The diploid chromosome complement of
S. nubila is 2n=14 including sex chromosomes of the XY type. This karyotype is very similar to that of
Pericoma modesta but the sex chromosomes in
S. nubila are smaller. Like in
P. modesta they behave as univalents and regularly pass undivided to opposite poles at first meiotic anaphase. Otherwise spermatogenesis is normal. A supernumerary chromosome was found in one specimen among thirty examined.