» Calcareous Flowers: Tests and Cross-sections of Sea Urchin Spines.    Photographic study by Richard Howey with some fine photographs of the intricate beauty of these structures.    http://www.microscopy-uk.org.uk/mag/artaug05/rh-seaurchin.html

» Echinoid Directory    Biology, phylogeny, and classification of sea urchins.    http://www.nhm.ac.uk/research-curation/projects/echinoid-directory/intro/introduction.html

» Heart Urchin: Abatus sp.    Photographs and information on several species of heart urchin found in McMurdo Sound in Antarctica.    http://www.peterbrueggeman.com/nsf/fguide/echinodermata5.html

» Loxechinus albus    Factsheet from the FAO on the Chilean Sea Urchin which is eaten in Chile and Peru, its distinguishing features, distribution, habitat and biology.    http://www.fao.org/fi/website/FIRetrieveAction.do?dom=species&fid=3621

» MSN Learning & Research Plus: Sea Urchin    Online encyclopedia article.    http://encarta.msn.com/encnet/refpages/RefArticle.aspx?refid=761560371

» Pencil Urchin: Ctenocidaris perrieri    Photographs and information on this urchin found in the icy waters of Antarctica.    http://www.peterbrueggeman.com/nsf/fguide/echinodermata20.html

» Photos of Sea Urchins    Photos of Echinoidea from the Indo-Pacific, with text about behavior, habitat, and characteristics.    http://www.starfish.ch/collection/seeigel.html

» Red Sea Urchin    Information from Wikipedia on this species, Strongylocentrotus franciscanus, including its description, feeding habits, behavior and reproduction.    http://en.wikipedia.org/wiki/Red_sea_urchin

» Sea Urchin Embryo    A page from the Laboratory of Embryonic Gene Expression, included here for three beautiful photographs.    http://www.its.caltech.edu/~mirsky/

» Sea Urchin Embryology    Laboratory modules using sea urchin eggs to explore fertilization and development.    http://www.stanford.edu/group/Urchin/

» Sea Urchin: A Stinging but Amazing Animal    Article by Jean-Marie Cavanihac on these animals with many photographs of their development.    http://www.microscopy-uk.org.uk/mag/artjul00/urchin1.html

» Sea Urchins Revisited    Photographic study by Jean-Marie Cavanihac of the sea urchin with some microscopic features of interest to the amateur naturalist.    http://www.microscopy-uk.org.uk/mag/artmay02/urchin2.html

» Sterechinus neumayeri    Photographs and information on this urchin found in Antarctica which often camouflages itself with bits of shell and debris.    http://www.peterbrueggeman.com/nsf/fguide/echinodermata1.html

» Strongylocentrotus drobachiensis    Exercise from Invertebrate Anatomy OnLine covering the systematics, external and internal anatomy of the green sea urchin.    http://webs.lander.edu/rsfox/invertebrates/strongylocentrotus.html

» Strongylocentrotus purpuratus    Photograph and information on the purple sea urchin.    http://digimorph.org/specimens/Strongylocentrotus_purpuratus/

» The Echinoids    Information about sea urchins, such as how they live, feed, and reproduce. There is also an alphabetic listing of their taxa. From The Natural History Museum, London.    http://www.nhm.ac.uk/palaeontology/echinoids/

» Who is in Charge Here?    Illustrated article by Richard L. Howey considering how creatures with no brains, such as the sea urchin, react appropriately to their surroundings.    http://www.microscopy-uk.org.uk/mag/artdec02/rhcharge.html