The Highest Chromosome Number and First Chromosome Fluorescent in situ Hybridization in the velvet worms of the family Peripatidae.

The diversity of Onychophora is poorly studied, despite there being nearly 200 described species divided in two families: Peripatidae and Peripatopsidae. Peripatid velvet worms are found mainly in the Neotropical region. The low morphological diversity in Peripatidae is an obstacle to determining its taxonomy, and chromosomal analyses can help clarify this. The aim of this work was to chromosomally analyze one species of Epiperipatus from Mato Grosso do Sul, Brazil. Conventional staining and telomeric fluorescent in situ hybridization (FISH) were performed with the gonads of three males of Epiperipatus sp. The specimens showed 2n♂ = 73, the largest diploid number found in Onychophora to date, with the majority of chromosomes acro/telocentrics and the largest element submetacentric. The FISH marked the telomeric region of all elements and revealed one Interstitial Telomeric Site (ITS) on the proximal region of the long arm large submetacentric chromosome. The absence of male meiosis and female cell division in the analyzed specimens prevented us from determining whether the unpaired large submetacentric is a sex chromosome, which could lead to the description of a rare sex chromosome system (SCS) in Onychophora, or a case of fusion between autosomes. In either case, the presence of ITS is a clear indication of chromosomal fusion.