http://www.seaslugforum.net/factsheet.cfm?base=hydaphys
http://rfbolland.com/okislugs/hydaphys.html
http://www.conchology.uunethost.be/GENERAL/Cyberconchology/SuperConch/Gastropoda/HYDATINIDAE.html
http://slugsite.us/bow/hov99_1a.htm
http://www.ne.jp/asahi/kappa-kuri/miyamoto/OSEHOO/umiushi114.html
http://slugsite.us/bow/wirtz00/cvi_7a.htm
http://www.medslugs.de/E/Atl-E/Hydatina_physis.htm
http://www.vibrantsea.net/physis31_anilao10.html
http://www.medslugs.de/E/Ind-NW/Hydatina_physis.htm
http://www.sea-slug.com/species/umiusi013.htm
http://www.umiushi.info/photo_species/photo_splist_eng.php?sopt=0&loc=0000
http://www.medslugs.de/E/Pac-NW/Hydatina_physis.htm
http://www.Philippine-Sea-Slugs.com/CEPHALASPIDEA/Hydatina_physis.htm
http://www.medslugs.de/E/Pac-W/Hydatina_physis.htm
http://seaslugs.free.fr/nudibranche/a_hyda_physis.htm
http://www.jaxshells.org/phy04.htm
http://www.medslugs.de/E/Atl-W/Hydatina_physis.htm
http://www.seaslugsofhawaii.com/species/Hydatina-physis-a.html
http://www.nudibranch.com.au/pages/7179b.htm
http://www.underwaterkwaj.com/nudi/cephalaspideans/e129.htm
http://www.underwaterkwaj.com/nudi/hawaii/hc07.htm