Mexican Dancer, Elysia diomeda

Mexican Dancer, Elysia diomedea. Sea slug collected at Km 17, El Tule, Baja California Sur, November 2011. Length: 2.6 cm 1.0 inch).

Mexican Dancer, Elysia diomedea. Underwater photographs taken in Zihuatanejo Bay, Guerrero, February 2020 and January 2022. Photograph and identification courtesy of Maude Jette, Dive Zihuatanejo, www.Divezihuatanejo.com.

. Mexican Dancer, Elysia diomedia. Underwater photographs taken in Zihuatanejo Bay, Guerrero, January and February 2023. Underwater photographs taken in Zihuatanejo Bay, Guerrero, in February 2022. Photographs courtesy of Ron Woheau, Zihuatanejo.

Phylogeny: The Mexican Dancer, Elysia diomedia (Bergh, 1894), is a member of the Plakobranchidae Family of Solar Sea Slugs.  The genus Elysia is one of four genera in this family, and there are one hundred three species in this genus. This species is also known as Diomede’s Sapsucker and in Mexico as babosa marina, bailarina Mexicana, and danzarina Mexicana. They are a sister species of the Lettuce Sea Slug, Elysia cirspata, found in the Caribbean, which were believed to be one and the same species until the Panama land bridge closed and they evolved into separate species.

Morphology: The Mexican Dancer has an oval outline with a relatively high profile. They  have frilled parapodial lobes on their dorsal surface. Mexican Dancers vary in color depending on the location, depth and light conditions but are generally green to greenish-brown in color. They have broken white lines running parallel to the long axis of the body, small blue spots scattered over the dorsum and the inner walls of the parapodium, and a border of black spots. The fringes of the frilled parapodium may be orange, pink, white or yellow. The rhinophores are marked with black and yellow to white bands. Mexican Dancers reach a maximum of 7.5 cm (3.0 inches) in length.

Habitat and Distribution: The Mexican Dancer is found on and under rocks and within reefs from the intertidal zone to depths up to 23 m (75 feet). In Mexican waters the Mexican Dancer is a resident of the Pacific and it is the most common opisthobranch on the West Coast of Mexico and Central America. They are common throughout the Sea of Cortez and range south along the coastline of the mainland south to Guatemala.

Diet: Mexican Dancers feed on algae, by piercing and sucking out the insides of algae cells. They are also “Solar Sea Slugs”, retaining living chloroplasts in their tissue, which continuously photosynthesize and provide the sea slug with sugars for its own nutrition. This process of incorporating chloroplasts into their cells is known as kleptoplasty. This requires that Mexican Dancers remain in relatively shallow water to have sufficient sunlight for photosynthesis to occur.

Predators: Mexican Dancers are eaten by a sea slug known as the Enigmatic Navanax, Navanax aenigmaticus. 

Reproduction:  Mexican Dancers are simultaneous hermaphrodites (having both male and female reproductive organs). Reproduction is sexual with internal fertilization. The fertilized eggs are laid, by the thousands, in a flat spiral  ribbon. The eggs hatch into veliger larva and remain in a planktonic state for some time before metamorphosing into their benthic adult state.

Ecosystem Interactions:  Mexican Dancers have an endosymbiotic relationship with the algae that they incorporate into their body cells through kleptoplasty. There are no other documented parasitic, commensal or symbiotic relationships.

Human Interactions: Mexican Dancers have a very limited direct impact on human activities. From a conservation perspective they have not been formally evaluated however they are fairly common with a relatively wide distribution and should be consider to be of Least Concern.

Synonyms:  Tridachia diomedia and Tridachiella diomedia.