Sea Slugs

In the post I wrote about Nudibranchs I explained that they are also called “Sea Slugs”, which defines a group of marine invertebrates that resemble terrestrial slugs, including Echinoderms, Platyhelminthes and mollusks such as Nudibranchs or snails.

These marine invertebrates can be used as a good example to understand why common names are often shared by animals from very different taxonomic groups.   The common name may give you an idea of the kind of shape, size or coloration of the animal, but they are not useful for a precise taxonomical identification because the name is not accurate nor specific. Snorkeling Panama

Other species that could be called “Sea Slug” in Bocas del Toro are the different sea cucumber species like the Five-Toothed Sea Cucumber (Actinopygia agassizii) or species of flat worms like the one called Thysanozoon raphaeli.

Sea cucumbers are, as Nudibranchs, benthic organisms, meaning, they are found on the ocean floor or over reefs, or mangrove roots.  They look like a terrestrial slug because of their soft body, their shape and their movements. Sea Cucumbers are part of the Phylum Echinodermata.

Panama Snorkeling

Thysanozoon raphaeli can be found swimming in a salt water column at mangrove lagoons near Bastimentos Island.  In the pictures you can observe how similar it is to the Nudibranch, and to a terrestrial slug (even though almost all Nudibranchs are benthic organism and this flat worm is always found “swimming”).  T.raphaeli belongs to the phylum Platyhelminthes also known as “flat worms”.

Snorkeling in Bocas del Toro

The Flamingo Tong (Cyphoma gibbosum) belongs to the Class Gasteropoda as does the Nudibranchs but it is in the subclass Prosobranchia, which means that is considered a Snail. The mantle in this species is covered completely by the reduced shell it has, so it makes it seem like a slug.

As you can see in the pictures, they look alike and that is the reason they share a common name, but that common name could never be accurate if we were trying to identify a single specie, not even to define the taxonomic group that a particular species belongs to.