Tissues tightlystructural and functional units organized by groups of similar cellular telephone ; sponge lackmany tissue types found in animals however science recently showed that onegroup of sponges has an epithelium . blastopore. Opening in blastula that becomes the backtalk or 1 sense of anu. Ectoblast gave hike to skin and the nervous system. 1. provides space for uids to circulate among organs with in the mesoderm 2. provides a hydrostatic underframe for movement: other structures ful ll these functions in arthropods and mollusk (hemocoel, exoskeleton , visceral mass ). Absent in at worms and reduced in mollusks and arthropods what is unusual about echinoderm symmetry? echinoderms have two different correspondence . they are bilaterally symmetric as larvae, and radially symmetric as grownup . Choano agellates chemical group of protists which are the closest living relatives of animals. Features that allowed the passage to land the key featureswere supporting their torso free weight , and movement on land.