A SIMPLIFIED current probable phylogenetic tree of invertebrate phyla:
 
 
PHYLUM
Protozoans unicellular-animals
Unicellular
Poriferans sponges
Cnidarians e.g jellyfish,corals
Diploblasts/Radiata
Platyhelminthes  flatworms 
Rotifers wheeled animals
Triploblasts/Bilateria Molluscs e.g. clams, squid
Annelids  segmented worms
 Lophotrochozoa
Bryozoans moss animals
Ecdysozoa Arthropods e.g. crabs, insects
Nematodes round worms
Echinoderms e.g. starfish
Deuterostoma
Chordates e.g. fish, mammals

Absolute horizontal distance on the above diagram does not imply relative evolutionary time since divergences.  Instead, the diagram above should only be interpreted as order (sequence) of divergence within a particular taxonomic lineage.
 

Click here to see the old phylogenetic tree that Dr. D. learned in the Dark Ages

Click here to compare with the modern full version with all animal phyla