Try looking up sea squirts (Tunicata), acorn worms (Enteropneusta) and Pterobranchia. Oh, and Branchiostoma of course, the lancelet. And in some ways hagfish aren´t considered real vertebrates either.

There are many Phyla in Animalia, there are quite a few small phyla that many scientists argue over how to classify.

So the larger Phyla are:

Porifera - Sponges

Cnidaria - Jellyfish, Corals

Ctenophora - Comb Jellies

Platyhelminthes - Flatworms - Tapeworms

Nematoda - Round worms - Hookworms

Nemertea - Ribbon Worms

Acanthocephala - Spike headed worms

Bryozoa - Mossy corals

Tardigrada - Water Bears

Brachiopoda - Primtive Bivalves

Mollusca - Clams Mussles

Annelida - Segmented worms - Earth worms

Sipuncula - Peanut Worms

Arthropoda - insects - millipedes - centipedes - spiders - crabs

Chaetognatha - Arrow Worms

Echinodermata - Sea Stars- Urchins - Sea Cucumbers

Hemichordata- Acorn Worms

Chordata - Reptiles Fish Birds Mammals

Some of the smaller and debated ones include:

Placazoa

Kinorhyncha - Mud Dragons

Priapulida

Loricifera

Nematomorpha - Horsehair worms

Onychophora - Velvet worms

Gastrotricha

Rotifera - Rotifers

Cycliophora

Phoronida - Horseshoe worms

Pterobranchia

There are more or less depending on what book or site you check out, or what scientist you talk to.