Compared with araneomorph spiders, relatively few mygalomorph spiders have evolved an obligate existence in subterranean habitats. The trapdoor spider genus Troglodiplura Main, 1969 and its sole named species T. lowryi Main, 1969 is endemic to caves on the Nullarbor Plain of southern Australia, and is one of the world’s most troglomorphic mygalomorph spiders. However, its systematic position has proved to be difficult to ascertain, largely due to a lack of preserved adults, with all museum specimens represented only by cuticular fragments, degraded specimens or preserved juveniles. The systematic placement of Troglodiplura has changed since it was first described as a member of the Dipluridae, with later attribution to Nemesiidae and then back to Dipluridae. The most recent hypothesis specifically allied Troglodiplura with the Neotropical subfamily Diplurinae, and therefore was assumed to have no close living relatives in Australia. We obtained mitochondrial sequence data from one specimen of Troglodiplura to test these two competing hypotheses, and found that Troglodiplura is a member of the family Anamidae (which was recently separated from the Nemesiidae). We also reassess the morphology of the cuticular fragments of specimens from several different caves, and hypothesise that along with T. lowryi there are four new troglobitic species, here named T. beirutpakbarai Harvey & Rix, T. challeni Harvey & Rix, T. harrisi Harvey & Rix, and T. samankunani Harvey & Rix, each of which is restricted to a single cave system and therefore severely threatened by changing environmental conditions within the caves. The first descriptions and illustrations of the female spermathecae of Troglodiplura are provided. The family Anamidae is further divided into two subfamilies, with the Anaminae Simon containing Aname L. Koch, 1873, Hesperonatalius Castalanelli, Huey, Hillyer & Harvey, 2017, Kwonkan Main, 1983, Swolnpes Main & Framenau, 2009 and Troglodiplura, and the Teylinae Main including Chenistonia Hogg, 1901, Namea Raven, 1984, Proshermacha Simon, 1909, Teyl Main, 1975 and Teyloides Main, 1985.

Southern Australian waters feature remarkably diverse assemblages of the sea spider family Callipallenidae Hilton, 1942. The most speciose of the three Australian-endemic genera currently recognised has been known as Meridionale Staples, 2014, but is here reinstated under the name Pallenella Schimkewitsch, 1909 based on its type species Pallenella laevis (Hoek, 1881). This genus includes several brightly coloured forms that occur in high abundance on arborescent bryozoans. However, considerable similarity of congeners and scarcity of diagnostic characters continue to render species delineation in this genus challenging. Using an integrative taxonomic approach, we combine detailed morphological investigation with analysis of two genetic markers (mitochondrial cytochrome c oxidase subunit I, and nuclear rDNA including internal transcribed spacers 1 and 2) to explore the extraordinary species richness of the genus Pallenella in south-east Tasmania. In agreement with our morphology-based segregation of different species and morphotypes, we recovered well-supported corresponding clades in the genetic analyses. Strong mito-nuclear concordance in the two markers supports the inference of sustained reproductive isolation between the sympatrically occurring forms. Based on these findings, we distinguish a total of 13 Tasmanian congeners, representing the most diverse assemblage of sympatric species in the same microhabitat reported for a single pycnogonid genus. Within this assemblage, we (1) record the type species P. laevis for the first time after almost 150 years, (2) delineate the two Tasmanian morphotypes of the provisional ‘variabilis’ complex, and (3) describe two species new to science (P. karenae, sp. nov., P. baroni, sp. nov.). Despite considerable genetic divergences between most congeners, only few and often subtle characters are found to be suitable for morphology-based delineation. Notably, colouration of living specimens is suggested to be informative in some cases. For morphology-based species identification of preserved specimens, a key relying on combinations of characters rather than single diagnostic features is proposed.

Sexually dimorphic traits are widespread in animals, and include sex-specific weapons, ornamentation and, although less noticed, glands and associated structures. In arachnids, certain lineages of the order Opiliones exhibit diverse forms of dimorphism in the armature and length of appendages (common in Laniatores), as well as in the presence of sexually dimorphic glands (mostly investigated in Cyphophthalmi), positing harvestmen as promising models to study sexual dimorphism. Whereas the evolution and ecological significance of armature have been the focus of recent attention, sexually dimorphic glands remain understudied in groups other than Cyphophthalmi, despite being widespread in Opiliones. We therefore selected the amphi-Pacific family Zalmoxidae as an ideal taxon to investigate the evolutionary dynamics of this trait. We first describe four new species of Palaeotropical Zalmoxis, including a species with sexually dimorphic glands, and describe the morphology of zalmoxid species with sexually dimorphic glands using scanning electron microscopy. Using a previously assembled six-locus dataset supplemented with new terminals, and applying stochastic character mapping, we infer that sexually dimorphic glands evolved once in the Neotropics and at least four times in the Palaeotropic zalmoxids, revealing the evolutionary lability of this trait.

The spider genus Nemoscolus Simon, 1895 (Araneidae) has been neglected taxonomically despite the unique retreat that several species construct in their horizontal orb-webs, composed of pebbles and other detritus. The distribution of Nemoscolus is poorly known and the genus includes species from Africa and Europe. Nemoscolus is placed in Simon’s Cycloseae species group along with Cyclosa Menge, 1866, Acusilas Simon, 1895, Arachnura Vinson, 1863, Witica O. Pickard-Cambridge, 1895, among others. Here we describe a new species from Queensland, Australia, N. sandersi, sp. nov., drastically expanding the distribution range of the genus. We use nucleotide sequence data to phylogenetically place Nemoscolus using model-based inference methods within Araneidae and to explore its affinities to Simon’s Cycloseae. The data support propinquity of Nemoscolus with Acusilas and Arachnura but not with Cyclosa. Our analyses suggest that Cycloseae is not a clade, with Cyclosa, Acusilas, Witica and Nemoscolus not sharing a recent common ancestor. This use of an integrated granular retreat represents at least the second independent evolution of such a structure within Araneidae. These results improve our understanding of both phylogeny and retreat evolution in araneid spiders.