Figure S1. Male sets of diplurids (A) and paratropidids (B). A, Ischnothele caudata, karyotype, silver staining (mitotic metaphase). Three pairs (nos 1, 2, and XY) contain a subterminal NOR. B, Paratropis sp. (Mexico), haploid set without X chromosomes (metaphase II). Note monoarmed chromosomes (nos 17, 19, 24–30, 32, 33, 35, 37–40, 42–46, and 48–53). Two chromosomes are submetacentric/subtelocentric (nos 41 and 47). Scale bars: 10 μm.

Figure S2.Linothele megatheloides (Dipluridae): prophase I of male; arrow, X chromosome(s); open arrow, SCP. A, transition to diplotene. Note a SCB composed by X chromosomes on the nuclear periphery and a positively heteropycnotic SCB formed by SCP; B, diakinesis. The central part of the plate contains X chromosomes and SCP, which is the largest bivalent of the set. Scale bars: 10 μm.

Figure S3. Male set of Ischnocolus jickelii (Theraphosidae, Ischnocolinae): metaphase II. Karyotype consists of metacentrics, except for six submetacentric pairs (nos 11, 20, 24, 32, 33, and 38). The sex chromosomes show a slightly delayed condensation and chromatid separation. Scale bar: 10 μm.

Figure S4. Male karyotypes of the theraphosid subfamily Theraphosinae, based on metaphases II. A, Holothele cf. longipes, chromosomes are biarmed, except for two monoarmed pairs (nos 2 and 35). B, Grammostola rosea, chromosomes are metacentric, except for two submetacentric (nos 12 and 19) and one subtelocentric (no. 32) pairs as well as submetacentric X2 chromosome Scale bars: 10 μm.

Figure S5. Male karyotype of Iberesia machadoi (Nemesiidae): mitotic metaphase. Scale bar: 10 μm.

Figure S6. Male sets of ctenizids (A) and idiopids (B), based on mitotic metaphases. A, Ummidia sp. (monoarmed pairs: nos 16 and 19). B, Idiops syriacus (submetacentric/subtelocentric pairs: nos 23–25). Chromosomes are arranged into pairs tentatively because the sex chromosome system is unknown. The odd element is the putative X chromosome. Open arrowheads – large terminal secondary constrictions. Scale bars: 10 μm.

Figure S7. Male of Cyrtocarenum cunicularium: late spermatogonial metaphase. Note association of SCP chromosomes (open arrows). Scale bar: 10 μm.

Table S1. Basic data concerning collection (localities, sex, and instar of specimens used) and evaluation (*families studied for the first time, 1relative chromosome lengths were not determined, 2relative lengths of X chromosomes were not determined). aCA, California; Co., county; MX, Mexico; NR, nature reserve; RSA, Republic of South Africa. Unless otherwise indicated, deposited in collection of J. Král (BD, B. Drolshagen; NMP, National Museum, Prague; RJR, R.J. Raven). bf, female; fn, female nymph; m, male; mn, male nymph; sf, subadult female; sm, subadult male.

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