Arcochthonius roynortoni, Schatz, 2021

Schatz, Heinrich, 2021, A new species of Brachychthoniidae (Acari: Oribatida) from the Eastern Central Alps (Austria, Tyrol), with the proposal of a new genus, Acarologia 61 (2), pp. 365-379 : 375-377

Arcochthonius roynortoni n. sp. shares several morphological character states with known

Synchthonius species : body surface strongly sclerotized and arched in lateral view, rostral apex anteriorly with large teeth, lateral edge of rostrum serrated and with large teeth, position of notogastral seta d 2 close to d 1, prosomatic suprapleurite absent, suprapleural sclerite SpE present, sclerite SpC partially fused with NA, other suprapleural sclerites absent, suprapleural incision deep, aggenital sclerite present, adanal seta ad 2 hypertrophic, setal formula on legs.

Arcochthonius differs from the Synchthonius species in the following: pleural sclerites separated in A. roynortoni n. sp. (vs. fused in Synchthonius , see remark #5), seven pairs of genital setae in A. roynortoni n. sp. (vs. six pairs in Synchthonius , see remark #6), large exobothridial hump in A. roynortoni n. sp. (vs. small in Synchthonius ), notogastral seta c 3 on distinct embossed sculpturing in A. roynortoni n. sp. (vs. directly on integument of notogastral sclerite NA in Synchthonius , see remark #4),

The genus Synchthonius Hammen, 1952 includes two described species, S. crenulatus

(Jacot, 1938) and S. elegans Forsslund, 1956 . Moritz (1976b: p. 243) proposed Synchthonius boschmai Hammen, 1952 as a synonym of S. crenulatus (Jacot, 1938) . Subías (2017, unpub-

lished electronic update of his 2004 checklist) placed Liochthonius lentus Chinone, 1974 to

Synchthonius without any comment, a suggestion I reject. This species has some faint irregular spots, but lacks the character states of known Synchthonius species. The figure of the ventral side of this species ( Chinone 1974, fig. 71) depicts different numbers of setae (6/7) on the genital sclerites (see also remark #6).

—setae d 2 close to d 1, 2 —suprapleural sclerite SpC partially integrated in anterior notogastral sclerite NA, weakly protruding, 3 — SpC to a large extent integrated in NA, 4 —bipartite in some species,?—no data available.

Many characters of Arcochthonius are shared with other Brachychthoniidae genera (Table

2). In addition to Synchthonius , species of Poecilochthonius Balogh, 1943 and Verachthonius

Moritz, 1976 show most similarities with Arcochthonius n. gen.: Poecilochthonius : prodorsal and notogastral surface ornamented, lateral rostral teeth present, prosomatic suprapleurite absent, suprapleural sclerite SpE present, pleural sclerites separated, aggenital sclerite present;

Verachthonius : prosomatic suprapleurite absent, d 2 close to d 1, suprapleural sclerite SpE present, pleural sclerites separated, p 2 posterior to p 1, adanal sclerites fused caudally.

The new species differs from the Poecilochthonius and Verachthonius species in the following: ornamentation of prodorsum and notogaster (vs. smooth in Verachthonius , different ornamentation pattern in Poecilochthonius ), rostral apex with three larger teeth (vs. serrations without teeth in Poecilochthonius , smooth and without teeth in Verachthonius ), lateral rostral teeth present (vs. absent in Verachthonius ), seta d 2 close to d 1 (vs. d 2 near notogastral margin in Poecilochthonius ), suprapleural sclerite SpC fused with NA (vs. distinct with seta c 3 in

Poecilochthonius , fused with NA with distinct lateral lobe, seta c 3 on unsclerotized integument in Verachthonius ), seta p 2 posterior to p 1 (vs. p 2 laterocaudal to p 1 in Poecilochthonius ),

suprapleural incision deep and distinct (vs. short in Poecilochthonius and Verachthonius ),

aggenital sclerite present (vs. absent in Verachthonius ), adanal sclerites fused caudally (vs. separated in Poecilochthonius ), adanal seta ad 2 hypertrophic (vs. ad 2 not hypertrophic, setiform in

Verachthonius , ad 2 and ad 3 hypertrophic in Poecilochthonius ).

The morphological differences of Arcochthonius roynortoni n. sp. to species of these and other Brachychthoniidae genera justify the erection of a separate genus.