Animal Phyla

Chordates are defined by specific developmental features like a notochord. Crabs are arthropods, which are invertebrates, and do not belong to the phylum Chordata.

All chordates possess a dorsal hollow nerve cord at some stage of their development. Features like hair, warm-bloodedness, or live birth are specific to certain classes, such as mammals, not all chordates.

Anemones are Cnidaria, slugs are Mollusca, and sponges are Porifera. This matches the classification provided in option B.

Crabs are Arthropoda, cuttlefish are Mollusca, and earthworms are Annelida. Option D correctly identifies these groups.

Platyhelminthes are flatworms characterized by their lack of body segments and a flattened body shape. Tapeworms are a classic example of this phylum.

Spiders have jointed legs and an exoskeleton, which are the primary defining characteristics of the phylum Arthropoda.

While many mollusks have shells, not all do (e.g., slugs and octopuses). Therefore, secreting a calcium carbonate shell is not a feature of all mollusks.

Snails are soft-bodied invertebrates that typically possess a mantle and a muscular foot, placing them in the phylum Mollusca.

Cnidarians are defined by specialized stinging cells called nematocysts, which they use for defense and capturing prey.

Porifera (sponges) are the simplest animals; they lack true tissues, organs, a mouth, and a digestive system, relying on water flow through pores for feeding.

Sponges are the sole members of the phylum Porifera, which means pore-bearing.