Paraquanothrus, Norton & Franklin, 2018

Norton, Roy A. & Franklin, Elizabeth, 2018, Paraquanothrus n. gen. from freshwater rock pools in the USA, with new diagnoses of Aquanothrus, Aquanothrinae, and Ameronothridae (Acari, Oribatida), Acarologia 58 (3), pp. 557-627 : 599-600

Relationship of Paraquanothrus and Aquanothrus

Paraquanothrus and Aquanothrus appear to represent sister-groups that are respectively distributed in North America and Africa. Paraquanothrus can be distinguished from Aquanothrus by the following synapomorphies. (1) The inconspicuous opening of the bothridium, flush to the surface (vs. the plesiomorphic elevation of the bothridial wall from the surrounding cuticle). (2) The perforation of coxisternal apodemes ap2, ap3 (vs. solid). (3) The absence

(loss) of coronal setae on the ovipositor (vs. presence of normal three pairs). (4) The absence

(loss) of distal cilia on the labrum (vs. their presence). (5) The expression of palp tarsal setae acm and su as normal setae, i.e. their eupathidial nature lost (vs. with eupathidial form). (6)

The proximal dorsal enlargement of the palp tarsus to incorporate insertions of cm, acm and

ω (vs. slight enlargement, with acm maintaining distinct basal tubercle). (7) The unusual structure of trochanters III and IV, with the articulating stalk attached subterminally (vs. typical terminal right-angle bend at proximal end of trochanter). (8) The unusual form of femora III, IV somewhat rectangular in lateral view: proximally broad but abruptly narrowed to articulating stalk, forming vertical face (vs. gradually tapered proximally). (9) The different location of respiratory stigma on femora III, IV (on or near proximal vertical face) compared to that of I, II

(low on paraxial face near mid-length of segment) (vs. location similar on all femora). (10) The regressive loss of solenidion ω2 from tarsus II (vs. its presence). (11) Pretarsal monodactyly

(vs. tridactyly). (12) The presence of lateral, aggenital and posteroventral leathery patches on the gastronotum of juveniles (vs. their absence). (13) The passing of dehiscence line δ above cupule ip in nymphs (vs. below ip). (14) Several regressive setal losses (vs. their presence): (a)

loss of v′ from trochanters I, II; (b) loss of v′ from genua I, II; (c) losses of primiventral setae,

including pv′ from tarsus I, pair (pv) from tarsus II, pv′ from tarsus III, and pv″ from tarsus IV.

Aquanothrus can be distinguished from Paraquanothrus by the following synapomorphies.

(1) Dorsosejugal scissure medially interrupted, i.e. with medial fusion of notogaster and prodorsum (vs. completely separated). (2) Dorso- and pleurophragmata large, conspicuous

(vs. small, inconspicuous). (3) Respiratory stigma on all leg femora nearly dorsal (vs. that of I, II in middle or low position on adaxial face). The coating of epibiotic diatoms or other organic material also seems unique to Aquanothrus . We have seen no diatoms on the cuticle of Paraquanothrus grahami , and those occasionally seen on P. spooneri seem of a normal,

free-living type.

If these relationships are true, several incongruencies are apparent. (1) Most obvious is the presence in P. spooneri of saccules on leg femora and porose areas on trochanters III, IV,

whereas in P. grahami and species of Aquanothrus all femora and trochanters III, IV have tracheae. As invaginated respiratory surfaces, tracheae have been considered apomorphic relative to saccules (Norton and Alberti 1997). (2) Paraquanothrus spooneri develops iteral setae on legs I-III, but they are lost (apomorphic) from P. grahami and known Aquanothrus species. (3) Paraquanothrus spooneri has unusually elongated tectal setae tc (), an apomorphy shared with A. montanus , but not the other (unnamed) Aquanothrus species.