Japonica Sea Mouse, Aphrodita japonica

Japonica Sea Mouse, Aphrodita japonica. Sea mouse provided by the commercial fishermen of the greater Los Cabos area, Baja California Sur, October 2009. Size: 13 cm (5.1 inches) x 5.7 cm (2.2 inches). Productive discussions with Dr. Richard Brusca, Tucson, Arizona, noted and this identification should be considered tentative.

Phylogeny:  The Japonica Sea Mouse, Aphrodita japonica (Marenzeller, 1979) is a polychaete worm that is a member of the Aphroditidae Family of Sea Mice. The genus Aphrodita is one of seven in this family, and there are forty-four species in this genus. This species is also known as the Japonica Aphrodite Worm and in Mexico as gusano afrodita japonica. They obtain their common name from a thick layer of dorsal felt that gives them a mouse-like appearance. There are eight family members found in the northern portion of the Sea of Cortez and four in the southern portion.

Note:  The Japonica Sea Mouse, due to lack of scientific study of the Sea Mice of the Pacific, is difficult to identify conclusively. Identifications are based on the relationship of the elytra to the notosetae, the palps, the length of the prostromium, the number of body segments and their color. This identification is based on the coppery or gold color of the animal.

Morphology:  The Japonica Sea Mouse is best described as a short worm with a fir coat. Their bodies are short, broad, and segmented. The body cavity is filled with coelemic fluid, which gives them rigidity. They are elliptical in outline and taper at both ends.  Japonica Sea Mice are either partially or completely covered with iridescent threads or setae that emerge from the dorsal surface. Their back bears 15 pairs of raised scales. The 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. They are composed of millions of submicroscopic crystals that reflect and filter the faint light at ocean depths. The prostomium is globular with medium antenna, facial tubercle and  2 pairs of eyes on stalks.  The elytra (flattened plates) are smooth and without barbs. Their palps are 4 to 7 times longer than the prostomium. The median antennae are at least as long as the prostomium. Their body has 38 to 43 segments. They reach a maximum length of of 18 cm (7.1 inches).

Habitat and Distribution:   The Japonica Sea Mouse resides buried head first within mud and sand substrate, at depths between 14 m (46 feet) and 1,170 m (3,838 feet). This species ranges from British Colombia to Ecuador. In Mexican waters the Japonica Sea Mouse is a resident of the entire Pacific coast,  but has a limited distribution within the Gulf of California- from Bahía de los Ángeles, Baja California to the greater Los Cabos area, Baja California Sur.

Diet:  Japonica Sea Mice are detritivores and predators that consume suspended organic matter, crustaceans,  and other polychaetes.

Predators:  Japonica Sea Mice are preyed upon by various fishes.

Reproduction:  Japonica Sea Mice reproduce sexually, with external fertilization. They are poorly studied and very little is known about their behavioral patterns.

Ecosystem Interactions: There are no documented symbiotic, commensal, or parasitic relationships for the Japonica Sea Mice.

Human Interactions:  From a conservation perspective the Japonica Sea Mouse has not been formally evaluated. They are often caught as a by-catch by deep-water shrimp trawlers and are of limited interest to most. The Japonica Sea Mouse is of scientific interest because they are one of the few marine species, in addition to Sea Cucumbers, that utilize anal respiration.

Synonyms: Aphrodita cryptomarginata, Aphrodita leioseta, Aphrodite japonica, and Aphroditella japonica.