moon shell: marine gastropods having smooth rounded shells that form short spires
seasnail: any of several creeping marine gastropods with a spirally coiled shell: whelks; tritons; moon shells; neritids
base pair: one of the pairs of chemical bases joined by hydrogen bonds that connect the complementary strands of a DNA molecule or of an RNA molecule that has two strands; the base pairs are adenine with thymine and guanine with cytosine in DNA and adenine with uracil and guanine with cytosine in RNA