The Purple Sea Urchin has 44 chromosomes. The American Lobster (which is in the trophic level above the Purple Sea Urchin) has 100 chromosomes. We use the Purple Sea Urchin for research on trying to cure medical conditions such as Cancer, Alzheimer's and Infertility. We use them because we have many of the same genes and their genomes are very similar to ours.
Video: http://www.sciencedaily.com/videos/2007/0304-sea_urchins_reveal_medical_mysteries.htm
Video: http://www.sciencedaily.com/videos/2007/0304-sea_urchins_reveal_medical_mysteries.htm