Do mollusks use vertebrate sex steroids as reproductive hormones? Part I: Critical appraisal of the evidence for the presence, biosynthesis and uptake of steroids

► Evidence for endogenous formation of vertebrate steroids by mollusks is weak. ► Mollusks do not have genes for key enzymes or functional nuclear receptors. ► Vertebrate steroids are everywhere in the environment (even human skin). ► Mollusks are very efficient at absorbing and retaining vertebrate steroids. ► Contamination is the probable source of steroids, even under laboratory conditions.