Nonsense of Noah
The actual number of animals on board the Ark would number in the billions if the command was taken literally. This would include the standard vertebrates but also, dinosaurs, insects, millions of bacteria and thousands of extinct species that, according to young earth proponents, died after the flood.
According to the latest counts, scientists agree that there are between 1.5 - 10 million species of animals, plants and algae. The conventional image of Noah's animals is of Koala bears, giraffes and elephants. Noah believers ignore the rest of the "animal" kingdom, i.e. the rest of the Vertebrate Animals and the Invertebrates
Biologists have great difficulty in defining a species. See Definition of Species in Wikipedia.Bearing in mind the problems with categorizing species, the following numbers are only a soft guide.
Total number of species living today (estimated):
Between 2 and - 100 millions (identified and unidentified), including:
5-10 million bacteria
Of the identified eukaryote species we have:
1.6 million, including:
297,326 plants, including:
13,025 Ferns and horsetails,
9,671 Red and green algae,
28,849 fungi & other non-animals, including:
2,849 brown algae,
1,250,000 animals, including:
+ 1,203,375 invertebrates:
+ 59,811 vertebrates:
So, it looks like there are about 59,811 vertebrates, 29,000 of which were fish leaving 30,000 species.
We take two of all unclean so lets say that most are unclean so 2 x 25,000 = 50,000 unclean animals.
We take seven pairs of the clean animal species so 7 x 2 x 5000 = 70,000 clean animals.
TOTAL for Vertebrate Animals 50,000 unclean, 70,000 clean = 120,000.
TOTAL Invertebrates: Insects and bacteria: 5 Million bacteria, 950,000 of every creeping thing of the earth after his kind.
Now, if you think theses numbers are too high, then lower them.
But then you have to explain how whatever was not on board the Ark, is here with us today.
PROBLEM WITH EXTINCT SPECIES
BUT... this number is for species living today.
Remember that according to some Christian apologists, the flood was responsible for depositing the fossil layers. The consequence of this hypothesis is the requirement for every species, including those believed to have become extinct millions of years ago, to be present at the time of the flood in order to deposit their share of fossils in the geological column.
If they were present, then Noah would have had to have two of each of them on the Ark.
A rough estimate of that number is that only 1 in 100 species is alive today; in other words, for every species living today, there were 99 species that have become extinct. Two of each of these extinct species would have had to have been on the Ark too. See Extinct Species
TOTAL NUMBER OF ANIMALS THAT SHOULD HAVE BEEN ON THE ARK
 In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are often used, such as based on similarity of DNA or morphology.