Which of the following groups of animals is classified under the phylum Arthropoda?

The correct answer is a group that includes insects, crustaceans, and spiders, all of which belong to the phylum Arthropoda. This phylum is characterized by animals that have an exoskeleton made of chitin, segmented bodies, and jointed appendages. Each of these groups possesses these defining traits.

Insects, which number in the millions of species, have three main body segments: the head, thorax, and abdomen, along with three pairs of legs and usually one or two pairs of wings. Crustaceans, such as crabs and lobsters, are primarily aquatic and are characterized by having a carapace covering their bodies and multiple pairs of appendages that often include specialized structures for feeding and locomotion. Spiders are arachnids and have two main body segments, eight legs, and no antennae.

The other groups listed do not fall under the phylum Arthropoda: sea urchins and starfish are echinoderms, worms belong to various phyla, including Annelida or Nematoda, and reptiles and amphibians are classified under the phylum Chordata. Each of these groups has distinct biological characteristics that set them apart from arthropods.