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 : 290-291

“altifrons clade ”

In the taxonomic work provided by Machado et al. (2019b), the authors suggested the possible existence of three distinct groups of species in the genus ( “ cambridgei group”, “ altifrons group” and “ lata group”). This latter was not independently recovered by non-ambiguous synapomorphies as alphataxonomy insights previously suggested. Instead, all its component species emerged in a single and weakly supported clade with species assigned to the “ altifrons group” (sensu Machado et al. (2019b)). Moreover, a dichotomy between this major clade with Stephanopis barbipes Keyserling, 1890 + St. lobata comb. nov. was recovered based on three homoplastic features. Despite its considerable heterogeneity, hereinafter we call this group as the “ altifrons clade”.

A m on g the s pe ci es th at co m p r i s e S t e ph a no pi s, Stephanopis erinacea Karsch, 1878 stands out as the only insular taxon, occurring far from the Australian territory, being recorded in the Fiji Islands. The restricted distribution and specific selective pressures possibly suffered by this species may have contributed to the evolution of a highly apomorphic organism that, although retaining some important similarities with its congeners, had developed distinct somatic features and “ hirsuta clade” (purple). Filled squares represent synapomorphies and those in white are homoplastic characters. Character states: red (0); black (1); green (2); blue (3)

that are not observed in any other Stephanopis species. Besides that, the male of St. erinacea is unknown; thus, a significant portion of the matrix related to male genitalic features was not scored for this taxon, possibly contributing to the poor resolution and the instability of the clade. The unpredictable behaviour of this terminal taxon in the EW analyses led us to perform another method for topology test. As a result, the removal of this wild card through pruning in equal weights analysis resulted in gaining six additional nodes in the outgroup resolution while the topology of the “ altifrons clade” remained stable (Appendix 3). One way or another, the group presented in the main hypothetical reconstruction was supported by homoplasies ( Fig. 8 ): the absence of dorsolateral projections on the opisthosoma and absence of both macrosetae on the ocular quadrangle (char. 43, state 0; see Fig. 9g ) and clypeus margin (char. 19, state 0; see Fig. 9g ). All males of the “ lata group” (sensu Machado et al. (2019b)) (e.g. Stephanopis lata O. Pickard-Cambridge, 1869 , Stephanopis armata L. Koch, 1874 , Stephanopis monulfi Chrysanthus, 1964 , Stephanopis bicornis L. Koch, 1874 , Stephanopis angulata Rainbow, 1899 , Stephanopis corticalis L. Koch, 1876 , Stephanopis fissifrons Rainbow, 1920 and Stephanopis squalida Machado, 2019 ) present a diagnostic structure on the dorsal portion of their cymbium: a group of arrow-shaped setae arranged close together that looks similar to a small brush (char. 117, state 1; see Fig. 20h ). However, this structure was interpreted as ambiguous in our analyses because the male of St. erinacea is unknown, and palpal characters are missing for this terminal taxon. Thus, this feature was not represented along the tree branches. According to Dr. Martín Ramírez (pers. comm), this setae cluster probably has a chemosensory function. High-magnification SEM images of these structures were not taken, so further investigations should be carried out to verify this assumption. Males of the “ lata group” (sensu Machado et al. (2019b) also have a truncated branch on the ventral portion of the RTA (char. 106, state 0; see Fig. 14a ) while neither females nor males in this group have the remarkable cephalic prominence observed in the “ altifrons group” (sensu Machado et al. (2019b)) ( Fig. 11a ). This latter emerged as a derivate group with its putative synapomorphies being the high cephalic portion (char. 22, state 2; see Fig. 10d ) bearing a pair of lateral tubercles (char. 20, state 1; see Fig. 9g ) ( Fig. 5 ). Comparative studies with morphometric and ecological approaches must be encouraged to test if the flattened habitus of species of the “ altifrons group” (sensu Machado et al. (2019b)) could be related to a specific niche specialization (hunting on trunks and under tree bark), as Dias and Brescovit (2003) suggested for Pachistopelma rufonigrum Pocock, 1901 , a theraphosid spider that lives in bromeliads, or Morebilus plagusius Platnick, 2002 , a dorsoventrally flattened trochanteriid adapted to live in crevices and under sun-exposed rocks ( Goldsbrough et al. 2004). According to Goldsbrough et al. (2004), the development rate of M. plagusius specimens is increased due to the high temperatures of the surfaces where they live under.

Recovered by five homoplastic characters and presenting significant nodal stability and branch supports, the clade ( St. barbipes + Si. lobata ) is clearly the most controversial clade in Stephanopis ( Figs. 1 and 3 ). A series of leg characteristics set these two species apart from the rest of the main clade. Their distinct trichobothria disposition (char. 46, state 0; see Fig. 12f ), morphology of tarsal claws (char. 69, state 1; see Fig. 13e ) and density of the setae tuft, as well as the length proportion between their metatarsal macrosetae (char. 71, state 1; see Fig. 14a ), might explain the divergence from other species of the genus. However, genitalic features such as the presence of pars pendulum on male palp (char. 115, state 1; see Fig. 20a, g ) and membranous chamber-like copulatory ducts in female genitalia (char. 88, state 1; see Machado et al. (2019b), Fig. 37d) pull them together as the sister clade of the “ lata + altifrons ” group. The recovery of Si. lobata as a sister species to St. barbipes was strongly supported, and for that reason as well as the presence of diagnostic genitalic characters, the most parsimonious decision was to keep this latter species in Stephanopis and propose the transference of Si. lobata as it clearly does not fit in Sidymella instead of erecting a new genus to accommodate both. However, there are substantial somatic differences with other Stephanopis species and we highlight that the placement of St. barbipes and St. lobata comb. nov. (formally proposed hereinafter) is highly questionable and deserves future investigation.

