What type of animal is a shell-less gastropod?
Gastropod shell along, solid surfaces such as rocks, or other shells. Most gastropod shells are spirally coiled. The majority (over 90%)<ref>[https://www.ncbi.nlm.nih.gov/pubmed/16217668 Schilthuizen M. & Davison A. (2005). "The convoluted evolution of snail chirality". "Naturwissenschaften" 92(11): 504–515. Gastropod shell The gastropod shell is part of the body of a gastropod or snail, a kind of mollusc. The shell is an exoskeleton, which protects from predators, mechanical damage, and dehydration, but also serves for muscle attachment and calcium storage. Some gastropods appear shell-less (slugs) but may have a remnant within the mantle, or the shell is reduced such that the body cannot be retracted
Gastropod shell study of gastropods, and other molluscs in general, is malacology. Shell morphology terms vary by species group. An excellent source for terminology of the gastropod shell is "How to Know the Eastern Land Snails" by John B. Burch now freely available at the Hathi Trust Digital Library. The gastropod shell has three major layers secreted by the mantle. The calcareous central layer, tracum, is typically made of calcium carbonate precipitated into an organic matrix known as conchiolin. The outermost layer is the periostracum which is resistant to abrasion and provides most shell coloration. The body of the snail contacts the