Phylogeny of Animals

Phylogeny of Animals

• Porifera (sponges) form a monophyletic group, meaning they consist of all descendants from one common ancestor.
• Cnidarians (hydras, sea jellies, and corals) branch off the tree before the origin of animals with bilateral symmetry (Bilateria).

Annelids and Arthropods

• Annelids (worms) and arthropods (spiders) are in separate clades (Lophotrochozoa and Ecdysozoa) despite both exhibiting segmentation.

Ctenophores and Chaetognatha

• The position of Ctenophores (sea walnuts) is currently debated.
• Whether Chaetognatha (marine worms) is a protostome or a deuterostome is unclear.

Phylogeny of Deuterostomes and Protostomes

• Deuterostomes have coeloms; protostomes are variable.
• Protostomes are divided into two clades: Lophotrochozoans (grow by gradual addition of mass) and Ecdysozoans (animals that molt, including arthropods).

Deuterostome Divisions

• Deuterostomes consist of fewer phyla and species than protostomes.
• They are more uniform in many ways, despite great differences in appearance.
• Deuterostomes include echinoderms (invertebrate marine animals) and chordates (mammals, fish, reptiles, and amphibians).

Kingdom Animalia (Metazoa)

• Kingdom Animalia is divided into two branches: Parazoa and Eumetazoa.
• Parazoa includes animals lacking tissues and organs, such as sponges.
• Eumetazoa includes animals with true tissues, organs, and organ systems.

Phylum Porifera (Sponges)

• Sponges are marine animals, with 26,000 species, and 150 freshwater species.
• Most sponges lack symmetry, have various growth forms, and some are capable of movement.

Sponge Characteristics

• Sponges have a "vaselike" shape with three functional layers of cells.
• They consist of a gelatinous noncellular layer (mesohyl) between two cell layers.
• Sponges are multicellular but lack organized tissue.

Learn about the evolutionary relationships between different animal groups, including Porifera, Eumetazoa, cnidarians, and Bilateria.