Question

What is 'tissue' level of organisation among animals? Which metazoans do exhibit this organisation?

Answer 1

The lev. of org. in which division of labour is amongst the tissues is known as tissue lev. of org.
It is seen in CNIDARIA and CTENOPHORA

Answer 2

Tissues are groups of similar cells that have a common function. The four basic tissue types are epithelial, muscle, connective, and nervous tissue. Each tissue type has a characteristic role in the body:

i. Epithelium covers the body surface and lines body cavities.

ii. Muscle provides movement.  

iii. Connective tissue supports and protects body organs.  

iv. Nervous tissue provides a means of rapid internal communication by transmitting electrical impulses.

Platyhelminths are the first bilaterally symmetrical, acoelomate metazoans to have reached the tissue-organ level of organization. Further all Acoelomates, pseudocoelomate, cellmates have this organization.