Not all of the creatures could be fitted into the film ... the polar portion of the expedition was skipped entirely ... and the "plot" was changed from a manned exploration to an entirely mechanized remote one, but these were changes that worked (and viewers who hadn't read the book wouldn't know the difference anyway). Definitely something to watch again and again and again. :-)
P.S. And if you haven't read the book, seek it out ... 'tis a marvel!