http://tolweb.org/treehouses/?treehouse_id=4879
http://www.arkive.org/purple-sea-urchin/strongylocentrotus-purpuratus/
http://www.ucmp.berkeley.edu/exhibits/biomes/marine.php
http://animaldiversity.ummz.umich.edu/accounts/Strongylocentrotus_purpuratus/
http://www.enchantedlearning.com/subjects/invertebrates/echinoderm/Purpleseaurchin.shtml
http://education.nationalgeographic.com/education/encyclopedia/food-web/?ar_a=1
http://www.asnailsodyssey.com/LEARNABOUT/URCHIN/urchRepr.php
http://neilhorton.hubpages.com/hub/Carrying-Capacities-of-Populations
http://factsanddetails.com/world.php?itemid=1257&catid=53&subcatid=338
http://www.sanctuarysimon.net/species/species_info.php?speciesID=188&search=name&taxonomicGroup=&name=Purple%20sea%20urchin
http://library.thinkquest.org/J002608/urchin.html
http://www.montereybayaquarium.org/animals/AnimalDetails.aspx?id=781774
http://www.untamedscience.com/biodiversity/animals/echinodermata/sea-urchins/echinoida/strongylocentrotidae/strongylocentrotus/purple-sea-urchin
http://www.ehow.com/about_6463774_life-cycle-purple-sea-urchin.html
http://www.vichighmarine.ca/reports/sea-stars-and-relatives/purple-sea-urchin
http://www.biolbull.org/content/128/2/169.abstract
http://www.sciencedaily.com/videos/2007/0304-sea_urchins_reveal_medical_mysteries.htm
http://www.aip.org/dbis/stories/2007/17032.html
http://en.wikipedia.org/wiki/Purple_sea_urchin
http://w3.shorecrest.org/~Lisa_Peck/MarineBio/syllabus/ch7invertebrates/Invertwp/echino_wp_06/mike/seaurchinbiology.htm
http://en.wikipedia.org/wiki/Sea_urchin
http://www.stanford.edu/group/Urchin/adult.html
http://www.arkive.org/purple-sea-urchin/strongylocentrotus-purpuratus/
http://www.ucmp.berkeley.edu/exhibits/biomes/marine.php
http://animaldiversity.ummz.umich.edu/accounts/Strongylocentrotus_purpuratus/
http://www.enchantedlearning.com/subjects/invertebrates/echinoderm/Purpleseaurchin.shtml
http://education.nationalgeographic.com/education/encyclopedia/food-web/?ar_a=1
http://www.asnailsodyssey.com/LEARNABOUT/URCHIN/urchRepr.php
http://neilhorton.hubpages.com/hub/Carrying-Capacities-of-Populations
http://factsanddetails.com/world.php?itemid=1257&catid=53&subcatid=338
http://www.sanctuarysimon.net/species/species_info.php?speciesID=188&search=name&taxonomicGroup=&name=Purple%20sea%20urchin
http://library.thinkquest.org/J002608/urchin.html
http://www.montereybayaquarium.org/animals/AnimalDetails.aspx?id=781774
http://www.untamedscience.com/biodiversity/animals/echinodermata/sea-urchins/echinoida/strongylocentrotidae/strongylocentrotus/purple-sea-urchin
http://www.ehow.com/about_6463774_life-cycle-purple-sea-urchin.html
http://www.vichighmarine.ca/reports/sea-stars-and-relatives/purple-sea-urchin
http://www.biolbull.org/content/128/2/169.abstract
http://www.sciencedaily.com/videos/2007/0304-sea_urchins_reveal_medical_mysteries.htm
http://www.aip.org/dbis/stories/2007/17032.html
http://en.wikipedia.org/wiki/Purple_sea_urchin
http://w3.shorecrest.org/~Lisa_Peck/MarineBio/syllabus/ch7invertebrates/Invertwp/echino_wp_06/mike/seaurchinbiology.htm
http://en.wikipedia.org/wiki/Sea_urchin
http://www.stanford.edu/group/Urchin/adult.html