[2] Least puffers are tetraodontids, meaning their teeth have fused into beaks with a median division that produces two plates in the upper and lower jaw.

[3] Tetraodontids can also be characterized by their lack of fin spines or ribs, and a tough skin that is often covered with small spinulous scales.

There is a ventrolateral row of black blotches, being irregular in size and arrangement, separating the dorsal and ventral colorations.

[5] S. parvus is most closely allied morphologically to S. maculatus, which is found in the Atlantic from Canada to northeastern Florida.

It is believed that prior to existence of the Florida peninsula, the progenitor species of S. parvus and S. maculatus was distributed along the southern coast of the United States.