Chubby Simnia, Simnia avena, Mollusk and Shell

Chubby Simnia, Simnia avena. Underwater photographs taken in Zihuatanejo Bay, Guerrero, November 2019. Photographs courtesy of Ron Woheau, Zihuatanejo.

Phylogeny: The Chubby Simnia, Simnia avena (Sowerby, 1833), is a member of the Ovulidae Family of False Cowry Mollusks and Shells. The Simnia Genus is one of forty-four genera in the Ovulidae Family, and there are thirteen species in the Simnia Genus. They are also known as the Gorgonian Spindle Shell and in Mexico as Ovúlido Avena. The genus name Simnia comes from the Greek word meaning “curl”. The species name avena is Latin for “oats”, referring to this shell’s resemblance to a head of grain.

Morphology: Chubby Simnia shells are shorter and stouter than most Simnias, but it is still an elongated, narrow, thin, spindle-shaped shell. The exterior of the shell may be smooth or marked with very fine, spiral lines, sometimes thin enough that it appears translucent. The aperture is very long and it grows wider at its lower end. The shells vary in color and can be brownish-lavender, lavender, orange, rose or white. The canal ends are usually a darker yellow or orange. The living animal varies in color to match its gorgonian host. Common colors include pink, purple, red, white, and yellow, with darker spots. They also exhibit raised papillae. Chubby Simnia shells reach a maximum of  2.4 cm (0.9 inches) in length.

Habitat and Distribution:  Chubby Simnias are found on gorgonians at depths between 5 m (15 feet) and 76 m (250 feet). They are a subtropical to tropical Eastern Pacific species that are found in all Mexican waters of the Pacific Ocean.

Diet: Chubby Simnias feed on the polyps and flesh of their gorgonian hosts, which include species in the Eugorgia, Muricea and Psammogorgia genera.

Predators: The predation of Chubby Simnias is poorly documented. Other species in the Ovulidae Family are preyed upon by crabs,  fish, gastropods and lobsters.

Reproduction: Chubby Simnias are gonochoric and reproduce sexually, with internal fertilization.  The females lay their eggs within mucus nets that are attached to, or at the base of, their host corals. The eggs hatch into planktonic larvae before settling on to their host gorgonian.

Ecosystem Interactions: The engagement of Chubby Simnias in any type of commensal, parasitic, or symbiotic relationship has not been formally documented.

Human Interactions: Chubby Simnias have very little impact on human activities. From a conservation perspective the Chubby Simnia has not been formally evaluated. However, they are fairly common with a relatively wide distribution and should be considered to be of Least Concern.

Synonyms: Delonovolva aequalis, Neosimnia avena, Neosimnia capitia, Neosimnia formicaria, Ovula aequale, Ovula avena, Ovula hordacea, Ovula lividum, Ovula simile, Simnia aequalis, and Simnia rufa.

Note:  The Chubby Simnia Shell is presented within a sister domain, Mexican-shells.org under Chubby Simnia Shell, Simnia avena.