Sea Mice of the Aphroditidae Family are segmented worms that along with earthworms belong to the Phylum Annelida. They perhaps are best described as a short stout worm with a fur coat. Their bodies are composed of ringed segments. Their body cavities are filled with coelemic fluid which, hydrostatically, provides rigidity to the body. Annelids have well-developed circulatory, digestive, and nervous systems.

Sea Mice are in the Class Polychaeta, which comes from the Greek words meaning “many bristles”. The bristles are chitinous setae, spines, or chaetae that assist the animal with movement, swimming, or anchoring. Most polychaete are free-living, but some live in tubes, burrows, or as parasites inside other animals.

Sea Mice are in the Order Phyllodocida, meaning that they are free-living. They have a protrusible proboscis that may have zero, one, or two sets of jaws. Their prostomium (first body segment) has one to five pairs of antennae and one to three pairs of eyes.

Sea Mice of the Aphroditidae Family are elliptical in outline with somewhat flattened bodies. Their bodies consist of around 40 segments, but these segments are difficult to see from the dorsal surface because they may be either partially or completely covered with iridescent threads or setae. 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 prostomium is globular with medium antenna, facial tubercle and if present 2 pairs of eyes on stalks. The thick layer of dorsal notosetae (felt-like hairs) gives them a mouse like appearance, hence the common name “sea mice.” Under their iridescent spines, Sea Mice may be bronze, brown, black, or yellow in color. Sea Mice reach up to 30 cm (12 inches) in length.

Sea Mice are found on and buried within mud and sand at depths between 2 m (6 feet) and 1,830 m (6,000 feet). They are difficult to locate as they are often covered with silt covered matted setae. They may be scavengers or predators and predatory Sea Mice feed on crustaceans, such as crabs and hermit crabs, or on other polychaetes, which may three times as long as themselves. In turn they are preyed upon by fish. Sea Mice reproduce sexually, with fertilization taking place externally.

Sea Mice are a common by-catch of shrimp trawlers. Those from the Atlantic and Mediterranean are well known and fairly well studied scientifically. In contrast, those from the Pacific have not. Some Sea Mouse species, in the north eastern Pacific, play host to a commensal bivalve, the Wrinkled Montaculid, Neaeromya rugifera. The setae of Sea Mice have applications in nanotechnology in that they function as nanowires. Spines from sea mice are known to cause long term damage to joints, bones and muscle tissue in humans. Handling of Sea Mice should be done with caution and medical attention should be sought if spines break off under the skin.

Sea Mice are found in tropical, temperate, and polar seas. At present there are approximately 105 species in Aphroditidae Family of which 4 are found in Mexican waters of the Atlantic in the Gulf of Mexico and at least 10 are found along Mexico’s Pacific Coast.