Wednesday, October 30, 2019

This creeping pedal sea cucumber might just give you the creeps!

Eyes Under Puget Sound's Critter of the Month

Creeping pedal sea cucumber, Psolus chitonoides. Photo courtesy of Dave Cowles,
Move over, bats and spiders! With its blood-red tentacles and scaly body, the creeping pedal sea cucumber might just be the next creature to haunt your Halloween nightmares.

Jeepers Creepers

The creeping pedal sea cucumber, Psolus chitonoides, is shaped like a cucumber with a flattened bottom, but it is far from a vegetable you’d eat with hummus. It is closely related to sea stars, sea urchins, and sand dollars in the Phylum Echinodermata (meaning spiny-skinned). This “cuke’s” spiny skin is covered with rows of overlapping plates, kind of like an armadillo or its armored molluscan namesake: the chiton. It grows to a whopping 7 cm — a little bigger than a fun-size candy bar.

Keep calm and creep on

Psolus chitonoides with tube feet extended in rare moments of activity.
Left: Photo courtesy of Aaron Baldwin, Alaska Dept. of Fish and Game.
Right: Photo courtesy of Johanna Raupe,
Although its flat bottom side is covered in tube feet, this sea cucumber doesn’t do much creeping. It is mostly sedentary, preferring to attach its soft sole to smooth, vertical rock surfaces. It moves so little that other organisms often colonize the top of its body, camouflaging everything but the red feeding tentacles.

Don’t live in fear of a surprise encounter with this creepy cuke … It is generally found in deeper water (low intertidal zone to depths of about 240 meters) from Alaska to California. In 30 years of sampling in Puget Sound, we have only collected four of them; this is probably because our sampling occurs mostly in areas with soft sediments rather than rocks.

Dark Web

These creeping pedal sea cukes are in full feeding mode with
sticky red tentacles waving. Photo by Jim Nestler,
The ten tentacles of the creeping pedal sea cucumber form a cup-shaped mesh that resembles a red spider’s web. Just like a spider’s web, these tentacles ensnare food using a super sticky substance. Each tentacle tip has little pads called papillae that secrete an adhesive material used to capture particles of detritus (dead organic matter) from the water. The tentacles may even have some chemosensory abilities, moving vigorously when they sense food is near. The cucumber then stuffs each food-covered tentacle into its mouth (note that one of the individuals in the image to the right has a tentacle in its mouth).

Bad blood

Psolus chitonoides with its tentacles retracted. Photo courtesy
of Kevin Lee,
You might think that waving brightly colored tentacles around would be an invitation for predators to come snacking, but these cool cucumbers have a nasty trick in store for anyone looking for treats. Their tissues contain toxic chemicals called saponins that are poisonous to many organisms, including fish and mollusks.

This trick doesn’t always work. There are a few predators that aren’t affected by the chemicals, including the leather star, several species of sun stars, and the red rock crab. As a last-ditch effort to protect itself, the cucumber can completely retract its tentacles into its body. This leaves it looking like an unappetizing ball of orange armored plates. Now that’s what we call creepy, kooky, mysterious, and spooky!

By: Dany Burgess & Angela Eagleston, Environmental Assessment Program

Critter of the Month

Our benthic taxonomists, Dany and Angela, are scientists who identify and count the benthic (sediment-dwelling) organisms in our samples as part of our Marine Sediment Monitoring Program. We track the numbers and types of species we see in order to understand the health of Puget Sound and detect changes over time.

Dany and Angela share their discoveries by bringing us a Benthic Critter of the Month. These posts will give you a peek into the life of Puget Sound’s least-known inhabitants. We’ll share details on identification, habitat, life history, and the role each critter plays in the sediment community. Can't get enough benthos? See photos from our Eyes Under Puget Sound collection on Flickr.

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