1) Which two animal phyla are considered to be on the “multicellular” level of organization, lacking true tissues? How do you expect them to differ in their embryonic development compared to other animals?

2. During which stage of embryonic development is the blastopore and digestive cavity formed?

3. What are the three primary germ layers? Which is missing in diploblastic organisms?

4. What type of symmetry is associated with diploblastic organisms? Which phylum is the exception to this rule and why?

5. Describe the 3 main developmental differences between protostome and deuterostome animals.

1 answer-  Only phylum porifera is consedered to be multicellular and lacking true tissues. In cellular level of body organisation, cells are arranged as loose aggregate and division of labour occurs among the cells. while in higher(tissue or organ) level of body organisation work of single cell is replaced by the group of similar cells arranged in proper manner to carry out life processes.

2- answer The embryonic stage in which blastopore and digestive cavity are formed is gastrula. Blastopore is the opening by which the cavity of the gastrula communicates with the exterior which later evolves into mouth or rectum

3- answer Three primary germ layers are:-

1. Ectoderm
2. Mesoderm
3. Endoderm

In diploblastic organism, mesoderm is missing as the third germ layer, in place of it undifferentiated mesoglea is present in between ectoderm and endoderm; which is non living and can be gelatinous.

4- answer The symmetry associated with diploblastic organisms is radial symmetry, in which when the plane passing through the central axis of the body divide the animal into two identical halves.

The phylum which is exception to this rule is Echinodermata because echinoderms are triploblastic only larvae of echinoderms posses bilateral symmetry.

5- answer Developmental difference

PFA