Mammalia is named after the Latin word Mamma. The word Mammalia means mammals. They can range from the tiny Thai bat (1.5 grams) to the largest blue whale (130 metric tons). They have taken over the world. Humans are the greatest animals on earth. Their number of species is 6,000. 10 classes, 35 tribes and 138 species of mammals have been identified in Bangladesh. Dr. Siddiq Publications