The term 'Class of Animals' can be broken down into two crossword solutions: GENUS (5 letters) and SPECIES (7 letters). GENUS is a taxonomic rank used in the classification of living and fossil organisms, which is generally composed of a group of SPECIES exhibiting similar characteristics. SPECIES is a taxonomic rank below GENUS, and is the most specific classification of organisms. It is a group of organisms that are capable of interbreeding and producing fertile offspring.