Among protostomes, which morphological trait has shown the most variation?
A. Type of symmetry (bilateral vs. radial vs. none)
B. Type of body cavity (coelom vs. Pseudocoelom vs. acoelom)
C. Number of embryonic tissue types (diploblastic vs. triploblastic)
D. Cephalization (head vs. no head)
I think it is B but can someone please confirm it for me???
It's B
To determine which morphological trait has shown the most variation among protostomes, we can break down each option and analyze the potential variation:
A. Type of symmetry (bilateral vs. radial vs. none): This refers to the organization of body parts around a central axis. Although there are organisms with radial and no symmetry among protostomes (such as sea anemones or sponges), the majority of protostomes exhibit bilateral symmetry. However, when comparing the variation between bilateral organisms, there is relatively less variation compared to other traits.
B. Type of body cavity (coelom vs. Pseudocoelom vs. acoelom): This refers to the presence and organization of a fluid-filled cavity within the body. Coelom is a true body cavity, pseudocoelom is a partially lined body cavity, and acoelom refers to organisms lacking a body cavity. There is indeed considerable variation in the presence and organization of body cavities among protostomes, making this a viable option for the trait with the most variation.
C. Number of embryonic tissue types (diploblastic vs. triploblastic): This refers to the number of primary germ layers during embryonic development. Diploblastic organisms have two germ layers (ectoderm and endoderm), while triploblastic organisms have three germ layers (ectoderm, mesoderm, and endoderm). The majority of protostomes are triploblastic, with relatively little variation among them.
D. Cephalization (head vs. no head): This refers to the concentration of sensory organs and nervous tissue in the anterior end of an organism. While some protostomes (e.g., flatworms) show a high level of cephalization, others (e.g., cnidarians) show a less pronounced or no head region. The variation in cephalization among protostomes is significant but not as extensive as the variation in other traits.
Considering the above analysis, option B, the type of body cavity, is indeed the correct answer.