Riscus Den Heyer, 2006

Skvarla, Michael J., Fisher, J. Ray & Dowling, Ashley P. G., 2014, A review of Cunaxidae (Acariformes, Trombidiformes): Histories and diagnoses of subfamilies and genera, keys to world species, and some new locality records, ZooKeys 418, pp. 1-103 : 61-62

Riscus Den Heyer, 2006

Historical review.

Gupta and Ghosh (1980) described Cunaxa bambusae , Cunaxa cynodonae Den Heyer (2006) erected Riscus for Riscus thailandensis . Den Heyer (2011) transferred Cunaxa bambusae and Cunaxa cynodonae to Riscus based on the redescriptions by Corpuz-Raros (2008). Den Heyer and Castro (2012) described Riscus austroamericanus .

Diagnosis.

Gnathosoma. Pedipalps 5-segmented, extend beyond the subcapitulum by at least the last segment, and end in a strong claw; apophysis absent. Basifemora and telofemora complemented with simple setae; these two segments fused, although a line remains visible and they can thus be differentiated. Subcapitulum complemented with 6 pairs of setae (hg1-4 and 2 pairs of adoral setae). Setae hg3 and hg4 both near the coxal bases of the pedipalps.

Idiosoma, dorsal. Female dorsal idiosoma has a sclerotized plate that bears 2 pairs of setose sensillae (at and pt) and 2 pairs of simple setae (lps and mps). Idiosomal shield covered by integumental papillae that form a reticulated pattern. Hysterosoma lacks a plate and bears 7 pairs of setae (c1-2, d1-h1). Cupule im present, usually laterad or in the proximity of e1.

Idiosoma, ventral. Coxae ill-defined. Coxae I and II fused; coxae III and IV fused. Coxae I-IV setal formula 3-1-3-1 (including paracoxal seta). Genital plates each bear 4 setae. Anal plates bear 1 pair of setae (ps1). 2 pairs of setae (ps2 and h2) associated with, but do not occur on, the anal plates. Cupule ih present in close proximity to h2. Integument between plates striated and bears 5 pairs of additional setae. Legs. Ambulacral claws on either side of a 4-rayed empodium present.

Key to adult female Riscus

(modified from Den Heyer and Castro 2012)

1	Five pairs of genital setae	Riscus austroamericanus Den Heyer & Castro, 2008
-	Four pairs of genital setae; tibiae IV with 1 T, 4 sts; tibiae II with {1 asl, 1 sts}, 4 sts	2
2 (1)	Pedipalpal genu with 3 sts	3
-	Pedipalpal genu with 4 sts	Riscus bambusae (Gupta & Ghosh 1980)
3 (2)	Pedipalpal tibiotarsus with 1 spls, 3 sts, 1 dorsoterminal solenidion	Riscus thailandensis Den Heyer, 2006
-	Pedipalpal tibiotarsus with 5 sts, 1 dorsoterminal solenidion (original description states 6 sts present; one of these is assumed to be a solenidion here)	Riscus cynodonae (Gupta & Ghosh, 1980)