Mexican Aphrodite Worm, Aphrodita mexicana

Mexican Aphrodite Worm, Aphrodita mexicana. Sea mouse provided by the commercial fishermen of the greater Los Cabos area, Baja California Sur, October 2009. Size: 5.5 cm (2.2 inches) x 2.4 cm (0.9 inches). Productive discussions with Dr. Richard Brusca, Tucson, Arizona, noted and this identification should be considered tentative.

Phylogeny:  The Mexican Aphrodite Worm, Aphrodita mexicana (Kudenov, 1975),  is a member of the Aphroditidae family of Sea Mice. The genus Aphrodita is one of  seven genera in this family, and there are forty-four species in this genus. They are also known as  the Gulf Sea Mouse and in Mexico as Gusano Afrodita Mexicano. Due to the lack of scientific study of Sea Mice from the Pacific it is difficult to conclusively identify Mexican Aphrodite Worms, and very little is known of their range or ecology.

Morphology:  The Sea Mouse has perhaps been best described as a short stout worm in a fur coat. Mexican Aphrodite Worms are, like their cousins the earth worms, segmented worms. Their bodies are composed of around 46 ringed segments. Their body cavities are filled with coelemic fluid which, hydrostatically, provides rigidity to the body. They have well-developed circulatory, digestive, and nervous systems. Mexican Aphrodite Worms are elliptical in outline, and flattened in profile. They are polychaetes, coming from the Greek word meaning “Many Bristles”. Their dorsal surface is covered in fine silky bristles, which assist the animal with movement, swimming, or anchoring. Heavier, iridescent, golden, spines outline the lateral margins. These spines are poisonous and arranged laterally and when threatened they can be raised and fixed in position. Normally these setae have a red sheen, believed to warm off predators, but in light can flush green and blue. The setae are composed of millions of submicroscopic crystals that reflect and filter the faint light at ocean depths. Their backs bear 15 pairs of raised scales. The thick layer of dorsal notosetae (felt-like hairs) gives them a mouse like appearance, hence the common name “sea mice.” They are usually covered in fine silt, making recognition difficult. Mexican Aphrodite Worms reach a maximum of 12.5 cm (4.8 inches) in length.

Habitat and Distribution: Mexican Aphrodite Worms are found on, or buried in, mud. They live at depths between 46 m (150 feet) and 122 m (400 feet). They are an Eastern Pacific species. Sources differ on the geographic range of this species within Mexican waters. Some sources say they are endemic to the entire Gulf of California, some sources extend this range south to  Guatemala, and some limit their range to the central and southern Gulf of California. They are absent from the west coast of the Baja Peninsula.

Diet:  Mexican Aphrodite Worms are a poorly studied species. There is no documentation regarding their diet. Other species in this family feed as either predators or scavengers. Predatory Sea Mice feed on crustaceans, such as crabs and hermit crabs, or on other polychaetes.

Predators: Mexican Aphrodite Worms are preyed upon by fish.

Reproduction: Mexican Aphrodite Worms are gonochoric (male or female for life). Reproduction is sexual, with external fertilization. The females produce a pheromone attracting and signaling the males to shed sperm which in turn stimulates females to shed eggs. The gametes are spawned through a rupture in the body wall.  The  fertilized eggs hatch into trocophore larvae. These larvae later metamorphose into the juvenile stage, and then into the adult stage.

Ecosystem Interactions:  Mexican Aphrodite Worms are a poorly studied and understood species. There is no documentation of commensal, parasitic, or symbiotic relationships. The Wrinkled Montacutid, Neaeromya rugifera, a bivalve has a commensal relationship with sea mice of this genus in more northern waters, where they attach themselves to the Sea Mouse’s ventral side. Similar behavior has not been documented with this species.

Human Interactions: Mexican Aphrodite Worms are often caught as by-catch by deep water shrimp trawlers. There is insufficient data to determine how this impacts their populations. Spines from sea mice, which penetrate human skin, are known to cause long term damage to joints, bones and muscle tissue. Sea Mice should be handled with caution and seek medical attention if spines break off under your skin. From a conservation perspective the Mexican Aphrodite Worm has not been formally evaluated however they are fairly common with a relatively wide distribution and should be consider to be of Least Concern.

Synonyms:  None.