What are “malacomorphs”? Well, “malakos” in Greek means literally “soft”, but it’s also by analogy how we scientifically call mollusks, including snails: malacology, for example, is the study of mollusks. So “malacomorphs” are snail-creatures.
For some reason that even most specialists don’t know, many manuscripts have in their corners little illustrations of snails and other animals. In some cases, the snails are crossbred with other animals or even humans. There is even a manuscript with an illustration of people living in snail houses.
Why snails? There are some hypotheses about their possible symbolism, but no one know for sure. Violent rabbits are also popular, which might have influenced Terry Jones in creating that famous scene in “Monty Python and the Holy Grail”.