Sidymella lobata, Machado & Teixeira, 2021

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 : 293

“angularis clade ”

The maximum likelihood analyses performed by Sirvid et al. (2013) for 28S and H3 sequences and combining COI, 28S, H3 and ND1 data are consistent with the morphological evidence presented here in showing some degree of relationship between Si. trapezia + Si. longipes and S. angularis ( Fig. 2 ). Likewise, we obtained good support values for the clade that gathers species from New Zealand ( Si. angularis + Sidymella sp. 2 ). This clade seems to be more related to Stephanopis than to its congeneric species from Australia (e.g. Si. trapezia + Si. longipes ). Despite somatic similarities have been observed and scored for both the “ longipes clade” and the “ angularis clade”, features common to this latter and Stephanopis (stricto sensu), especially regarding the architecture of copulatory structures, seem to outweigh the body features (even the diagnostic shape of the opisthosoma) that taxonomically would place them in Sidymella . This is the main reason why we also justify the transference St. lobata comb. nov., besides aiming for the most stable and parsimonious taxonomic decision. More importantly, we see this as another indicative that the bifid/trapezoidal opisthosoma in Sidymella as currently accepted can be a evolutive convergence that reflects the hunting/cryptic behaviour of distinct groups that are not necessarily closely related in taxonomic and phylogenetic terms. According to Sirvid et al. (2013), the recent establishment of Si. longipes and Si. trapezia in New Zealand suggests a capacity of long-range dispersal over water, contrary to the vicariant hypotheses usually considered to explain the distribution of stephanopines in the Australian region. Although Sirvid et al. (2013) had found molecular evidence supporting separate New Zealand lineages within the Australasian stephanopines, the hypothetical reconstruction discussed here suggests a proximity between Si. angularis , a common species that is widely spread in New Zealand, and Sidymella sp. 2 , recorded along the east coast of Australia ( Fig. 3 ). The node grouping the two species was recovered by all optimality criteria except equal weights ( Fig. 2 ) and showed significant branch supports ( Fig. 3 ). The clade presented one synapomorphy: the presence of dual median spire on the thoracic portion of the prosoma (Char. 24, state 1; see Fig. 15h ), a feature that was mentioned by Bryant (1933) and Sirvid et al. (2013) as a putative character to suggest a new generic assignment to Si. angularis . There is a significant number of undescribed species in Australian collections that present similar characteristics observed in Si. angularis and Sidymella sp. 2 (pers. obs.). An analysis with a broader sampling, molecular data and a biogeographical approach would help to elucidate the phylogenetic relationships and dispersal mechanisms used by these crab spiders along the Australian region.

Figures

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

Fig. 3 Clade supports obtained by relative Bremer index (above the branches) and symmetric resampling analysis (below the branches). A colour scheme is applied to represent the geographical distribution of the clades represented on the working phylogenetic hypothesis

Fig. 15 Characters relative to legs, claws and opisthosoma of specimens sampled in the present analysis: a Epicadus heterogaster, patella I. b Stephanopis pentacantha, patella I. c Isala cambridgei comb. nov., male tibial brushes. d Epicadus caudatus, trichobothrium and duster-shaped setae. e Tmarus elongatus, tarsal claws of the right leg I (mesial view). f Epicadus taczanowskii, tarsal claws of the right leg I (ectal view). g Epicadus heterogaster, tibia I. h Epicadus trituberculatus, opisthosoma