The number of species in phylum Arthropoda $\left(\mathrm{A}\right)$ is more than 1.3 billion because insects form the most species-rich taxonomic group (>70% of the total animals). Phylum Mollusca $\left(\mathrm{C}\right)$ is the second largest phylum with approximately 90000+ species. Phylum Chordata $\left(\mathrm{B}\right)$ has approximately 60,000 species, among which, half of the species are fishes.