Las angulas are baby eels.  They look like worms.  They are a traditional food in the area of Bilbao where they are prepared by tossing them in olive oil with slices of hot chilli pepper and garlic.  This method of cooking them is called las angulas a la bilbaína.  They are traditionally served in an earthenware dish - una cazuela de barro.

Las angulas are one of the most expensive foods in Spain!  For that reason, there is a cheap, fake alternative made from fish paste.  The paste is formed into little worm shapes to look like real baby eels.  The fake version is called las gulas.   So, be careful and check if you are buying angulas or gulas because there is a big difference in the price!