Mangrove Mussel Shell, Myella guyanensis

Mangrove Mussel Shell, Mytella guyanensis. Shell collected from within the estuary of the Magdalena Bay complex, Baja California Sur, October 2018. Size: 3.5 cm (1.4 inches) x 2.1 cm (0.8 inches) x 0.6 cm (0.2 inches).  Collection, photographs and identification courtesy of Bob Hillis, Ivins, Utah.

Phylogeny: The Mangrove Mussel, Mytella guyanensis (Lamarck, 1819), is a bivalve mollusk that is a member of the Mytilidae Family of Mussel Shells. The genus Mytella is one of thirty-two genera in this family, and there are five species in this genus. They are also known as the Guiana Swamp Mussel and the Bicolor Mussel and in Mexico as Mejillón Fanguero de Guayana.

Description: The Mangrove Mussel shell has a trapezoidal  outline with a ventral margin that is straight to slightly concave. The posterior end of the shell is broadly rounded and the anterior end is short and slightly pointed. The beak is low and set back from the anterior end. The exterior is sculpted with very fine, concentric, lines. The exterior of shells are covered by a periostracum that is divided diagonally along the length of the shell with one half being dark green and the other half brown; the interior of the shell is white with purple tinges. Mangrove Mussels reach a maximum of 7.0 cm (2.8 inches) in length and 4.2 cm (1.7 inches) in height.

Habitat and Distribution: Mangrove Mussels are found attached to stones, buried in mud or muddy sand substrates in the intertidal zone, and are often associated with mangroves. They are a subtropical to tropical Eastern Pacific species and a tropical Western Atlantic species that in Mexican waters of the Pacific Ocean are found Magdalena Bay, Baja California Sur south to Guatemala. They are found throughout the Sea of Cortez. They are absent from Mexico’s east coast.

Ecology and Behavior:  Mangrove Mussels are suspension feeders that feed primarily on planktonic algae and suspended organic matter. They are gonochoric and reproduce sexually, through broadcast spawning, with internal fertilization. Mangrove Mussels are known to host the endoparasitic apicomplexan Nematopsis mytella. Their relationship with mangrove trees may be commensal or symbiotic, with the mussel receiving shade from the mangrove, possibly in exchange for providing nutrients to the mangrove through the mussel’s waste products.  Mangrove Mussels are edible and are harvested and farmed for commercial food production.  From a conservation perspective they have not been formally evaluated however they are fairly common with a relatively wide distribution and should be considered to be of Least Concern.

Synonyms: Modiola bicolor, Modiola brasiliensis, Modiola guayanensis, Modiola semifusca, Modiola subfuscata, Mytella bicolor, and Mytelus bicolor.