What fundamental internal structure confirms a caecilian's identity as a vertebrate, unlike an earthworm?

Answer

A vertebral column, skull, and ribs

As tetrapods, caecilians possess a rigid internal bony skeleton including a skull, vertebral column, and ribs, which is absent in worms.

What fundamental internal structure confirms a caecilian's identity as a vertebrate, unlike an earthworm?

#Videos

Caecilian facts: they're amphibians! | Animal Fact Files - YouTube

taxonomyamphibianwormtetrapodCaecilian