Armadillidium, Brandt, 1833

Hyžný, M & Dávid, A, 2017, A remarkably well-preserved terrestrial isopod (Peracarida: Isopoda: Armadillidiidae) from the upper Oligocene of Hungary, with remarks on the oniscidean taphonomy, Palaeontologia Electronica 20 (1), pp. 1-11 : 4

Genus ARMADILLIDIUM Brandt, 1833

Type species. Armadillo vulgaris Latreille, 1804 , by original designation.

Diagnosis. See Sars (1899, p. 188) and Richardson (1905, p. 665); see also Schmalfuss (2013, p. 13).

Remarks. Armadillidiids constitute a well-founded monophyletic group ( Schmidt, 2008) that comprises about 300 species. The most speciose genus is Armadillidium Brandt, 1833 , with nearly 200 described forms ( Schmalfuss, 2003), including A. vulgare ( Latreille, 1804) , the “most extensively investigated species of terrestrial isopods,” as noted by Schmalfuss (2003, p. 2). According to Schmalfuss (2013), the genus is defined by: 1) ability to roll up into a closed ball, which may have a lemon-like shape; 2) lungs with multiple spiracles in 1 st and 2 nd pleopod-exopodite; 3) uropod-exopodite flattened and truncated, filling the space between epimeron of pleonite 5 and telson; 4) frontal part of head with a triangular shield (which seems to be a modified supra-antennal line) reaching the level of the upper head surface or surpassing this level; 5) lateral parts of inter-ocular line present. Unfortunately, the Hungarian specimen does not possess a head, which precludes a confident generic assignment. However, we argue that based on various clues discussed below it is reasonable to assign the specimen to Armadillidium .

The pereonite-epimeron I does not have a notch (schisma), which is characteristic for many genera, i.e., Alloschizidium Verhoeff, 1919 ; Ballodillium Vandel, 1961 ; Eluma Budde-Lund, 1885 ; Paraschizidium Verhoeff, 1918 ; and Schizidium Verhoeff, 1901 . Thus, the assignment of the Hungarian specimen to these genera can be excluded. Also, based on the smooth cuticular surface, the assignment to genera with tuberculated representatives, i.e., Cyphodillidium Verhoeff, 1939 ; Echinarmadillidium Verhoeff, 1901 ; Paxodillidium Schmalfuss, 1985 ; and Platanosphaera Strouhal, 1956 , can be excluded. Cristarmadillidium Arcangeli, 1935 ; Eleoniscus Racovitza, 1907 ; Trichodillidium Schmalfuss, 1989 ; Troglarmadillidium Verhoeff, 1900 ; and Typhlarmadillidium Verhoeff, 1900 , are known only from a few species, and their distribution is rather limited. For instance, representatives of Trichodillidium are so far known only from Greece, including Crete and adjacent islands ( Schmalfuss, 1989, 2003), whereas monotypic Eleoniscus is restricted to southeastern Spain ( Racovitza, 1907; Schmalfuss, 2003). A vast majority of all species of the family Armadillidiidae belong to the genus Armadillidium ( Schmidt, 2003) ; therefore it is the most parsimonious course of action to interpret the Hungarian specimen as a representative of this genus. In addition, the autochtonous European distribution of Armadillidium ( Schmalfuss, 2000, 2013) strengthens the argument in favour of attributing the Hungarian specimen to that genus.