Arcochthonius, 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 : 366-367

Arcochthonius n. gen.

Zoobank: DE56E962-A279-49E4-AC76-FC4DC12FC679

Type species: Arcochthonius roynortoni n. sp.

Diagnosis — Adults unique among known Brachychthoniidae (Thor, 1934) by following combination of character states: prodorsum and notogaster with sclerotized plates and ridges, rostral apex and lateral edge of prodorsum with teeth, anterior edges of medial and posterior notogastral sclerites with transverse thickenings, spanned by arched clamp-like ridges, notogastral seta d 2 situated close to d 1, far from lateral notogaster margin, seta c 3 inserting on distinct embossed plate on anterior notogastral sclerite NA, suprapleural sclerite SpE distinct, lateral to anterior transverse scissure, other suprapleural sclerites absent, suprapleural incision distinct, anterior and posterior pleural sclerites separated, epimeres IV with 4 pairs of setae, genital sclerites with 7 pairs of setae, aggenital sclerites present, adanal sclerites posteriorly fused, adanal seta ad 2 hypertrophic, femur IV with 2 setae, genua III and IV each with 2 setae, tarsal setal formulas I–IV 18–14–13–11.

Description of adult — Enarthronote oribatid mite, placed in the family Brachychthoniidae . Body in lateral view arched, prodorsal and notogastral sclerites thickened and sculptured with plates and ridges. Prodorsum strongly elevated, anterior edge bent ventrad. Prodorsal surface with transverse and longitudinal ridges. Rostral apex with three teeth. Lateral edge of prodorsum serrated sawtooth-like, with 3–4 larger teeth posterior to serration. Five pairs of prodorsal setae (rostral, lamellar, interlamellar, anterior exobothridial, bothridial seta). Exobothridial hump protruding, posterior exobothridial seta represented by small pore. Bothridial seta small, with numerous small bristles. Notogaster elevated, divided in three separated sclerites by two broad transverse scissures. Anterior edges of notogastral sclerites NM and NP with distinct transverse thickenings, spanned by arched clamp-like ridges. All sclerites with larger and smaller plate-like ridges. Marginal suture on notogastral sclerite

NA absent. 16 pairs of notogastral setae, c 1, c 2, c 3, d 1, d 2, d 3, e 1, e 2, f 1, and h 1 inserting on tubercles on distinct plates, f 2, h 2, h 3, p 1 –p 3 inserting on small tubercles on NP. Pygidium strongly arched caudally. Pygidial and pleural sclerites ventrally surrounded by disjugal suture. Pygidial sclerite with deep suprapleural incision, separating posterior pleural sclerite laterally about halfway from pygidium. Suprapleural sclerite SpE distinct, SpC partially fused with notogastral sclerite NA, visible part indistinctly protruding caudad. Sclerites SpD and SpF absent. Anterior and posterior pleural sclerites separated by distinct furrow. Lyrifissures ia

– ips in pleural region. Subcapitulum anarthric, with 4 pairs of setae and 1 pair adoral setae. Rutellum atelobasic. Chelicera of chelate type, with one seta. Palp setal formula (trochanter to tarsus, solenidion in parentheses): 0–2–1–3–10(1), (u) fused and forked eupathidium on palptarsus, solenidion on palptarsus originating near base of seta cm. Epimeres I and II fused medially, separated from III and IV by sejugal furrow. Epimeres III and IV separated medially. Epimeral setal formula 3–1–3–4. Genital sclerites with 7 pairs of setae, aggenital sclerites undivided with 1 pair of setae, peranal sclerite narrow with 1 seta each, anal sclerites with 2 pairs of setae, adanal sclerites fused posteriorly, with 3 pairs of setae, seta ad 2 hypertrophic.

All legs monodactylous, claws smooth. Setal formulas of legs (trochanter to tarsus, famulus included, solenidia in parentheses): leg I 0–3–3(2)–5(1)– 18(3), leg II 0–4–3(1)–4(1)–14(1),

leg III 2–3–2(1)–3(1)–13, leg IV 1–2–2(1)–4(1)–11. All setae setiform, smooth.

Etymology — The genus name has two meanings: The prefix Arco- “ “ derives from the arched (latin arcus) clamp-like ridges on the anterior edges of notogaster sclerites. It is also a homage to the municipality of Arco/Trentino (Northern Italy), my second home, where I prepared part of this work. It is compounded with -chthonius “ ”, a common generic root for Pseudoscorpions and enarthronote genera (from ancient Greek χθόΝΙΟΣ, meaning “underworld”

or “subterranean”).