Have you ever been snorkeling and seen something loaf shaped on the bottom and wondered what on earth that was? Well, most likely you were looking at a Sea Cucumber – which is an animal, despite its similarity to something else entirely.
What are sea cucumbers?
Sea Cucumbers are animals classified in the same Phylum (Echinodermata) as sea stars – they have tube feet powered by a water-vascular system that they use to walk along the bottom of the ocean.
Despite their somewhat spiny appearance, their bodies are actually very soft and malleable. The flexible nature of their body is due to microscopic spicules in their skin instead of large plates or ossicles found in other echinoderms.
They move along the seafloor by contracting and relaxing two different sets of muscles; a layer of circular muscles and five bands of long, lengthwise muscles. This flexibility is advantageous for avoiding predation by squeezing into tiny cracks and crevases.
So how do sea cucumbers eat?
Although sea cucumbers have a somewhat undifferentiated looking body, with no clear way to tell the mouth end from the anus, their anatomy is more complex that you might think.
Notice in the diagram below, on the left there are feather-like tentacles surrounding the mouth. These tentacles are actually modified tube feet that can be extended or contracted. Sea cucumbers use these tentacles to grab and pull food towards their mouth.
Sea Cucumbers are detrivores – this means that they eat the detritus (anything that falls to the bottom of the ocean floor) by scooping up sediment in their tentacles and bringing it to their mouth. Anything indigestible is excreted out their anus. This is very similar to earthworms.
In this video clip you can see a sea cucumber slowly extending its tentacles and feeling around for something to eat.
Sources:
- Sea Cucumber. https://en.wikipedia.org/wiki/Sea_cucumber
- Echinoderm Species. Flower Garden Banks National Marine Sanctuary. Url: https://flowergarden.noaa.gov/about/echinodermlist.html#:~:text=Echinoderm%20is%20the%20common%20name,symmetry%20in%20their%20body%20shapes.
- Sea Cucumbers. Wildlife Federation. Url: https://www.nwf.org/Educational-Resources/Wildlife-Guide/Invertebrates/Sea-Cucumbers#:~:text=Sea%20cucumbers%20are%20part%20of,used%20for%20locomotion%20and%20feeding.
- Introduction to Phylum Echinodermata. Exploring our fluid earth. University of Hawai’i. Url: https://manoa.hawaii.edu/exploringourfluidearth/biological/invertebrates/phylum-echinodermata
Erica Lauer Vose 