About Agathistoma viridulum (Gmelin, 1791)
This species is the marine gastropod Agathistoma viridulum, originally described by Gmelin in 1791. The shell of this species measures between 13 mm and 30 mm in size. It is a solid, umbilicate shell with a conoidal shape. Shell color ranges from whitish-grayish to greenish, with radiate crimson or rich brown stripes on the upper surface, and either spots or radiate stripes of the same color on the lower surface. The short spire is rather obtuse. The shell has six convex whorls, surrounded by spiral lirae that are more or less beaded on the upper surface; the interstices between these lirae have fine minute spiral striae. There are approximately six lirae on the penultimate whorl. Below the periphery, the lirae are finer, more closely spaced, and nearly smooth. The body whorl is obtusely angulate or rounded at the periphery. The base of the shell is rather flattened, somewhat concave around the umbilicus, and is typically eroded in front of the aperture. The aperture is oblique. The outer lip is beveled to an acute edge, which is usually margined with green and is either sulcated or crenulated, with the furrows matching the lirae on the shell's outer surface. The pearly throat is also more or less sulcate. The arcuate columella is expanded above into a bright green callus that partly surrounds the umbilicus; the base of the columella is green, and bears one tubercular tooth followed by several smaller teeth. The basal margin is smooth or denticulate on the inner side. The umbilicus is wide and deep, and is white or greenish inside. This species is distributed in the Caribbean Sea off the coasts of Colombia, Costa Rica, Panama, and Venezuela, and also occurs in the Atlantic Ocean off Brazil.
