Stomphia: The Swimming Anemone

February 24, 2016

Jeremy Berg 
Department of Biology 
Lake Forest College 
Lake Forest, IL 60045

Introduction

Stomphia are sea anemones that are known for their swimming behavior. Many of these organisms can be found on the west coast of the United States, specifically in the Pacific Northwest region. They live in salt water at depths as deep as 80-100 meters, and their habitats consist of sandy gravel and shells of mollusks. Most Stomphia give off a bright orange coloration, can grow to roughly 6 cm in diameter, and have between 80-160 tiny tentacles. Stomphia feed on planktonic creatures as well as shrimp and other small crustaceans. Typically, sea anemones are known to be stationary organisms, which is what makes Stomphia so fascinating. The fact that they are able to perform a swimming behavior makes them unrivaled to other anemone species. So when do these anemones swim, and what does it look like?

Simple Mind, Complex

In most cases, Stomphia swim in the presence of predators. These predators include the leather sea star and the shaggy mouse nudibranch (sea slug), both found in the Pacific Northwest region. Stomphia’s initial reaction to these predators involves an attack with their tentacles and a lightning fast contraction, where they pull their tentacles within their entire body. Then, their bodies elongate and appear similar to an inverted umbrella in shape. This allows them to be carried off by a current, and the foot of the anemone swings back-and-forth like a pendulum. The anemones start pushing themselves through the water and swim, finding another area to inhabit. They are able to detect shells by landing on the surface of the ocean floor, and feeling around the perimeter with their tentacles and foot. Once they’ve found a place that is safe, Stomphia will move themselves upright and stay in place. It’s incredible how these marine animals have such intricate patterns of movement and are even able to escape from predators! This leads to the question: what is the neurological basis of this behavior?

As with all sea anemones, Stomphia are also invertebrates: they lack a vertebral column. It should also be noted that anemones do not contain a central nervous system, and instead have a “nerve net” that spans throughout their entire bodies. These nerve nets are dense and the neurons have fairly thick axons, allowing for fast conduction velocities up to 10 cm/s. This could be the reason that the anemones can react to stimuli remarkably fast. Little is known on the entire nervous system of Stomphia, and how they determine how to react to certain stimuli. This past summer, I worked with researchers Dr. William Frost and Dr. Christopher Brandon studying Stomphia, trying to understand if they have specialization within their nerve net that allows for these complex behaviors. We focused on muscular tissues called “mesenteries” that radially line the anemones’ bodies, and are responsible for the swimming behavior. We found what appeared to be smaller nerve nets within the muscle tissues that could explain how the anemones are able to perform such complex behaviors. Specifically, we saw different kinds of neural formations on the layers of muscle tissue, from linear bipolar neurons along the muscle fibers to clusters of multipolar neurons in the mesoglial spaces in between the muscle and epithelial tissue. However, further research is to be done to fully understand how these intricate nerve net- works possibly function together to create these interesting behaviors.

Conclusion

Stomphia and their swimming capabilities raise the question as to how organisms can function in such a complex way with a simple brain? Studying such an organism could not only explain the neurological basis of the anemone’s swimming, but also give us a picture as to what the evolution from invertebrates to vertebrates might have looked like, and how Stomphia could be a prime example of the beginning of that evolutionary transition. The swimming sea anemone is truly a remarkable creature that stands out from other anemone species. Further study of a species of anemone that can make decisions, detect specific stimuli, and perform unique behaviors without the use of a central nervous system can help further our understanding of the scientific universe.