As usual some jagged edges etc. should be invisible in the book, since it's going to be reproduced pretty small.
The idea was later used by James White in one of his Sector General books, the second collection of Ambulance Ship stories I think.
That's almost the last creature, apart from some living crystals from Pluto, basically nanobots with an appetite for metal, carbon, etc. Next I start on the tech side of things, space travel, etc. which will hopefully go a bit faster.
Incidentally, does "Load Up On Guns (Friends Optional)" sound good as a title for the section on weapons?