The Arrow Dwarf Triton, Tritonoharpa lanceolata (Menke, 1828), is a very attractive, inch-long species found on the beaches of Sanibel and Captiva. It belongs in the family Cancellariidae, the same family as the more common, local Nutmeg. The Arrow Dwarf Triton occurs from North Carolina to Florida, the Gulf of Mexico and Caribbean. A very similar species, Leal's Dwarf Triton, Tritonoharpa leali Harasewych, Petit, & Verhecken, 1992 (named after yours truly!), is found off the coast of tropical Brazil.
The Arrow Dwarf Triton, Tritonoharpa lanceolata, from Sanibel.