Original: Most of the 1,400 or so species are marine , with a few living in fresh water and a small number of terrestrial forms ; they are found in all marine habits , and throughout the world 's oceans .
Simplified: Nemerteans range in size from 5mm ( 0.2 in ) to over 30m ( 100ft ) long in the case of the European Lineus longissimus , with most species being 20cm ( 8in ) or less .