Vidler’s Simnia Shell, Simnia arcuata

Vidler’s Simnia, Simnia arcuata. An exceptional portfolio of underwater photographs taken in Zihuantanejo Bay, Guerrero, March 2022, courtesy of Ron Woheau, Zihuantanejo.

Vidler’s Simnia Shell, Simnia arcuata (Reeve, 1865), is a species of sea snail that is a member of the Ovulidae Family of cowry allies or false cowries and ovulids that is known in Mexico as ovúliudo aruata.

Vidler’s Simnia Shell has an elongated oval profile with their mantle completely covering their shell. The mantle has color patterns that closely resemble the color pattern of the host species, a phenomenon known as “alimentary homochromy” whereby they obtain their color via feeding on the host. This affords them with a high level of camouflage that helps them avoid predation. They reach a maximum of 2.6 cm (1.0 inches) in length.

Vidler’s Simnia is a benthic species that is found intertidally under rocks, in crevices or on rock walls at depths up to 18 m (60 feet). They live on and feed on coral polyps to which they anchor by a long and narrow foot and referred to as extoparasites. Reproduction is sexual. Their shells have smooth shiny shells that are narrowly ovate, arched, with a very long aperture with thickened lips and are white in color. Vidler’s Simnia is poorly studied and very little has been documented about their behavioral patterns and biology.

In Mexican waters their range is not well documented, but they are believed to be found within the Sea of Cortez and along the coast of the mainland south to Guatemala.

From a conservation perspective the Vidler’s Simnia has not been formally evaluated.

Synonyms: Neosimnia arcuate, Neosimnia quaylei, Neosimnia tryianthina, Neosimnia vidleri, Ovulum arcuatum, Ovulum neglectum, Pseudocyphoma gibbulum and Spiculata advena.