This is an entire tapeworm. What you normally see in faeces or stuck around the dog?s bottom are individual segments of tapeworms.
In reality, adult tapeworms consist of a head (with suckers to attach to the intestinal wall), a neck and then continuously produced segments, which contain eggs.
These are passed out in the faeces and then dry out to release the eggs inside.
Your particular tapeworm looks to be Dipylidium Caninum, which affects dogs, cats and foxes and can grow to be up to 20in long.
The life cycle is interesting.
The liberated eggs are eaten by flea larvae and then develop, inside the flea, into an immature form.
When the flea (the intermediate host) is eaten by a dog, cat or fox (the definitive host) the tapeworm develops into an adult and the cycle begins again.
It is important, therefore that you not only worm your dog but also treat it for fleas!
Oh and don?t go sucking the end of that pen!