http://www.seaslugforum.net/showall/callbell
http://www.nudipixel.net/species/calliopaea_bellula/
http://sacoglossa.lifedesks.org/pages/34148
http://opistobranquis.info/en/guia/sacoglossa/calliopaea-bellula/
http://www.medslugs.de/E/Med/Calliopaea_bellula/Selection.htm