Question

which organisms are a phylum of soft-bodied animals, many of which are protected by a hard shell?
a) sponges
b) chordates
c) cnidarians
d) mollusks
e) roundworms
f) echinoderms
g) flatworms
h) arthropods
i) annelids

Explanation:

Mollusks are a phylum of soft - bodied animals. Many mollusks, such as snails and clams, have a hard shell that provides protection. Sponges (a) are simple, porous animals without a shell. Chordates (b) include vertebrates like humans and have a notochord at some stage of development, not a shell for protection in the way described. Cnidarians (c) like jellyfish have stinging cells but no hard shell. Roundworms (e), flatworms (g), annelids (i) are worms and do not have the characteristic hard - shelled protection of mollusks. Echinoderms (f) like starfish have a spiny exoskeleton, not a shell in the traditional sense. Arthropods (h) have an exoskeleton made of chitin, which is different from the calcium - based shells of mollusks.

Answer:

d) mollusks