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Life at the Bottom: Eight Aquatic Animals in the Benthic Zone

From schooling fishes swirling above to sleek sharks swimming overhead, you can always count on seeing an array of intriguing animals when you look up at the aquarium. However, with so many impressive creatures to discover at eye-level and above, you might miss all the interesting aquatic life at the bottom of our ocean, lakes or rivers.

Animals that roam the bottom of a body of water are called benthic, meaning they reside in the lowest section of water called the benthic zone. Benthic animals can live in freshwater or saltwater environments, and they come in all shapes and sizes. Some may crawl, some may float just over the bottom, and some may anchor themselves in place.

Here are some floor-dwelling animals at the aquarium that you should look for during your next visit!

A large red octopus sits in a rocky habitat with its tentacles curled around it.

Giant Pacific Octopus (Enteroctopus dolfleini)

One of our most popular benthic residents, the giant Pacific octopus, is an expert at navigating its home on the ocean floor. Octopuses are famous for their suction-cupped arms that allow them to skillfully move across the seafloor, but did you know that the giant Pacific octopus is capable of changing colors? Special cells, called chromatophores, contain pigments that the animal can manipulate to camouflage itself. Without a hard shell or other armor to defend themselves, octopuses must rely on this camouflage — blending in with rocky crevices or the sandy seafloor — to hide from predators.

A giant pacific octopus in its classic red coloring.
The arms and suckers of giant pacific octopus.

Giant Pacific Sea Cucumber (Apostichopus californicus)

The giant Pacific sea cucumber is the largest sea cucumber species at Shedd, capable of growing up to 2 feet, or over 23 inches. Like the octopus, it also moves using suction-cupped feet, although much slower. Sea cucumbers live in the shallow waters of tide pools, slowly searching for algae and microscopic plants to munch on. Adorned with bright red spikes to ward off predators, these odd creatures are sure to draw your eye.

Giant Pacific Sea Cucumber on coral

Giant Pink Star (Pisaster brevispinus)

On to the next giant! The giant pink star is exactly as its name suggests, with the ability to grow up to 28 inches in diameter. These constellational creatures are often found sitting on the sandy surface, which is a good place to find clams and other shellfish to eat. Although it may seem like sea stars are stationary, they move by pumping water through their bodies to propel them on their spindly tube feet (the size of a pin!) that help them move toward their prey.

A purple starfish clings to the glass with small pink feet.
A closeup of a starfish's toothy mouth surrounded by small pink feet.

Fiddler Ray (Trygonorrhina fasciata)

Marked with brown curving lines on its back, these roaming rays coast across the sand in search of food such as shellfish, crabs and worms. Because of its guitar-like shape, the fiddler ray may also be commonly known as the banjo shark. Their spines are lined with sharp, toothlike spikes, but don’t be fooled by their appearance. These rays aren’t poisonous and are harmless to divers. Although their eyes are on the top of their body, their small mouths face the floor to better help them eat creatures crawling on the sand.

Fiddler Ray swimming on sand

Honeycomb Moray (Gymnothorax favagineus)

The spots on this dynamic animal’s body resemble the inside of a beehive, hence its honeycomb name, but it has also earned the nicknames leopard eel and giraffe eel. This pattern provides camouflage for the eel to blend into the rocky areas near the ocean floor where it lives. While the honeycomb moray is a carnivorous predator, their constant biting motion is not for eating. Honeycomb morays must constantly open and close their mouths to pump water over the small gills on the sides of their bodies.

The honeycomb moray has the long, stocky body typical of moray eels, and is covered in an intricate pattern of dime-sized brown polygonal spots all over its body for a dizzying visual effect.

Japanese Giant Spider Crab (Macrocheira kaempferi)

This benthic invertebrate is the largest living crab in the world, with a possible total leg span of over 12 feet. Although its legs grow throughout its life, its carapace – the hard upper shell that protects the abdomen and head – stays the same size after the crab reaches maturity. Adult Japanese giant spider crabs rely on their intimidating size to ward off predators, but young crabs cannot do the same. Until they reach maturity, they will decorate their carapace with kelp or sponges to hide from any threats. Japanese giant spider crabs survive their cold, deep environment by taking in oxygen through gills instead of lungs. This equalizes the pressure of the deep sea so that the crab isn’t crushed.

Japanese Giant Spider Crab on rocks

Spotted Wobbegong Shark (Orectolobus maculatus)

While you can see blacktip reef sharks, sandbar sharks and other species swimming overhead in the shark habitat in Wild Reef, you may miss a benthic animal hidden in the sand. The spotted wobbegong lays motionless at the bottom of the water, almost invisible to predators as well as prey. Its dark brown body and beard-like appendages near its jaw are meant to hide features that would give away the presence of a shark to prey. Some researchers have theorized that the Australian Aboriginal name can be translated into “shaggy beard.” Wobbegongs never leave the ocean floor, so divers at Shedd deliver food to our resident wobbegongs twice a week.

A spotted wobbegong on the habitat floor at Shedd Aquarium
Spotted Wobbegong Shark swimming

West African Lungfish (Protopterus annectens)

The West African lungfish is what’s known as a “living fossil,” a prehistoric animal that has remained largely the same over the last 400 million years. As the name suggests, lungfish have two lungs like humans do, which means they can survive when the shallow waters of its habitat dry up. When the water rises again, lungfish can go four to five days without breathing air out of water. During a period called estivation, which is similar to hibernation, this species goes into a sleep-like state during the summer months. They burrow deep into the mud during this time, where they can remain for up to 4 years!

African Lungfish resting

- McKay Davis, Content Marketing Intern, Summer 2023