The two features that define animals and their clades include their adult body plans and their patterns of embryological development.

According to the fossil records, the first animals evolved before the Cambrian Explosion, which happened 600 million years ago. The fossils that were found comprised of eggs, embryos, and body parts. Some indirect evidence from the past which is in the form of trace fossils like tracks and burrows were also discovered.

According to the cladogram of chordates, the true bones evolved first. This resulted in the evolution of ray-finned fishes. Then, it was followed by the formation of lungs, which is a feature seen in lungfishes.

The illustration below shows a new invertebrate under the Phylum Arthropoda. It has a bilateral symmetry body plan that consists of a mouth, compound eyes, a cephalothorax, an abdomen, sensory organs, antennae, and appendages. These features fit right in the characteristics of arthropods in the cladogram of invertebrates.

The illustration below shows a new invertebrate under the Phylum Arthropoda. It has a bilateral symmetry body plan that consists of a mouth, compound eyes, a cephalothorax, an abdomen, sensory organs, antennae, and appendages. These features fit right in the characteristics of arthropods in the cladogram of invertebrates. (Click to see illustration)

Corals have a mutualistic relationship with the photosynthetic algae, which live in the coral’s tissues. The algae conduct photosynthesis and provide the oxygen and nutrients that are required by the corals in order to survive and build their calcium carbonate skeleton. In turn, the corals protect the algae and provide them shelter for their growth.