What is an Invertebrate?

The majority of animal species on Earth are invertebrates.  Invertebrates lack a rigid jointed internal skeleton.  They range in size from microscopic organisms to the giant squid, the largest of which was 59 feet, weighing nearly one ton.

There are 37 phyla in the Animal Kingdom:

• • Ctenophora – Comb Jellies (242 species)
  • Porifera – Sponges (8,346 species)
  • Placozoa – Placozoan (1 species)
  • Cnidaria – Cnidarians (10,105 species)
  • Myxozoa – Myxozoans (2,402 species)
  • Xenoturbellida – Strange Worms (2 species)
  • Acoelomorpha – Acoelomorphs (393 species)
  • Orthonectida – Orthonectids (43 species)
  • Rhombozoa – Rhombozoans (123 species)
  • Echinodermata – Echinoderms (20,509 species)
  • Hemichordata – Hemichordates (120 species)
  • Chaetognatha – Arrow Worms (186 species)
  • Nematoda – Roundworms (24,783 species)
  • Nematomorpha – Horsehair Worms (351 species)
  • Tardigrada – Water Bears (1,157 species)
  • Onychophora – Velvet Worms (182 species)
  • Arthropoda – Arthropods (1,242,040 species)
  • Priapulida – Priapulid Worms (19 species)
  • Loricifera – Girdle Wearers (30 species)
  • Kinorhyncha – Mud Dragons (179 species)
  • Bryozoa – Moss Animals (10,941 species)
  • Entoprocta – Goblet Worms(169 species)
  • Cycliophora – Clycliophorans (2 species)
  • Annelida – Segmented Worms (17,210 species)
  • Spincula – Peanut Worms (1,507 species)
  • Echiura – Spoon Worms (236 species)
  • Mollusca – Mollusks (117,358 species)
  • Nemertea – Ribbon Worms(1,200 species)
  • Brachiopoda – Lamp Shells (443 species)
  • Phoronida – Horseshoe Worms (10 species)
  • Gastrotricha – Gastrothichs (790 species)
  • Platyhelminthes – Flatworms (29,285 species)
  • Gnathostomulida – Jaw Worms (109 species)
  • Micrognathozoa – Micrognathozoa (1 species)
  • Rotifera – Rotifers (1,583 species)
  • Acanthocephala – Spiny-headed Worms (1,194 species)
  • Chordata – Chordates
  • Cephalochordata – Lancelets (33 species)
  • Tunicata/Urochordata – Tunicates (2,792 species)
  • Craniata/Vertebrata – Vertebrates (64,832 species)

Based on Zhang, Z.-Q. 2011. Animal biodiversity: An introduction to higher-level classification and taxonomic richness. Zootaxa 3148: 7–12.