Cytological and karyological observations on two endemic giant pill-millipedes Arthrosphaera (Pocock 1895) (Diplopoda: Sphaerotheriida) of the Western Ghats of India

Cytological features and karyomorphology of two endemic giant pill-millipedes (Arthrosphaera fumosa and A. magna) of the Western Ghats were studied based on the meiotic cell divisions using Giemsa staining technique. Different meiotic stages of spermatogonial cell divisions were compared and karyotypes were constructed from the metaphase stages. The diploid chromosome number, 2n = 30, in A. fumosa as well as A. magna with XY sex determination system was seen. Most of the meiotic chromosome behaviors were similar between the millipede species. All meiotic chromosomes in A. fumosa belonged to acrocentric type, while in A. magna 27 were acrocentrics, two (3rd and 10th) were sub-metacentrics and one (5th) was metacentric. The relative lengths of autosomes in A. fumosa and A. magna were 21.9-109.3 and 38.8-90.6, respectively. The X chromosome was longer than the Y chromosome in both millipedes. The relative lengths of the X chromosomes of A. fumosa and A. magna were 130.1 and 103.6, while for the Y chromosome they were 113.6 and 92.6, respectively. Based on this study and earlier cytological and karyological studies on Arthrosphaera, the diploid chromosome number has been predicted to be higher than 30. Further assessment is needed of identified and unidentified species distributed in the Western Ghats of India and other geographic locations to follow the chromosomal evolutionary pattern.