Chapter: Invertebrates

Synapomorphies

What makes an invertebrate an invertebrate?

• Simply put, all invertebrates lack a backbone (vertebrae).

• Despite so, the phylogenetic concept of synapomorphy CANNOT be applied here as this is NOT a formal taxonomic group. It is merely a naming convention created out of convenience to describe all animals outside of the Vertebrata subphylum. 

• Because urochordates and cephalachordates also lack a backbone (despite being grouped together with vertebrates under the Chordata phylum), they are referred to as "invertebrate chordates".