http://www.pictonb.freeserve.co.uk/nudibranchs/thepen.html
http://www.mermaid1.demon.co.uk/thecacer.jpg
http://www.seaslugforum.net/factsheet.cfm?base=thecpen
http://www.bio.bris.ac.uk/teaching/units/b11000/nudi1.htm
http://rfbolland.com/okislugs/thecpenn.html
http://slugsite.us/bow/wirtz99/plate_5/wirtz_3m.htm
http://www.medslugs.de/E/Atl-E/Thecacera_pennigera/Selection.htm
http://www.ne.jp/asahi/kappa-kuri/miyamoto/OSEHOO/umiushi84.html
http://www.umiushi.info/photo_species/photo_splist_eng.php?sopt=0&loc=0000
http://www.sea-slug.com/species/umiusi336.htm
http://www.h.do-up.com/home/takayan/takapage427.htm
http://www.wttfw.freesurf.fr/biology/biology_liste.php?langue=uk&action=classif#Opistobranchia
http://www.medslugs.de/E/Pac-NW/Thecacera_pennigera/Selection.htm
http://www.medslugs.de/E/Pac-W/Thecacera_pennigera/Selection.htm
http://www.medslugs.de/E/Atl-NE/Thecacera_pennigera/Selection.htm
http://www.habitas.org.uk/marinelife/species.asp?item=W13760
http://www.medslugs.de/E/Med/Thecacera_pennigera/Selection.htm
http://www.scuba-equipment-usa.com/marine/JAN06/Winged_Thecacaera(Thecacera_pennigera).html
http://www.nudipixel.net/species/thecacera_pennigera/
http://www.daveharasti.com/nelsonbay/seaslugs/pagefive.htm
http://hypselodoris.blogspot.pt/2012/02/thecacera-pennigera-montagu-1815.html
http://www.umiushi-zukan.com/eng/list_pic.php?ssw=g&kind_id=176
http://www.dragonmouse.com.au/diving/nudibase.php?action=nudidetail&id=90
http://www.medslugs.de/E/Atl-SE/Thecacera_pennigera/Selection.htm
http://opistobranquis.info/en/guia/nudibranchia/euctenidiacea/doridacea/thecacera-pennigera/
http://www.medslugs.de/E/Pac-SW/Thecacera_pennigera/Selection.htm
http://www.medslugs.de/E/Ind-NW/Thecacera_pennigera/Selection.htm