The family of Velvet spiders (Eresidae) consists of nine genera and 95 species (list). The majority of species lives under a surface in slopes, deserts or semi-deserts of Old World. The species richest regions are Mediterrain (mainly Northern Africa and Midle-East) and Southern Africa.
Most of the european species belongs to genus Eresus. Probably due the spectacular coloration of Eresus males they attracted naturalists since old times. Neverthat, in Velvet spiders is still a lot of species waiting to be described, and even new genus has been described recently (Miller et al. 2012). As obvious in many groups of spiders or invertebrates there is still a lot species to discover.
There are many complications in eresid systematic. First is the access to material. Mainly species from Mediterrain are very rare and it is sometimes extremely hard to find them. Due the hidden life style they are not frequently found in pitfall traps (only adult males catched when searcing for females). Secondly, taxonomical characters, differing certain species are very gentle in genus Eresus. That is why is still a lot of undescribed species even in "well studied countries" of Europe.
Relatively good situation in generas Stegodyphus, Seothyra and Dorceus whose been revisted. Absolutelly chaos is in africain species of Dresserus and Gandanameno and unfortunatelly also in a majority of Eresus. Lets hope that future works brings a more light into the eresid diversity.