What is the best way to classify two different organisms that have similar appearance and are found in the same environment?

Determine the DNA differences

The main difference between DNA and RNA is their chemical composition namely in their sugar and pyrimidine bases. DNA has the bases adenine, guanine, cytosine, thymine and the sugar deoxyribose. RNA has the bases adenine, guanine, cytosine and uracil and the sugarribose. Besides differing chemically, RNA is usually single stranded while most DNA is usually double stranded forming a double helix. An RNA strand can coil back on itself to form a hairpin-shaped structure with complementary base pairing and helical organization.