
Arthropoda
Arachnida
Opiliones
Stylocellidae

description: Stylocellidae gen. sp. 2
Figs. 7–8
Material. Specimen BUB1517, ex coll. Patrick Müller; Myanmar, Hukawng Valley; Burmese amber, Upper Cretaceous (Lower Cenomanian).
Description. Body oval and somewhat very widely subtriangular in profile at anterior end; total L 1.76, maximum prosomal W behind ozophores 1.11, maximum opisthosomal W 1.09. Prosoma almost completely tuberculate-microgranular, especially near outer edges (Fig. 7A, C). Conical ozophores with tubercles and in type 2 position. L of ozophores 0.21, W at base 0.17*, distance between base of ozophores 0.65. Eye lens present anterior to left ozophore. Six opisthosomal tergites visible, each delimited and sparsely granular near left and right edges. Borders delimiting tergites smooth. Chelicerae moderately long, somewhat protruding and completely granular; each cheliceral finger with nine small uniform teeth; basal segment L 0.32, median segment L 0.26, distal segment L 0.22. Pedipalps relatively small and granular, except for tarsus furnished with sensory setae; tarsus with small claw at its tip; pedipalp length: tr 0.14, fe 0.27*, pa 0.21, ti 0.25, ta 0.17, total 1.04. Legs relatively short, robust and strongly granular, especially leg I and II featuring additional setiferous tubercles; coxae not fused; leg tarsi entire, not subdivided, bearing a single smooth claw and numerous setae; tarsus IV without adenostyle; leg lengths: I tr 0.24, fe 0.57, pa 0.24, ti 0.33, mt 0.14, ta 0.44*, total 1.96; II tr 0.21, fe 0.51, pa 0.25, ti 0.33, mt 0.13, ta 0.39, total 1.82; III tr 0.19, fe 0.40, pa 0.21, ti 0.33, mt 0.14, ta 0.32, total 1.59; IV tr 0.22, fe 0.55, pa 0.21, ti 0.21, mt 0.14, ta 0.43, total 1.76.
Ventral side of opisthosoma covered with small tubercles and setae. Opisthosomal sulci parallel to each other. Sternites 2–3 fused to a subtrapezoidal plate; sternites 4–9 getting increasingly concentrated towards anal plate. Gonostome closed, subhexagonal, covered with numerous small and two larger tubercles proximally, W 0.33, L 0.32. Spiracles C-shaped (consisting of small denticles) and surrounded by smaller tubercles, located on isolated sclerites behind coxae IV, maximum W 0.08. Anal plate rounded, with few small tubercles, W 0.20, L 0.15 (Fig. 7B, D).
Remarks. Specimen BUB1517 (Figs. 7–8) is again a juvenile of uncertain gender judging from the closed gonostome and spiracles situated on separate sclerites (Figs. 7B, D, 8B). Therefore most diagnostic characters are not fully developed. Nevertheless, granular tegument, C-shaped spiracles, type 2 ozophores, uniform teeth on cheliceral fingers and an ornamented second cheliceral segment (Fig. 8A) suggest placement in the Stylocellidae. Within Stylocellidae two extant genera feature extensive sculpturing on the second cheliceral segment, similar to that in the fossil: Miopsalis Thorell, 1890 and Stylocellus Westwood, 1874. These can be easily distinguished by the form of the ventral opisthosomal sulci. Stylocellus features sinoidal ventral opisthosomal sulci and Miopsalis features straight ventral opisthosomal sulci (Clouse 2012). The latter can also be observed in specimen BUB 1517. However, the fossil also shows a strong concentration of opisthosomal sternites (Fig. 7B, D) around the anal plate, a character not known from modern genera. This could either be a juvenile character not present in modern species, or it could be related to a deformation of the opisthosoma as a result of its preservation in amber. For that reason we prefer a cautious approach and leave this specimen unnamed.
description: Published as part of Bartel, Christian, Dunlop, Jason A. & Giribet, Gonzalo, 2023, An unexpected diversity of Cyphophthalmi (Arachnida: Opiliones) in Upper Cretaceous Burmese amber, pp. 421-445 in Zootaxa 5296 (3) on pages 430-432, DOI: 10.11646/zootaxa.5296.3.6, http://zenodo.org/record/7984131