The Beautiful Naked Gills

I have a friend who will argue that sea slugs are the world's most beautiful animals.  I am not so sure that the word "slug" is one that you mind immediately links with "beauty," but we are not talking about your everyday garden slime.  The sea slugs, or nudibranchs (for "naked gill"), consist of several thousand species, the vast majority of which inhabit the tropical marine habitats.  These animals are close relatives of the snails.  They are hermaphrodites, as each individual possesses fully functioning male and female reproductive systems.  Sea slugs exhibit a wide array of color patterns and behaviors, and some of their characteristics are unique among Kingdom Animalia.

Glaucus atlanticus

One species, Glaucus atlanticus, lives in the water column.  It floats upside down at the sea surface and feeds upon jellies and their close relatives.  They are able to ingest and incorporate the stinging cells of the jellies without trigging the cells and then use them for their own defense.

Flabellina iodinea

The Spanish shawl (Flabellina iodinea) can actually be found in local waters off California.  These sea slugs consume tissue from animals such as hydroids and anemones.  In doing so, they ingest stinging cells without causing them to discharge.  The Spanish shawl can then later use the stinging cells of its prey for its own defense.

Placida sp.

In Biology, one learns that plants, algae and some bacteria are able to synthesis their own organic compounds utilizing energy from sunlight.  That is, such organisms are photosynthetic.  Plants and algae have special structures inside of their cells called chloroplasts where the process of photosynthesis occurs.  In the same breath, teachers will explain that animals do not have this ability and must consume organic molecules from other organisms.  While all of this is true, a few of the sea slugs do present an unusual case.  Species from the genus Placida feed on algae.  They are able to ingest the chloroplasts from the algal cells, avoid destroying them, and then store them.  The chloroplasts then continue to function in the body of the sea slug, making these sea slugs the only animals on the plant to be "solar powered."

Some sea slugs are predators that have no trouble ingesting other members of their group.  Navanax is a large predatory slug that occurs off southern California.  It is no uncommon to catch it in the act of ingesting another nudibranch.  The video here shows yet another predatory species in action.

The variety in shape and color pattern is immense, so it actually is a bit difficult to ignore the thousands of beautiful species that we have failed to highlight here.  The mission is more to reveal their existence.  If these have caught your eye, you can explore the group further by reading through the short articles at Sea Slug Forum.  That's right; there is a forum dedicated to these creatures.