Most animals reproduce sexually, although this is not a great standard to define animals as some frogs can reproduce asexually by changing gender. Other animals can also breed asexually.

It is the cells that most accurately distinguish animals from other kingdoms. Animal cells have both a membrane-bound nucleus and organized mitochondria, which are lacking in monerans. They are many-celled, not single-celled (even hydras are several cells thick) which distinguishes them from most protists and monerans.

There are at least 35 phyla (pl for phylum) in this kingdom, with more waiting to be discovered:

Acanthocephala (thorny-headed worms) 500 spp
Acoela (gutless flatworms)
Annelida (segmented worms) 8700 spp
Arthropoda (crustaceans, insects, spiders, ticks, scorpions) 838000 spp
Brachiopoda (lampshells) 230 spp
Bryozoa or Ectoprocta (colonial moss animals) 3500 spp
Chaetognatha (arrowworms) 50 spp
Chordata (fish, birds, mammals, reptiles, amphibians, sharks, sea squirts) 44000 spp
Cnidaria (jellyfish, hydra, coral) 9200 spp (also known as Coelenterata)
Ctenophora (comb-jellies) 80 spp
Cycliophora (pandoras) 1 spp
Echinodermata (starfish, sea urchins, sand dollars) 600 spp
Echiura (spoon worms) 150 spp
Endoprocta (moss animals) 75 spp
Gastrotricha (gastrotrichs) 170 spp
Gnathostomulida (gnathostomulids) 80 spp
Hemichordata (acorn worms, pterobranchs) 230 spp
Kinorhyncha (kinorhynchs) 150 spp
Loricifera (sediment dwellers)
Mesozoa (small, worm-like animals) 50 spp
Mollusca (snails, slugs, clams, octopi) 50000 spp
Nematoda (nematodes) 10000 spp
Nematomorpha (horsehair worms) 230 spp
Onychophora (velvet worms) 90 spp
Pentastoma (tongue worms) 70 spp
Phoronida (phoronids) 15 spp
Placozoa (Trichoplax) 2 spp
Platyhelminthes (flatworms) 13000 spp
Pogonophora (beardworms) 80 spp
Porifera (sponges) 4800 spp
Priapulida (small, spiny-headed worms) 9 spp
Rhynchocoela or Nemertina (ribbon worms) 800 spp
Rotifera (rotifers) 2000 spp
Sipuncula (peanut worms) 250 spp
Tardigrada (tardigrades) 400 spp