Mexican Skirt Dancer, Pseudoceros mexicanus

Mexican Skirt Dancer, Pseudoceros mexicanus. Flatworm collected at KM 17, El Tule Baja California Sur, January 2012. Size: 6.3 cm (2.5 inches). Identification courtesy of Bob Hillis, Ivins, Utah.

Mexican Skirt Dancer, Pseudoceros mexicanus. Underwater photographs taken in Zihuantanejo Bay, Guerrero, March 2019. Photographs courtesy of Ron Woheau, Zihuantanejo.

Phylogeny: The Mexican Skirt Dancer, Pseudoceros mexicanus (Hyman, 1953), is a member of the Pseudocerotidae Family of Flatworms. The genus Pseudoceros is one of nine genera in this family, and it is comprised of one hundred thirty-nine species. In Mexico they are known as gusano plano bailarin Mexicano. The Mexican Skirt Dancer derives its common name from its graceful undulating swimming movements that resemble a dancer’s skirt.

Morphology: The Mexican Skirt Dancer has an elongated oval profile with strongly ruffled lateral margins. They are black, brown or reddish-purple in color and are covered with numerous white spots that do not extend to the margin. The margin is marked by a light orange to reddish orange band.  They reach a maximum of 10.0 cm (3.9 inches) in length.

Habitat and Distribution: The Mexican Skirt Dancer is found on and under rocks within tidal pools and intertidally at depths up to 18 m (59 feet). They are fairly strong swimmers. In Mexican waters the Mexican Skirt Dancer is a resident of the Pacific Ocean that is found along both coasts of the Baja Peninsula, and south along the coast to the central mainland.

Diet: Information specific to the diet of Mexican Skirt Dancers has not been documented. Other flatworms in this genus are predatory carnivores eating  ascidians (sea squirts) and sponges.

Predators:  Predation of Mexican Skirt Dancers has not been documented. Other flatworms in this genus are eaten by fish and crabs.

Reproduction:  Mexican Skirt Dancers are simultaneous hermaphrodites. They reproduce sexually through hypodermic insemination ( stabbing the penis through the body tissue). The eggs are laid in masses on the bottom substrate. The eggs hatch into Muller’s larva, which eventually metamorphose into adult organisms.

Ecosystem Interactions:  Information specific to the relationships of Mexican Skirt Dancers with other species has not been documented.

Human Interactions:  Mexican Skirt Dancers are attractive and entertaining to watch and they are utilized by  the aquarium trade. Indiscriminate collecting has had a negative effect on local populations. Otherwise, they have no direct impact on human activities. From a conservation perspective they have not been formally evaluated however they are fairly common with a wide distribution and should be consider to be of Least Concern.