Mammals are invertebrates.
Cortical granules are regulatory secretory organelles ( ranging from 0.2 um to 0.6 um in diameter ) found within oocytes and are most associated with polyspermy prevention after the event of fertilization . Mammals are any vertebrates within the class Mammalia ( [ məˈmeɪli.ə ] from Latin mamma #Latin `` breast '' ) , a clade of endothermic amniotes distinguished from reptiles ( including birds ) by the possession of a neocortex ( a region of the brain ) , hair , three middle ear bones and mammary glands .