In addition to the scarcity of cell lines from marine vertebrates, a persistent absence of cell lines from non-arthropod invertebrates has stymied research on many valuable species useful in comparative genomics and a variety of other disciplines (Bayne 1998; Rinkevich 1999) . Selection of the echinoderm Strongylocentrotus purpuratus (purple sea urchin) as a model species for genomic sequencing has enhanced the need for cell lines from this species in particular. We recently have explored cell culture using both this species and the closely related Strongylocentrotus droebachi- ensis (green sea urchin). Cells from Polian vesicles and axial organ (Figures 6 and 7) appear to have proliferated in vitro for more than 8 months (Parton and Bayne 2004, 2005) . Other cultures yielded thraustochytrid protists that are common parasites of marine invertebrates worldwide (Rinkevich 1999) . Basal nutrient culture medium was LDF diluted with 4 volumes of filtered sea water (Kawamura and Fujiwara 1995) with antibiotics (penicillin 200 U/ml, streptomycin 200 lg/ ml, ampicillin 25 lg/ml), sodium bicarbonate at 0.18 g/l and HEPES at 15 mM. Culture vessels were held at 20°C in ambient air. Additives included fetal calf serum (heat inactivated) at 1-3%; insulin at 10 lg/ml; transferrin at 10 lg/ml; FGF at 50 ng/ml; EGF at 50 ng/ml; b-mercapto-etha-nol at 55 lM; chemically defined lipid supplement at 1 ll/ml; selenium at 10 nM, and L-glutamine at 200 lM.