Figures

Fig. 8 Characters relative to dorsal habitus and prosoma of specimens sampled in the present analysis: a Stephanopis lata, frontal view. b Sidymella excavata, frontal view. c Stephanopis pentacanha, carapace. d Epicadinus trispinosus, carapace. e Tmarus polyandrus, carapace. f Isala arenata comb. nov., dorsal habitus. g Epicadus granulatus, sternum. h Borboropactus nyerere, sternum

Fig. 9 Characters relative to carapace and sternum of specimens sampled in the present analysis: a Sidymella bicuspidata, sternum. b Epicadus caudatus, sternum. c Onocolus intermedius, sternum. d Geraesta hirta (white arrows indicate pointed setae; black arrows indicate filamentous setae). e Sidymella trapezia, sternum. f Phrynarachne ceylonica, sternum. g Stephanopis macrostyla, prosoma. h Isala cambridgei comb. nov., prosoma

Fig. 20 Characters relative to the male genitalia of specimens sampled in the present analysis: a Stephanopis fissifrons, grooved RTA. b Sidymella lucida, nodose RTA. c Isala palliolata comb. nov., smooth RTA. d Epicadus taczanowskii, canoe-shaped RTAbvr. e Sidymella hirsuta, spoon-shaped RTAvbr. f Coenypha ditissima comb. nov., left palp. g Sidymella furcillata, left palp. h Isala spiralis comb. nov., left palp

Fig. 14 Characters relative to legs of specimens sampled in the present analysis: a Sidymella kolpogaster (arrows indicate femoral setae). b Sidymella trapezia (arrow indicates femoral setae). c Stephanopis monulfi, leg I. d Stephanopis lata, leg I. e Epicadus heterogaster, femoral setiferous tubercles. f Epicadus caudatus, femoral setiferous tubercles. g Geraesta hirta, leg I. h Stephanopis pentacantha, leg I

Fig. 11 Characters relative to prosoma and mouth parts of specimens sampled in the present analysis: a Stephanopis monulfi, frontal view. b Sidymella sp. 2, frontal view. c Stephanopis quinquetuberculata, lateral view. d Stephanopis pentacantha, e Epicadus taczanowskii, chelicer- ae (detail of papules). f Stephanopoides simoni, chelicer- ae. g Phrynarachne ceylonica, chelicerae. h Epicadus trituberculatus, chelicerae

Fig. 10 Characters relative to prosoma of specimens sampled in the present analysis: a Epicadus caudatus, frontal view. b Epicadus heterogaster, carapace. c Epicadus taczanowskii, frontal view. d Sidymella bicuspidata. e Tmarus elongatus, lateral view. f Epicadus heterogaster, lateral view. g Stephanopis nana, frontal view (black arrows indicate lateral cephalic tubercles; white arrows indicate the not projected lateral margin of the clypeus). h Epicadus rubripes, frontal view (arrows indicate the lateral margins of the clypeus projected laterally)

Fig. 5 Character transformations and detail of the dichotomy between the Isala and Paratobias gen. rev. based on the topology of the most congruent tree (K = 17.89). Filled squares represent synapomorphies

Fig. 1 Topologic comparison between consensuses trees obtained under equal weighting parsimony (EW) and Bayesian inference (BI)

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. 12 Characters relative to carapace and mouth parts of specimens sampled in the present analysis: a Borboropactus cinerascens, labium and endites. b Sidymella kolpogaster, labium and endites. c Tmarus elongatus, frontal view. d Stephanopis altifrons, lateral view. e Isala rufiventris comb. nov., frontal view (arrows indicate cheliceral macrosetae). f Borboropactus cinerascens, frontal view. g Stephanopis barbipes, frontal view. h Stephanopis. bicornis, frontal view

Fig. 13 Characters relative to carapace and legs of specimens sampled in the present analysis: a Stephanopis pentacantha, proso- ma (detail of the procurve poste- rior eye row). b Paratobias championi sp. rev. (detail of the recurve posterior eye row). c Stephanopis fissifrons, prosoma (detail of the straight posterior eye row). d Stephanopis barbipes, prosoma (arrows indicate MOQ macrosetae). e Borporopactus cinerascens, prosoma (canoe- shaped tapetum). f Tmarus elongatus, tibiae I (trichobothria linearly distributed). g Stephanopis pentacantha, tibiae I (clustered trichobothria). h Coenypha edwardsi, leg I (arrows indicate mesial and ectal apophy- sis on femur)