Mesopsalis, 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 : 425

Genus Mesopsalis gen. nov.

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Type species. Mesopsalis oblongus sp. nov.

Etymology. Named after its presence in the Mesozoic and its similarities to the modern genus Leptopsalis . Masculine in gender.

Diagnosis. Relatively large and oval body with a markedly subtriangular anterior margin. Elongated ozophores in the type 2 position. Eyes present. Chelicerae rather small and sparsely granular. Legs relatively short and granular. Leg tarsi undivided, bearing a single smooth claw. Coxa I free, coxae II–III fused. Opisthosomal sternal sulci mostly straight and parallel. Anal plate unmodified.

Remarks. The holotype of Mesopsalis oblongus sp. nov. (MB.A.4456; Fig. 2 ) is very likely an adult female due to the absence of an adenostyle on tarsus IV, its relatively large size and the open gonostome. The habitus of this specimen with its elongated ozophores ( Fig. 2A–B ) appears to be similar to that of the holotype of Palaeosiro burmanicum . However, the new fossil is nearly three times larger and has an eye lens in front of each ozophore, which is lacking in P. burmanicum . The families Ogoveidae and Pettalidae can be excluded as this fossil does not show any of the typical characters like a longitudinal median furrow in the scutum completum, a large opisthosomal ventral apophysis, upwards facing ozophores and a strongly modified anal region. The free coxa I, fused coxae II–III ( Fig. 2D ) and the conical anterior end of the carapace, in combination with an unmodified anal plate, indicate affinities to the family Stylocellidae . The conical anterior margin of the body ( Fig. 2B ) of the fossil resembles that of the modern species Leptopsalis ramblae Giribet, 2002 . The presence of eyes, slightly curved ventral opisthosomal sulci and the reduced cheliceral ornamentation is also shared between the fossil and specimens of the modern genus Leptopsalis Thorell, 1882 . However, long and relatively thin conical ozophores cannot be observed in any of the extant Leptopsalis species. Based on this unique combination of characters, the fossil is placed in a new genus.

Figures

FIGURE 2. Mesopsalis oblongus gen. et sp. nov., female holotype (MB.A.4456).A. Camera lucida drawing of whole specimen, dorsal view. B. Micro-CT scan of whole specimen, dorsal view. C. Same, lateral view. D. Same, ventral view. Abbreviations: ap, anal plate; ch, chelicerae; ey, eye lens; fe, femur; mt, metatarsus; oz, ozophore; pa, patella; pp, pedipalp; ta, tarsus; ti, tibia; tr, trochanter; legs numbered from I–IV. Scale bars equal 1 mm (A) and 0.5 mm (B–D).