http://www.seaslugforum.net/showall/protatra
http://rfbolland.com/okislugs/protatra.html
http://rfbolland.com/okislugs/prot_ova.html
http://www.ne.jp/asahi/kappa-kuri/miyamoto/OSEHOO/umiushi74.html
http://www.sea-slug.com/species/umiusi019.htm
http://www.umiushi.info/photo_species/photo_splist_eng.php?sopt=0&loc=0000
http://www.h.do-up.com/home/takayan/takapage.htm
http://www.medslugs.de/E/Pac-NW/Protaeolidiella_atra/Selection.htm
http://www.nudipixel.net/species/protaeolidiella_atra/
http://www.umiushi-zukan.com/eng/list_pic.php?ssw=g&kind_id=454