Question

This Roman snail, this cuttlefish, and this mussel have similarities and differences in their body structures. What does the information about these structures tell you about the ancestors of these species

Answer 1

Complete question:

This Roman snail, this cuttlefish, and this mussel have similarities and

differences in their body structures. What does the information about these

structures tell you about the ancestors of these species?

a) None share an ancestor population because different species cannot share  an ancestor population. It is a coincidence that these species have some of  the same body structures.

b) The Roman snail and the cuttlefish share an ancestor population, but they  must not share an ancestor with mussels because mussels have no radula.

c) All three species share an ancestor population, but Roman snails and

cuttlefish share a more recent ancestor population. This is why they share

the radula structure.

d) We cannot make observations of ancestor populations from the past. It is

impossible to explain ancestors with only the information about the body

structures of different species.

Answer:

The correct answer is option C. All three species share an ancestor population, but Roman snails and  cuttlefish share a more recent ancestor population. This is why they share  the radula structure.

Explanation:

The three species belong to the mollusk phylum, and to the placophore group.

Each of them belongs to a different class.

• The Roman snail belongs to the Gasteropod class,
• The cuttlefish belongs to the Cephalopod class,
• The mussel belongs to the Bivalve class.

The tree classes share a common ancestor from which all the placophores evolved. Among them, we can mention the monoplacophore, gasteropod, cephalopod, bivalve, and scaphopods. Three branches diverged from this common ancestor. The first one originated the monoplacophore. The second one originated the common ancestor of gastropods and cephalopods. And the third one originated the common ancestor of bivalves and scaphopods. The tree-mentioned species inherited the mantle and the radula from their foreign common ancestor. But later in time, individuals that originated bivalves lost the radulla. This is why the three species have a mantle, but only gastropods and cephalopods have a radula. When each of these classes evolved, they developed their own traits,

• Gastropods → muscular foot used for moving  
• Cephalopods → pallial cavity for swimming
• Bivalves → byssal threads to attach to the rocks

You will find an image in the attached files that will help you understand this explanation.