Parahistricostoma, Mitov & Perkovsky & Dunlop, 2021

Mitov, Plamen G., Perkovsky, Evgeny E. & Dunlop, Jason A., 2021, Harvestmen (Arachnida: Opiliones) in Eocene Rovno amber (Ukraine), Zootaxa 4984 (1), pp. 43-72 : 59-61

Genus Parahistricostoma gen. n.

Diagnosis. Small, dark fossil nemastomatids (body length range 1.25–1.52, body width ca. 1.0) with ovoid to quadrangular body, dorsally with fine granulation, only anterior corners of scutum magnum with more prominent granules, and with four pairs of slender, pillar-like spines, each slightly bulbous at the top, standing perpendicular to the body surface. In males, apophyses resembling an ‘ice-cream scoop’ (or in dorso/dorso-lateral outline, boxing gloves) present on first cheliceral articles; apophysis approx. low, from 0.11 to ca. 0.2 mm. Pedipalps and legs elongate and slender. Pedipalps without apophyses (spurs/thorns/denticles). Palpal tarsus relatively short, in lateral view machete-like – distally rounded and slightly widened; in ventral view – like a baseball bat. Palpal Ta/Ti between 0.44 and 0.55 mm. Microsculpture elements of the leg femurs include loose-textured denticles and granules.

Type species. Nemastoma tuberculatum C. L. Koch & Berendt, 1854 , by original designation.

Etymology. From the Greek ‘para’ (beside, near) and the modern harvestman genus Histricostoma which this material closely resembles. Gender neuter.

Remarks. The extinct genus Parahistricostoma is morphologically closest to the recent genus Histricostoma Kratochvíl , which can be found today from the Alps through to the Balkans, Turkey and the Caucasus, and includes eight species ( Kratochvíl 1958; Staręga 1976b; Martens 1978, 2006; Snegovaya & Marusik 2012; Schönhofer 2013; Iorio & Delfoss 2015). The traditional assignment of Koch and Berendt’s (1854) amber species Nemastoma tuberculatum to the genus Histricostoma was initially based on the presence of false articulations on the leg femora (see Staręga, 2002: 602), and later largely based on its dorsal ornament ( Dunlop 2006; Dunlop & Mitov 2009). As in Histricostoma , four pairs of slender, pillar-like spines, each slightly bulbous at the top (“Stabdorne” sensu Martens 1978) are observed. The distal end of the pedipalp femur in both the fossils and living Histricostoma is similar, and the leg trochanters are spinulate.

However, the question remains do these features alone justify placing the fossil in the modern genus? We could identify at least four subtle differences between the Histricostoma -like fossils and modern Histricostoma species. First, the form of the cheliceral apophysis in the fossils differs from that seen in recent species. Second, there is no evidence for a medial spur (thorn/denticle) on the distal end of the male palpal patella, as is seen in all modern Histricostoma . Third, the legs and pedipalps of the fossils are somewhat longer and more slender than the appendages observed in living species. Finally, the microsculptural elements of the leg femora are also different compared to those in the type species of Histricostoma ( H. drenskii ), as well to those of H. creticum and H. dentipalpe . We feel that this character combination does merit a separate genus, diagnosed as above. Furthermore, lacking any data on the structure of the penis in this fossil species, we cannot resolve its generic relationships through comparing its genital morphology with that of extant species.