Question

The phyla of diploblastic animals are
(A) Porifera and Cnidaria
(B) Cnidaria and Platyhelminthes
(C) Ctenophora and Platyhelminthes
(D) None of the above

Answer 1

The animals belonging to the diploblastic category do not have specified body cavities. They show the presence of two germ layers and exhibit increased complexity. Jellyfishes, sea anemone are diploblastic.

Complete answer:
The diploblastic is the condition of blastula in which the organism contains two germinal layers, named as ectoderm (outer layer) and endoderm (inner layer). The endoderm develops into tissues whereas the ectoderm forms nervous tissues, epidermis and other organs like nephridia. The diploblastic animals lack organ level of organisation.

Let us discuss the given options-
A) The Cnidarians comprises gastrodermis (inner layer) and epidermis (outer layer), whereas the Poriferans comprises choanoderm (inner layer) and pinacoderm (outer layer). Both the Cnidarians and Poriferans possess two germ layers including endoderm and ectoderm. Hence diploblastic. The Cnidarians include organisms like jellyfish, corals. The porifera includes animals like sponges.
B) Platyhelminthes- These organisms are triploblastic in which the body comprises three germ layers- endoderm, ectoderm and mesoderm. They exhibit bilateral symmetry. Example flatworms.
C) Ctenophora-Some species of Ctenophora are triploblastic whereas some are diploblastic. Example- comb jelly.

Additional information: The diploblastic organisms are radially symmetrical whereas the triploblastic are bilaterally symmetrical. The diploblastic and triploblastic animals differ in the type of cleavage during the embryo formation.

Thus, the correct answer is option ‘A’.

Note: The triploblastic organisms develop into three germ layers. The third layer called the mesoderm develops into a true organ system. The triploblastic develop true body cavity called coelum. The coelum acts as a shock absorber for the organs. The organisms starting from flat worms to humans are triploblastic.