Question

Refer to the given table illustrating the characteristics of the body plan of some invertebrate embryos.
Select the correct sequence which corresponds to the phyla represented with P, Q, R, S, and T.

• A. Platyhelminthes - Nematoda - Annelida - Echinodermata - Chordata
• B. Cnidaria - Nematoda - Platyhelminthes - Echinodermata - Annelida
• C. Cnidaria - Platyhelminthes - Nematoda - Echinodermata - Annelida
• D. Cnidaria - Platyhelminthes - Nematoda - Annelida - Echinodermata

Answer 1

Answer: (D)

P - Cnidarian's body is diploblastic, with two cell layers of the body wall separated by mesoglea, and shows radial symmetry. The body cavity (gastrovascular cavity) is sac-shaped, with one opening acting as both mouth and anus. This opening is surrounded by tentacles bearing thread cells.

Q - Platyhelminthes are free-living and parasitic unsegmented worms that are dorsoventrally flattened, triploblastic, acoelomate, bilaterally symmetrical, complex gut, but still incomplete; gut absent in parasitic species.

R - Nematoda has a bilaterally symmetrical body, triploblastic, complete gut with a subterminal anus, a body cavity is a pseudocoel.

S - Annelida are all bilaterally symmetrical animals, triploblastic, complete gut, have a metamerically segmented body with a true coelom called as schizo-coelom.

T - Echinodermata which are entero-coelomate in which the coelom forms from pouches pinched off of the digestive tract, triploblastic, complete gut, have a metamerically segmented body.

Hence the correct option is D.