Foveacorpus, Bartel & Dunlop & Giribet, 2023

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 : 434-435

Genus Foveacorpus gen. nov.

urn:lsid:zoobank.org:act:695BD267-DC04-4076-932D-5D0A81E2CDB5

Type species. Foveacorpus cretaceus gen. et sp. nov.

Etymology. From the Latin words “fovea” (= pit) and “corpus” (= body). Masculine in gender.

Diagnosis. Body oval, small and completely covered with numerous small pits. Rounded ozophores in type 1 position. Chelicerae moderately long and thin. Pedipalps rather small and unmodified. Legs relatively short and robust, with legs I and II directed forwards. Typical spiracles absent. Anal region with a corona analis (sternites 8, 9 and tergite IX fused and forming an unbroken ring around the anal plate) .

Remarks. The holotype of Foveacorpus cretaceus sp. nov. (GPIH05129; Figs. 11–12 ) is interpreted as an adult female due to the open gonostome ( Fig. 11B, D ) and the absence of an adenostyle on tarsus IV. This very small specimen shows an unusual and potentially unique combination of characters. First, the whole body is completely covered with small pits ( Fig. 11 ), a feature which has not been observed in any modern species, and the dorsum shows no sign of segmentation or of a longitudinal opisthosomal sulcus. There are extant stylocellid species, such as Leptopsalis foveolata Clouse & Schwendinger, 2012 , which feature a few much larger and deeper pits on the opisthosoma. It is possible that these small pits in the cuticle of this fossil are an artefact resulting from the fossilization process where, e.g., a substance coats different parts of the specimen, as seen in many Burmese amber fossils. However, the ventral region around the gonostome ( Fig. 12A ) shows no signs of a coating as many small setae are clearly visible and the pits appear to be open. We conclude that most parts of the fossil are originally preserved, and that the pits on the prosoma and opisthosoma were presumably covered by some substance.

Placement of this fossil in the family Stylocellidae can be excluded with some confidence due to the presence of a corona analis in the fossil were sternites 8, 9 and tergite IX are fused ( Fig. 12B ). In stylocellids, all sternites are fused except sternites 8, 9 and tergite IX that surround the anal plate. Margins between the fused tergites and sternites are completely absent in the amber specimen, whereas most modern Cyphophthalmi show at least a slight change in cuticle texture marking these borders. Besides this, there is an unusual setose region between the anterior coxae ( Fig. 12A ). The legs of the fossil are also untypical when compared to most extant Cyphophthalmi . Legs I and II seem to be directed forwards and the right leg III appears to be modified, as it looks more robust than the other legs. The latter is also covered by numerous thick setae, while the left leg III looks thinner, with normally sized setae ( Fig. 11B, D ). This limb condition (except for the modified leg III) is similar to a peculiar modern species from Kenya, Marwe coarctata Shear, 1985 , whose family assignment (like that of the fossil) is still unclear. Additionally, both species possess a corona analis, type 1 ozophores and dorsal areas without any visible sutures between them. On the other hand, Marwe coarctata has a different habitus with an expanded, disc-like posterior portion of the prosoma, it is larger and has stouter chelicerae. In summary, the new fossil has a unique set of characters and cannot be easily placed within any of the extant families.

Figures

FIGURE 11. Foveacorpus cretaceus gen. et sp. nov., female holotype (GPIH05129). A. Whole body, dorsal view. B. Same, ventral view. C. Camera lucida drawing of A. D. Same of B. Abbreviations: ca, corona analis; ch, chelicerae; oz, ozophore; pp, pedipalp; legs numbered from I–IV. Scale bars equal 0.5 mm.

FIGURE 12. Details of Foveacorpus cretaceus gen. et sp. nov., female holotype (GPIH05129). A. Close-up of chelicerae, pedipalps and gonostome (indicated by arrows), ventral view. B. Close-up of opisthosoma, ventral view. Abbreviations: ca, corona analis; ch, chelicerae; go, gonostome; pp, pedipalp; oz, ozophore; legs II, III and IV numbered. Scale bars equal 0.2 mm.