The chart lists five common animals and the phylum each one belongs to. These phyla are classified into two larger groups based on how their early embryos look.

An image of a table showing 5 different kinds of animals, their common name, phylum name and early embryo.
Which pair of animals are least closely related based on these data?

A.
Squid and centipede
B.
Snake and earthworm
C.
Earthworm and centipede
D.
Sea cucumber and snake

1 answer

To determine which pair of animals is least closely related based on their phylum and early embryonic development, we would need to look at the phyla associated with each animal and their embryological characteristics.

Squid (Mollusca)
Centipede (Arthropoda)
Snake (Chordata)
Earthworm (Annelida)
Sea Cucumber (Echinodermata)

Phylum classification can reveal relationships:

Mollusca (squid) and Arthropoda (centipede) are both part of the group known as protostomes.
Chordata (snake) and Echinodermata (sea cucumber) are members of the group called deuterostomes.
Annelida (earthworm) is also a protostome like squid and centipede.

Based on this classification:

A (Squid and centipede): Both are protostomes, related but in different phyla.
B (Snake and earthworm): One is deuterostome (snake) and the other is protostome (earthworm), indicating they are less closely related.
C (Earthworm and centipede): Both are protostomes, thus more closely related.
D (Sea cucumber and snake): Both are deuterostomes, indicating closer relation than some other pairs.

The pair that is least closely related would be B (Snake and earthworm), as they belong to different developmental groups (deuterostomes vs protostomes).