In examining an unknown animal species during its embryonic development, how can you be sure what you are looking at is a protostome and not a deuterostome?
A) There is evidence of cephalization.
B) The animal is triploblastic.
C) The animal is clearly bilaterally symmetrical.
D) You see a mouth, but not an anus.

Question

Quizplus · Accepted Answer

One of the main defining characteristics of protostomes is that they develop a mouth before an anus, whereas deuterostomes develop an anus before a mouth. Therefore, if you observe a mouth but not an anus during embryonic development, you can be sure that you are looking at a protostome. The other three options (cephalization, triploblastic, and bilateral symmetry) are all characteristics shared by both protostomes and deuterostomes and are not sufficient to distinguish between the two.

In Examining an Unknown Animal Species During Its Embryonic Development