These are some false scorpions, Pseudoscorpionida. They are not truly parasites, having phoretic association with some invertebrates and vertebrates (do not feed on the host, use it just for distribution). 

These are some false scorpions, Pseudoscorpionida. They are not truly parasites, having phoretic association with some invertebrates and vertebrates (do not feed on the host, use it just for distribution). 

pseudoscorpion, possibly  Chelifer cancroides

Hello,

One thing is certain : identifying a pseudoscorpion to species level based on pictures like this is totally impossible.

Try amplification of CO1 (HCO/LCO) and check on BOLD for genus identification.

Definitely not an ectoparasite, Pseudoscorpions use hosts only for dispersion. As other  people suggested before, it's impossible to identify the species and probably the genus too from a picture; for that you need to check the position and number of trichobothria on the chelicera or on the palpal chela and other similar diagnostic characters under a good microscope.

Thank you all of you.

Francesco could I get some papers on this species

is a pseudosporpion

I agree with all of the predecessors. Vladimir Kaprivin is right, they are not parasites at all, they use the host just to spread to other places.

Try the following site: http://www.museum.wa.gov.au/catalogues/pseudoscorpions

Perhaps contacting with the specialist will hep with the ID. I suggest to provide better pictures and complete locality data.

Try with Mark Harvey at [email protected] and MArk Judson at [email protected]

Good luck!

I have some bibliography about Pseudoscorpions but I'm not a taxonomist of this group. As Camilo suggested , it's better to contact a specialist to have more information. In addition to the names already suggested you can also try to contact Giulio Gardini [email protected].

thank you very much

Pay attention, that pseudoscorpions (they are present on the photo) are not parasites at all.

Pseudoscorpiones are not parasites but they may be predators which attacks the true parasites (e.g. ticks).

In many texts pseudoscorpions are said to be examples of phoresis - i.e. they disperse by temporarily attaching themselves to flying insects, typically bumble bees. As Pavel says they are certainly not ectoparasites. 

Cabal! Foresis! No ectoparásito...

Thank you all of you for your kind consideration and teaching the ideas about pseudoscorpions. I was thinking as ectoparaiste at the moment when it  was attaching to the abdomen of rat. Once again thanks

for identification you will need pictures of the underside, details of the mouthparts, antennae and claws and probably sexual organs; looks like you have male and female but again it could juvenile and adult, as Paulo suggested: find the local expert as it is difficult to validate identity from a picture

Could the rat be phoretic agent?

 Moira Sir could you send me some papers on the pseudoscorpion. Which one is male the bigger or the smaller one

 http://cjai.biologicalsurvey.ca/b_10/b_10.html for Canadian key to pseudoscorpions but it has an explanation of sexing; i believe the one on the left is the female but again hard to tell from a picture, http://www.museum.wa.gov.au/catalogues/pseudoscorpions for world key