By: Dany Burgess & Angela Eagleston, Environmental Assessment Program
Meet the Eyes Under Puget Sound Critter of the Month, Priapulus caudatus, otherwise known as the cactus worm. January's critter is quite a beauty...
|Priapulus caudatus – Cactus Worm|
Cactus of the sea
|Priapulus caudatus. Photo courtesy of Atli Arnarson|
P. caudatus is actually giant in comparison to its microscopic relatives, reaching up to 15 centimeters in length! It prefers the cold water of high latitudes, and can be found from the shoreline all the way to the deep sea (about 7,500 meters.) Its favorite habitat is the soft silty mud of the sea floor, where it burrows hind-end-first by expanding and contracting the muscles in its body wall. It spends most of its time moving slowly through the sediment, reaching out with its proboscis to ensnare marine worms and any other slow-moving creatures it encounters.
Lifestyles of the weird and muddy
|Click to enlarge|
We are family!The family Priapulidae is a special group of cephalorhynchs that actually has more in common with shrimp or crabs than with worms. As they grow, priapulid adults and larvae shed their skin in a molting process called "ecdysis." The ecdysis process is similar to how crustaceans shed their outer shells.
Today there are only about 16 species of priapulids world-wide, but numerous priapulid fossils have been found dating back millions of years to the Cambrian period.
The animal’s anterior (head) end which contains the mouth.
The midsection, which has a ringed appearance and is covered with tiny bumps called papillae.
- Caudal appendage
A long feathery “tail”, which serves various functions depending on the species. Scientists speculate that the tail of P. caudatus may serve as a breathing organ.
Critter of the Month
|Close-up of caudal appendage|
In each issue we will highlight one of the Sound’s many fascinating invertebrates. We’ll share details on identification, habitat, life history, and the role this critter plays in the sediment community. Can't get enough benthos? See photos from our Eyes Under Puget Sound collection on Flickr. Look for the Critter of the Month on our blog.