Ontogenetic allometric analyses can provide novel insights into aspects of evolution, ecology, and conservation. For example, a recent study found marine fish exhibit hyperallometric scaling of reproductive output in relation to body size. Accordingly, to sustain fish populations the largest size class of fish should be protected. The present study exploits a model sea urchin to explore allometry to evaluate skeletal defense and feeding efficiency (Aristotle’s lantern). Lytechinus variegatus were sampled from St. Joseph Bay, Florida. A range of different sized juvenile to adult individuals were measured and then dissected into skeletal components. Skeletal defense was evaluated by examining whole-body wet mass versus primary spine density (#), length (mm), breakage-strength (N), and Mg-calcite levels (% – high mg skeletons are harder). Feeding efficiency was inferred from the relationship between whole body wet mass versus lantern dry wt and mg-calcite content. Results indicate that L. variegatus displays isometric scaling between body size and various elements of skeletal defense and feeding efficiency. Hyperallometric scaling is also seen between body size and lantern size. Intriguingly, many components of spine defense against predation displayed a non-significant, body size independent relationship indicating juveniles have invest heavily in spine defenses at a young age. Lantern mass displayed a strong hyperallometric relationship with test diameter reflecting the importance of elevating feeding efficiency with increasing age. In the broadest sense, the present study validates that allometric scaling is valuable as a tool to evaluate aspects of defense and feeding efficiency in marine invertebrates.