Sea Slugs and Nudibranchs

Sea Slugs

Arminid and Dendronotid Nudibranchs

Aeolid Nudibranchs

Dorid Nudibranchs

Slugs are snails without shells. Sea slugs are the two-thirds of the slugs that live underwater, about 4,000 species. These simple animals consist of little more than stomachs and their bodies which they use for crawling. They have gills to extract oxygen from the water and rows of serrated teeth with which to chew. Various types of sea slugs include: bubble snails, sea hares, headshield slugs, sap-sucking slugs, and nudibranchs.

Nudibranchs have large arrays of gills. Those may stick up from the body like the flowery tentacles of an anemone, or be arrayed around the outer edge of the body. They also have a pair of extensions near the bottom of the head. Those serve as fingers, sensitive to touch. They also have a pair of extensions on the top of the head, looking very similar to feathery horns and called rhinophores. These are very sensitive chemical sensors, which help nudibranchs find food by smell. Usually, the nudibranch can retract the gills and the rhinophores into their bodies to protect them. The main types of nudibranchs are the dorids, the aeolids, the dendronotids and the arminids. The dorids have the gills that stick out on top of their bodies, while the gills of the others are arrayed below. Aeolids have many thin extensions sticking out of their bodies; dendronotids have fewer, fatter extensions. Arminids look more like other sea slugs.

Many sea slugs feed upon coral. They store the toxic parts of the corals’s stinging cells in their bodies. That makes the sea slugs very unappetizing food for predators. The bright colors of the sea slugs advertise to potential predators that they are not very tasty.

One group of the aeolids is particularly interesting. These are the solar-powered nudibranchs. The name is applied to the two-dozen members of the genus Phyllodesmium in general, but also in particular to the species Phyllodesmium longicirrum. When these nudibranchs feed upon coral, they digest the animal parts of the coral, but they incorporate the living, green plant parts of the coral into their own bodies. They use the photosynthesis from the stolen plant parts to generate food for themselves.