http://www.pictonb.freeserve.co.uk/nudibranchs/polqua.html
http://www.asterisk.no/~emil/nudibranchia/polycera_quadrilineata.htm
http://www.ntnu.no/~vmzotbak/nudibranchia/polyceridae/polycera_quadrilineata.htm
http://www.nudibranch.org/Scottish%20Nudibranchs/polycera-quadrilineata.html
http://slugsite.us/bow/wirtz98/p_5_3.htm
http://slugsite.us/bow/wirtz98/p_5_4.htm
http://www.medslugs.de/E/Atl-NE/Polycera_quadrilineata/Selection.htm
http://www.seaslugforum.net/showall/polyquad
http://slugsite.us/bow/wirtz99/plate_4/wirtz_3i.htm
http://www.medslugs.de/E/Atl-E/Polycera_quadrilineata/Selection.htm
http://www.medslugs.de/E/Med/Polycera_quadrilineata/Selection.htm
http://www.wttfw.freesurf.fr/biology/biology_liste.php?langue=uk&action=classif#Opistobranchia
http://www.ugr.es/~lstocino/pagina_nueva_22.htm
http://www.nembro.info/uk_polycera_quadrilineata.html
http://www.habitas.org.uk/marinelife/species.asp?item=W13630
http://www.seawater.no/fauna/Blotdyr/quadrilineata.htm
http://www.guiamarina.com/gallery/v/Baltic+Sea/03+Animals/05+Mollusca/Opisthobranchia/Polycera+quadrilineata/
http://www.nudipixel.net/species/polycera_quadrilineata/
http://hypselodoris.blogspot.pt/2008/07/polycera-quadrilineata-muller-1776.html
http://opistobranquis.info/en/guia/nudibranchia/euctenidiacea/doridacea/polycera-quadrilineata/