Pholcus crypticolens/opilionoides and phalangioides groups, males, NOR detection A–E, G FISH F Giemsa staining A, B P. opilionoides A diplotene. Three bivalents contain NOR. There is also a signal on the sex chromosome trivalent. Y chromosome overcondensed. Note the scheme of sex chromosome pairing and scheme of the plate (particular elements separated by a dotted line) B two fused sister metaphases II. Note the terminal signal on five biarmed elements belonging to chromosome pairs. Odd number of chromosomes with signal suggests that NOR locus of one chromosome pair is heterozygous for NOR cluster. The X1 chromosome includes NOR at both ends C P. creticus, mitotic metaphase. Two chromosome pairs contain a terminal NOR. Y chromosome overcondensed. On the right side: scheme of the plate (particular chromosomes marked by a line). Inset: metaphase I, sex chromosome trivalent (without signal). Note the scheme of sex chromosome pairing D, E P. alticeps D metaphase I. Two bivalents contain NOR. There is also signal on the sex chromosome trivalent. Y chromosome overcondensed. Note the scheme of sex chromosome pairing E two fused sister metaphases II, Y chromosome overcondensed. NOR bearing elements: one pair of biarmed chromosomes (a terminal NOR), one pair of acrocentric chromosomes (a terminal NOR at long arm), X2 chromosome (a terminal NOR at long arm), X1 chromosome (NOR at both ends). Inset: X1 chromosome (from another plate), note the NOR at both ends F, G P. phalangioides, Madeira, metaphase I. Four bivalents include a NOR. There is also a signal on the sex chromosome trivalent. Note the scheme of sex chromosome trivalent. Abbreviations: a = chromosome of the acrocentric pair bearing NOR, b = bivalent containing NOR, bi = chromosome of a biarmed pair bearing NOR, c = centromere, ch = chromosome bearing NOR, s = sperm nucleus, SCT = sex chromosome trivalent, X1 = X1 chromosome, X2 = X2 chromosome, Y = Y chromosome. Scale bars: 10 μm except for insets (5 μm).