Juniper's ERX Routing Protocols Configuration Guide has a page explaining IPv6 packet headers. It contains this misleading diagram:
Let's fix it.
The optional 'options' field is included in the IPv4 figure but not the IPv6 figure. It should be in both or neither. Probably neither -- most internet traffic has no options fields.
The ipv6 figure just plain cheats on the size of its address fields. They are not to scale with the rest of the diagram.
Shown with correct scale:
In Juniper's figure, the ipv6 header is 27% bigger than the ipv4 header. Actually, it is 100% bigger -- twice the size: 40 bytes vs 20 bytes. Why would Juniper confuse or misconstrue such a basic property of ipv6?