When using the built in file manager you will notice the names psacln and psaserv in addition to your account system username. psacln and psaserv are actually linux groups created by Plesk and which are used for various services and files. For example parent-level directories that should not be shared between sites uses the psaserv group, and files inside of your site will use the psacln group.
These groups cannot be changed or modified by you and are part of the normal Plesk environment.
