\\\\(\ extbf{Correct option: A}\\\\)\\\\(\ extbf{Solution:}\\\\)\\\\(\ extbf{Explanation for correct option:}\\\\)Option A:\\\\(\\bullet\\\\) Osteichthyes is a class having bony fishes i.e. their skeletal system is majorly made up of bone tissue.\\\\(\\bullet\\\\) These fishes have four pairs of gills covered by an operculum.\\\\(\ extbf{Explanation for incorrect options:}\\\\)Option B:\\\\(\\bullet\\\\) Chondrichthyes are the class of cartilaginous fishes i.e. their endoskeleton is made up of cartilage.\\\\(\\bullet\\\\) They have four-five pairs of gill slits which are not covered with the operculum.Option C:\\\\(\\bullet\\\\) Arthropoda is the phylum of kingdom Animalia and it contains all types of insects.\\\\(\\bullet\\\\) Metamerism is the characteristic of segmentation of the body into different metameres. It is found in annelids, arthropods, and chordates.\\\\(\\bullet\\\\) But excretion through nephridia is the characteristic of only annelids. Nephridial are the coiled tubular structures present all over the skin of annelids (earthworm) through which metabolic waste is excreted out of their body.Option D:\\\\(\\bullet\\\\) Platyhelminthes are commonly known as flatworms.\\\\(\\bullet\\\\) They have a flat body that can be divided into two equal halves by a single plane, thus, they possess bilateral symmetry.\\\\(\\bullet\\\\) Coelomate organisms possess a body cavity called coelom. But Platyhelminthes have a flat body so, they do not possess any body cavity. That means they are acoelomates.\\\\(\\bullet\\\\) Both \\\\(Taenia\\\\) and \\\\(Fasciola\\\\) are the examples of Platyhelminthes.Hence the correct option is option A.