The unknown multicellular organism with an endoskeleton most likely belongs to the kingdom Animalia. Thus, the correct option is C.
What is Kingdom?
Kingdom may be defined as a taxonomic classification of the second-highest rank, just below the domain and above the phylum.
Endoskeleton is found in the kingdom Animalia and refers to the skeletons which are present inside the body of the organisms that provide structural support and protection and assist them in migration.
Therefore, the correct option is C.
To learn more about Endoskeletons, refer to the link:
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