1. The outermost layer of a spiral shell, often thin and organic.

1. The small, initial coil of a spiral shell formed by a young mollusk.

2. Gently curved ridges radiating from the apex to the base of a spiral shell.

3. A small, horny plate that some spiral shell mollusks use to close the aperture.

4. A genus of sea snails with long, tightly-coiled spiral shells.

5. A single revolution or turn of a spiral shell.

6. A group of mollusks that includes octopuses, squids, and nautiluses with spiral shells.

7. A compartment or section within a spiral shell.

8. The pointed, spiraled extension of some spiral shell mollusks.

9. A protective structure containing eggs, often formed by some spiral shell mollusks.

10. A type of invertebrate animal that often has a spiral shell.

11. A small, low conical marine mollusk with a cap-shaped spiral shell.

12. A tall, slender structure formed by the coiling of a spiral shell.

13. A thin wall dividing chambers within a spiral shell.