During the same time period, the number of endangered insects rose by 209 percent, the number of endangered molluscs (a class including snails, slugs, mussels, squid and worms) rose by 135 percent, while endangered fish species increased by 167 percent and the number of endangered reptiles even rose by 245 percent. The number of threatened mammals (defined by the International Union for Conservation of Nature and Natural Resources as species listed as either critically endangered, endangered or vulnerable on the Red List) increased by only 21 percent between 20. But while animals like critically endangered orangutans or humpback dolphins are getting a lot of attention, the number of threatened mammals has not been rising as fast as in other animal classes. The number of threatened species is increasing.