Animal (Animalia) groups {division, animals} are mostly invertebrates.
properties
Animals (Eumetazoa) (Metazoa) can have many eukaryotic cells. Animals digest internally {heterotrophic}. Animal cells have no cell walls. Animals can move. Embryos have blastula stage.
evolution
Animals evolved from eukaryotic collared flagellates {choanoflagellates}. Some sponges have choanocytes.
Choanoflagellates, fungi, and parasitic protists {opisthokonts} have posterior flagellum, as sperm do. Other eukaryotes have anterior flagellum or no flagellum.
Comb jellies were the first animals, and other animals evolved from them.
symmetry
Animals can have bilateral symmetry (Bilateria) or radial symmetry.
Placozoans have no symmetry.
Ctenophores and Cnidaria are radially symmetric. Echinoderms are radially symmetric.
symmetry: bilateral
Protostomes and deuterostomes are Bilateria.
Orthonectids (Orthonectida), rhombozoans (Rhombozoa), Myxozoa, Acoelomorpha, and cycliophora are Bilateria but are not protostomes or deuterostomes.
archenteron
Animals can open first {archenteron} at mouth (Protostomia) or first at anus (Deuterostomia).
coelom
Protostomes have mesoderm from gastrula interior {schizocoelous development}. Deuterostomes have mesoderm from endoderm invagination {enterocoelic pouching}.
protostomes
Protostomes are Lophotrochozoa, Trochozoa or Platyzoa, or Ecdysozoa.
Lophotrochozoa are segmented annelids worms and molluscs, plus arrow worms, bryozoans and ectoprocts and moss animals, entroprocts, gastrotrichs, lampshells, lophophorates, phoronids, proboscis worms, and sipunculan worms.
Trochozoa are flatworms and rotifers, plus spiny-headed worms, gnathostomulida, micrognathozoa, and cycliophora.
Ecdysozoa are ciliated protozoans, comb jellies or ctenophors, cnidarians or coelenterates, sponges, nematodes, and arthropods, plus gordian worms and horsehair worms, kinorhynchs, loriciferans, placozoa, priapulans, velvet worms, and water bears.
protostomes: evolution
From protostomes came Schizocoelia, Bryozoa, Parenchymia, and Gnathifera (Spiralia) and Gastrotricha, Introverta, and Cephaloryncha (Cycloneuralia).
Schizocoelia are Sipuncula and Articulata: Mollusca, Annelida, and Panarthropoda. Panarthropoda are Onchyophora, Tardigrada, and Arthopoda.
Bryozoa are Ectoprocta and Entoprocta.
Parenchymia are Nemertini and Platyhelminthes.
Gnathifera are Rotifera, Gnathostomulida, and Chaetognatha.
Introverta are Nematoda and Nematomorpha.
Cephaloryncha are Priapulida, Kinorhyncha, and Loricifera.
deuterostomes
Deuterostomes are echinoderms, acorn worms or hemichordates, and chordates, plus gnathostomulids.
deuterostomes: evolution
Echinodermata and Pterobranchia ancestors and Phoronida and Brachiopoda ancestors split.
Hemichordata ancestors and Echinodermata and Pterobranchia ancestors split.
Chordata ancestors and Hemichordata ancestors split.
invertebrates
Major invertebrates are protozoa (Protozoa), sponges (Porifera), jellyfish and corals (Coelenterata), hydroids (Hydroida), flatworms (Platyhelmintha), roundworms (Nematoda), earthworms (Annelida), insects and crustaceans (Arthropoda), clams (Mollusca), and starfish (Enchinodermata). Minor invertebrates are acorn worms, clictors, ctenophors, gastrotricha, lampshells, moss animals, phoronids, proboscis worms, rotifers, sipunculans, and velvet worms or onychophora.
vertebrates
Chordates include vertebrates. Vertebrates split from Ecdysozoa.
Animal classes {classification, animal} can depend on body organization.
cell differentiation
Animal cells differentiate into tissues and organs in patterns.
symmetry
Animals differ in symmetry: radial or axial.
body cavity
Animals differ in body cavity. Some animals have one cavity with mouth opening. Some animals have alimentary canal tube from mouth to anus, surrounded by coelom tube from mouth to anus.
segmentation
Animals differ in body-segment number and differentiation.
nervous system
Animals differ in body and nervous-system structure.
Number of repeated body structures {segmentation, body}| can differ.
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Date Modified: 2022.0225