Invertebrate
Generic term of convenience for animals that do not have a vertebral column. The vast majority of Terragen animals, including such important phyla as the arthropods, annelids, nematodes, echinoderms and molluscs are invertebrate. Vertebrates account for only one part of one phylum. However, since these few species account for most of the largest and most active animals and gave rise to humans, and since most (though not all) Terragen-derived sophont clades are vertebrates, the distinction between vertebrate and invertebrate is useful in practice.

Strictly speaking the only biological species in the universe that are not invertebrates are those in the subphylum of chordates called the vertebrata. However the term 'invertebrate' is sometimes used informally in the description of xenobiota, especially on these gardenworlds containing a clade of organisms that do have something comparable to a vertebral column.
 
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Development Notes
Text by Stephen Inniss
after the original by M. Alan Kazlev
Initially published on 16 August 2012.