227 2007. The Journal of Arachnology 35:227–237 CYTOGENETICS IN THREE SPECIES OF POLYBETES SIMON 1897 FROM ARGENTINA (ARANEAE, SPARASSIDAE) I. KARYOTYPE AND CHROMOSOME BANDING PATTERN Sergio Gustavo Rodrı ´guez-Gil: Laboratorio de Citogene ´tica y Evolucio ´n, Departamento de Ecologı ´a, Gene ´tica y Evolucio ´n, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires. Intendente Gu ¨iraldes y Costanera Norte, C1428EHA. Ciudad Auto ´noma de Buenos Aires, Argentina. E-mail: rodrigil@bg. fcen.uba.ar Marı ´a Susana Merani: Centro de Investigaciones en Reproduccio ´n, Facultad de Medicina, Universidad de Buenos Aires, Paraguay 2155, C1121ABG, Ciudad Auto ´noma de Buenos Aires, Argentina. Cristina Luisa Scioscia: Divisio ´n Aracnologı ´a, Museo Argentino de Ciencias Naturales ‘‘Bernardino Rivadavia’’, Av. A ´ ngel Gallardo 470, C1405DJR, Ciudad Auto ´noma de Buenos Aires, Argentina. Liliana Marı ´a Mola: Laboratorio de Citogene ´tica y Evolucio ´n, Departamento de Ecologı ´a, Gene ´tica y Evolucio ´n, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires. Intendente Gu ¨iraldes y Costanera Norte, C1428EHA. Ciudad Auto ´noma de Buenos Aires, Argentina. ABSTRACT. Species of Polybetes are known exclusively from South America. Currently there are 13 described species, 9 occurring in Argentina. Cytogenetic studies in spiders are scarce; the cytogenetics of only about 1% of nearly 39,500 described species are known. Within the Sparassidae, 38 species out of 1,009 ( 4%) have been cytogenetically analyzed; the most frequent chromosome number is 2n = 43/46 (male/female), n = 20 + X 1 X 2 X 3 , present in almost half of the species studied. Female diploid chromosome number is only known for four species: Heteropoda venatoria (Linnaeus 1767) (2n = 44); Pediana regina (L. Koch 1875), Isopeda sp. and Olios sp. (2n = 46). Within the genus Polybetes, only P. pythagoricus (Holmberg 1875) had been previuosly cytogenetically analyzed. In the present work, the karyotype, het- erochromatin content and distribution, and silver stained nucleolus-organizer regions of P. pythagoricus, P. rapidus (Keyserling 1880) and P. punctulatus Mello-Leita ˜o 1944 are described and compared. In P. pythagoricus the identification of the chromosome pairs by means of G-banding is also performed. Females of the three species show a chromosome complement of 44 telocentric chromosomes, with a similar karyotype. Males of P. pythagoricus show 42 telocentric chromosomes, the two sex chromosomes being the largest and of different size. In the three species, two pairs of telomeric NORs and small pericentrom- eric positive C-bands in all chromosomes were detected. This C-banding pattern seems to be characteristic of spiders. Comparative analysis of chromosome complements in Sparassidae indicates that 2n = 42/44 (X 1 X 2 0/X 1 X 1 X 2 X 2 ) (male/female) may represent the ancestral karyotype for Polybetes. Keywords: Chromosome number, telocentric chromosomes, heterochromatin, nucleolus-organizing regions Species of Polybetes are known exclusively from South America. To date there are thirteen described species, nine of them occurring in Argentina (Platnick 2006): P. germaini Simon 1897, P. martius (Nicolet 1849), P. obnuptus Simon 1896, P. pallidus Mello-Leita ˜o 1941, P. punctulatus Mello-Leita ˜o 1944, P. pytha- goricus (Holmberg 1875), P. quadrifoveatus (Ja ¨rvi 1914), P. rapidus (Keyserling 1880), and P. trifoveatus (Ja ¨rvi 1914). In nature, they are found under the bark of trees (e.g., P. py- thagoricus is common under the bark of Eu- caliptus), in the branches of trees (P. rapidus), and others are found in grasses such as Cor- taderia spp. (P. punctulatus). Polybetes pytha- goricus and P. rapidus are also common in