Final answer:
True, A slug is indeed not a vertebrate because it lacks a backbone, making it an invertebrate like snails and other gastropods.
Step-by-step explanation:
A slug is not a vertebrate because it has no backbone. This statement is true. Slugs, like snails, are gastropods which are a group of molluscs, and they are invertebrates. Invertebrates are animals without a vertebral column, as opposed to vertebrates which include mammals, birds, reptiles, amphibians, and fish, all of which have a backbone. It is worth noting that all vertebrates are also chordates, which at some stage in their development have a notochord. However, not all chordates are vertebrates; some invertebrates in the chordate phylum do not develop into vertebrates. For instance, humans are chordates because of our vertebral column among other characteristics, rather than the presence of a tail.