^^^^^^^------------------- Sorry. Wasn't paying close attention. The second, lower picture is from the other (left) side. If you take that apart, can you extract the crank spindle through the bottom bracket? If you have the spindle with chainring in hand, you may be able to discover more. Other than that, It looks like the ring with the indents on the chainring side could be a lockring. But you might bugger it up trying to remove it if you don't have the correct tool. Can you confirm that there is no freewheel on the crank?