Final answer:
The animal species primarily threatened by extinction belong to the phylum Arthropoda, which encompasses diverse creatures like spiders, insects, and crabs.
Step-by-step explanation:
Animal species that are threatened by extinction are primarily in the phylum C. Arthropoda. Phylum Arthropoda includes a vast array of species including spiders, scorpions, crabs, barnacles, and insects. Many of these species face threats from habitat loss, pollution, and other anthropogenic factors. Out of the options provided, this phylum has the broadest representation of animal diversity and also includes many species currently threatened with extinction.