Phylogenetic relationships of Kimberleytrachia
Our phylogeny (Figs 2-3) supports the basal position of a clade including K. aequum Köhler, 2011, K. nelsonensis n. sp. and K. serrata n. sp. These species exhibit a rather flat shell (H/D<0.52) with periostracal projections on the entire surface (Köhler, 2011b: fig. 218; Figs 4C-D, 6D-F, 7A-C in Appendix). Although most Kimberleytrachia species exhibit a moderately elevated shell (H/D>0.52), a flat shell is characteristic for Torresitrachia and all other closely related genera (except Succochlea n. gen. and Rhagada Albers, 1860 [in Martens and Albers, 1860]). Therefore, a flat shell probably represents an ancestral character state in Kimberleytrachia. The penial anatomy of K. aequum and K. nelsonensis n. sp. is assumed to be largely plesiomorphic in possessing all typical features of the genus, such as a well-developed pad-like structure and regular, well-spaced and smooth epiphallic and penial longitudinal pilasters and transverse lamellae (Köhler, 2011b: fig. 220). The inner penial wall sculpture of most other species appears to be characterised by increased complexity (sinuous lamellae as in K. jacksonensis n. sp., presence of pustulation as in K. deflecta, fusion of elements such as in K. somniator Köhler, 2011) or by the loss of features (K. alphacentauri Köhler, 2011).
Kimberleytrachia and Succochlea n. gen. have strikingly similar genital anatomies including a corresponding layout of penis and epiphallus. Despite the remarkable complexity, our phylogeny suggests that these anatomical configurations likely are the result of parallel evolution.