Question

the _ is a stiff rod of collagen that provides structural support and may develop into a vertebral column. cranium lophotrochozoa nematocyst notochord

Explanation:

• Cranium: It is the part of the skull that encloses the brain, not a rod - like structure for general structural support.
• Lophotrochozoa: This is a major group of animals (a super - phylum), not a structure.
• Nematocyst: These are stinging cells found in cnidarians (like jellyfish), not related to structural support in the context of a rod that can develop into a vertebral column.
• Notochord: It is a stiff rod (composed of collagen in some cases) that provides structural support in chordates. In vertebrates, it often gives rise to the vertebral column during development.

Answer:

notochord