Freshwater maricola exception - Pentacoelum sp. , most likely Pentacoelum kazukolinda from jar culture which was left as is for some time.
Sadly no idea about origin, too many 'inoculums' ended in that certain jar so I count those as captive case which randomly appeared in our tropical lab tanks and got chance to thrive when was moved into separate jar. Species determinaion is in WIP stage. Juvenile is depicted at oblique illumination photo, adults on darkfield.