Sidymella trapezia (L. Koch, 1874)

Machado, Miguel & Teixeira, Renato Augusto, 2021, Phylogenetic relationships in Stephanopinae: systematics of Stephanopis and Sidymella based on morphological characters (Araneae: Thomisidae), Organisms Diversity & Evolution (New York, N. Y.) 21 (2), pp. 281-313 : 294-295

“trapezia clade ”

The relationship between Si. trapezia and the species that Sirvid et al. (2013) call “near corticalis ” showed to be poorly supported by maximum likelihood analyses of COI sequence data. The uncertainty regarding the species identity and low sampling of Australian taxa in that study were possibly the main reasons of such result. Here, morphological traits did not recover Si. trapezia as close related to St. corticalis , let alone the placement of Si. longipes in Stephanopis . Both these Sidymella species were grouped in the same clade with Si. bicuspidata by three homoplasies related to leg characteristics ( Fig. 7 ). However, the topology of the group was inconsistent and weakly supported, sometimes with S. trapezia behaving as a wildcard and occasionally Si. bicuspidata + Si. longipes emerging separately. Every so often, parsimony with implied weights recovered only S. trapezia as a sister group to the “ cambridgei clade” and occasionally in a clade with Si. bicuspidata + Si. longipes as a sister to the “ cambridgei clade”, being this latter in a dichotomy with Stephanopis . As observed for the “ angularis clade” and “ hirsuta clade”, the “ trapezia clade” also shares with the “ altifrons clade” and the “ cambridgei clade” the presence of CP close to the RTA of the male palp. Such structure seems to be constant in these groups of Australian stephanopines and might contribute to their weakly resolved relationship in the face of their remarkable somatic disparities.

The “ trapezia clade” is formed by taxa that clearly do not fit with the recently updated diagnosis of Sidymella and the taxonomic background presented by Machado et al. (2019a) was corroborated by the emergence of the Neotropical species far apart from those hitherto called “Australian Sidymella ”. Additionally, the analyses of molecular data presented by Sirvid et al. (2013) show Si. trapezia emerging independently from other taxa or, when grouped in a more inclusive clade, presenting low values of branch support. Therefore, we believe that although significantly heterogeneous and lacking good nodal stability, the “ trapezia clade” must be proposed as a new genus in a future taxonomic work. Only then, the most parsimonious decision will be taken, avoiding the maintenance of a paraphyletic status for Sidymella , erection of a monospecific genus to accommodate only Si. trapezia or the proposition of the three species as incertae sedis.

The species Si. rubrosignata behaved unpredictably, presenting even weaker support and being more unstable than the “ trapezia clade”. Alternative resolutions represented this species emerging within the “ Epicadus group” due to the presence of characters such as the disk-shaped tegulum on the male palp (Char. 95, state 0) and the median longitudinal band (Char. 12, state 1) with a guanine white spot on the thoracic portion (Char. 16, state 1), or independently (as shown in the discussed tree), but always as sister to the remaining taxa of the ingroup ( Fig. 2 ). Considering all analyses and morphological evidence presented here, once again, justifying the description of a stephanopine species in Sidymella based merely on the presence of a pair of lateral projections on the opisthosoma has proven to be insufficiently grounded and inaccurate. None of the diagnostic features regarding the male palp architecture or copulatory duct disposal of species of Sidymella is observed in Si. rubrosignata . The independent emergence of this taxon is recovered by 10 homoplastic characters and supports Simon’ s (1895) insights considering it as a group apart from Stephanopis as well ( Fig. 7 ). Thus, we believe that Si. rubrosignata deserves a new generic assignment.

Figures

Fig. 7 Section of the working phylogenetic hypothesis detailing the character transformations and relationships between the “angularis clade” (orange), Sidymella rubrosginata (red), “trapezia clade” (blue)

Fig. 2 Hypothetical reconstruction of the relationships of Stephanopis and Sidymella based on the strict consensus of the most congruent tree (K = 17.89) obtained after implied weighted analysis. Nodal stability is represented by the “Navajo rugs” along the branches (analysis recovering