From red mud to pizza: Meet the sea stars in the Gulf of Maine

I have had many visitors gasp when they see the deepwater red mud stars and pizza stars in my tanks. They exclaim they can’t be from the Gulf of Maine, “All the animals here are dull in color.” Not so.

The deepest part of the Gulf of Maine harbors some of the most beautiful, colorful animals. Sea stars, in particular, are incredibly diverse animals.

Sea stars, or starfish as some people call them, are echinoderms like sea urchins, sand dollars and sea cucumbers. These animals are radially symmetrical (round and equal on all sides), have spiny skin, and a mouth on the ventral (bottom) side. They also have tube feet along each ray (arm) along the oral groove (a groove leading from the tip of their ray to their mouth). These tube feet are basically long tubes with a suction cup on the end. They are used in locomotion and in moving food down the oral groove to the mouth.

All echinoderms have a water vascular system, which means they use seawater instead of blood. Sea stars, despite not having blood or a heart, have an intricate system of radial canals that pass water throughout their body to all the cells. This is where oxygen is exchanged, and waste is discharged. The water comes in through their sieve plate, located off-center on their dorsal (top) side.

The sieve plate acts as a filter, keeping dirt and debris from entering their body. When water flows through the radial canals in their body, their tube feet fill up with water. The pumping causes suction to the end of the tube feet. Despite not having a brain or heart, they can move without expending any extra energy. If only we could manage the same thing!

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Deepwater stars have the extra stress of living in an environment that is extremely cold, dark, and with added pressure. Amazingly, due to their intricate water vascular system and simple anatomy, they do not have to worry about changes in pressure. They are automatically keeping their internal pressure the same as the external pressure. They don’t suffer from the bends like more complex animals such as fish and other vertebrates.

Red mud stars, sometimes called horse stars, are unlike common sea stars found in tidepools throughout the Northeast. This sea star is not an animal of the intertidal zone and will never be spotted in a tide pool or along the coastline. They live between 150 and 400 feet below the ocean surface, where they inhabit the muddy areas of the ocean floor. Not much is known about their habits in the deep ocean, but they can be found in deep water off Massachusetts up to the polar regions of Canada.

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Mud stars have a hard, thick, almost-leather-like skin separated by small plates that allow them to move slowly. The upper surface of this star is bright orange and covered with rounded white “spines.” Like all stars, this star has a mouth on the underside (ventral side) along with two rows of suction discs (tube feet) that run up each of the arms (rays). These suction discs allow them to move slowly through the mud as they search for food. The underside is whitish, with plates running along each arm (ray).

The pizza star is truly unique. Its "pizza star" name, sometimes called badge or cushion stars, was coined by Dr. Chuck Walker of UNH. This deep water star could really get your taste buds rolling! The top or dorsal side appears to be a juicy slice of cheese pizza. Unlike most sea stars, this star has a layer of “slimy” skin above its spiny dermis.

The skin is comprised of small papillae, which is the animal’s respiratory organ. They “breathe” through their skin! In the Gulf of Maine, these animals can be found from 33 feet to 1000 feet down, depending on the temperature on the ocean floor. They are extremely sensitive to pollutants and changes in temperature or salinity. They appear to be predators of other soft-bodied animals such as sea anemones and other invertebrates. They also will eat small organisms within their habitat. The underside has rows of tube feet and a mouth in the center. The underside is also covered with a “slimy” layer. Food is pushed along the oral grooves into the mouth from the tips of their rays, thus allowing them to eat even small detritus (particles) in the water.

As with most sea stars, digestion is usually by extruding their stomach through their mouth and digesting things outside their body.

Commercial fishermen and lobstermen haul these animals in with their traps and nets throughout the Gulf of Maine, yet most of us will never see one of these deepwater treasures.

Ellen Goethel is a marine biologist and the owner of Explore the Ocean World at 367 Ocean Blvd. at Hampton Beach.