Chubby Simnia Mollusk, Simnia avena

Chubby Simnia Mollusk, Simnia avena. Underwater photographs taken in Zihuantanejo Bay, Guerrero. Photograph and identification of Ron Woheau, Zihuantanejo, January 2020.

Note:  You can find the Chubby Simnia Shell presented in our sister website Mexican Shells.org as Chubby Simnia Shell, Simnia avena.

Phylogeny: The Chubby Simnia Mollusk, Simnia avena (Sowerby, 1833), is a member of the Ovulidae Family of False Cowry Mollusks. 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 Mollusk 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: The Chubby Simnia Mollusk’s shell is shorter and stouter than most Simnias, but it is still an elongated, narrow, thin (to the extent that some shells are translucent), spindle-shaped shell. The exterior of the shell may be smooth or marked with very fine, spiral lines. 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 white, yellow, pink, red, or purple, often with darker spots. They also exhibit raised white papillae. The Chubby Simnia Mollusk reaches a maximum of 2.4 cm (0.9 inches) in length and 0.9 cm (0.3 inches) in height.

Habitat and Distribution: Chubby Simnia Mollusks are found attached to 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 Simnia Mollusks are ectoparasitic corallivores that feed on the polyps and flesh of their gorgonian hosts, including those in the genera Eugorgia, Muricea, Pacifigorgia, and Psammogorgia.

Predation: The predation of Chubby Simnia Mollusks is poorly studied and documented. Hawkfish of the Cirrhitidae Family are one of their primary predators.

Reproduction: Chubby Simnia Mollusks are gonochoric (male or female for life). They reproduce sexually, with internal fertilization. The eggs are laid in a mucus net, at the base of their host gorgonian. The eggs hatch into free-swimming planktonic veliger larvae before settling down onto a host coral to grow into adults.

Ecosystem Interactions: The engagement of Chubby Simnia Mollusks in any type of commensal, parasitic, or symbiotic relationship has not been formally documented. 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, Delonovolva aequalis aequalis, Neosimnia avena, Neosimnia avena avena, Neosimnia capitia, Neosimnia formicaria, Neosimnia spelta capitia, Ovula hordacea, Ovulum aequale, Ovulum avena, Ovulum lividum, Ovulum seminulum, Ovulum simile, Simnia aequalis, and Simnia rufa var. inflexa.