Question

Name two protostome phyla. What characteristics do these phyla share?

Briefly contrast the body plan of a basal animal (i.e. porifera or cnidarians) with that of a chordate.

Answer 1

Protostome means in which the blastopore becomes mouth. Two protostomes phyla are Annelida and Arthropoda.

Shared characteristics of Annelida and Arthropoda:

a. Both Phylum have three germ layers - Outer Ectoderm, middle mesoderm and inner endoderm.

b. Both have true coelom or body cavity.

c. Both phyla have mouth at the anterior end and anal opening at the posterior end.

d. Annelida and arthropoda both have sexual reproduction and fertilization can be external or internal.

e. Both the phylum have brain at the anterior end and both have ventral nerve cord situated along the length of the body.

Difference in body plan between Cnidaria and Chordata:

1. Cnidaria have no true coelom, where as chordate have true coelom

2. Cnidaria is diploblastic which means they have two body layers such as ectoderm and endoderm. There exis a jelly like mesoglea between ectoderm and endoderm in cnidaria. Chordates are triploblastic and they have Outer Ectoderm, middle mesoderm and inner endoderm.

3. In Cnidaria The mouth have originated from blastopore which means they are protostomes where as Chordates are Deuterostomes which means blastopore develops into anal opening.

4. Most of Cnidaria have radial symmetry which means their body can be cut in two equal halves by any plane going through the centre point where as chordates have bilateral symmetry which means they can be separated in two equal halves by only one central axis.