The process whose specific outcome is the progression of the chlamydospore over time, from its formation to the mature structure. A chlamydospores is a mitotic (asexual) one-celled spore, produced primarily for survival, not dispersal, originating endogenously and singly within part of a pre-existing cell and possessing an inner secondary and often thickened cell wall. An example of this is found in Candida albicans.