Sea Anemone Facts & Worksheets

The sea anemone is a sessile, water-dwelling marine predator named after the equally colorful Anemone genus of terrestrial flowers. They are stinging polyps attached to seafloor rocks or coral reefs. They resemble corals, jellyfish, tube-dwelling anemones, and hydra.

See the fact file below for more information on the Sea Anemone, or you can download our 31-page Sea Anemone worksheet pack to utilize within the classroom or home environment.

Key Facts & Information

OVERVIEW

• Sea anemones are soft-bodied tubular animals with a flat base that holds them to the surface and a central mouth on top surrounded by iconic tentacles which they use to catch their prey.

• They are sessile, water-dwelling, filter-feeding predatory animals with a wide range of colors and can be found across the world’s oceans. These species range in size from 0.5 inches to 6 feet.
• Each species has a distinct appearance. The most common resemble underwater flowers with thick, tubular stems.
• The color of the sea anemone is very ornate, and they are named after terrestrial flowers.
• They have a radially symmetric appearance and numerous tentacles.
• The colorful anemones belong to the Actiniaria order of the Anthozoa class. They are members of the phylum Cnidaria, which includes jellyfish and corals, and other animals that use specialized stinging cells to capture prey.

ANATOMY

• A sea anemone has the typical polyp structure, with a tiny sac attached to the bottom by an adhesive pedal disc or foot. It has a cylindrical body that ends in an oral disc. 
• A cavity in the center serves as both the mouth and the anus, and it is surrounded by tentacles contained in cnidocytes—cells used for both protection and prey capture.
• Nematocysts are the stinging elements found in cnidocytes. There is a small vesicle filled with a toxic compound known as actinoporins, an inner filament, and an external sensory hair. 
• When an organism comes into contact with a nematocyst, a cell explosion occurs, releasing a harpoon-like structure that attaches to the organism and injects venom.
• The venom contains neurotoxins that aid in prey capture by paralyzing it. Thus, the prey is subsequently moved into the mouth by the tentacles for digestion inside the gastrovascular cavity. When mixed with water, the toxins also serve as a defense mechanism against potential predators.
• The anemones’ muscles and nerves are simple. Microfilaments in the outer layer (epidermis) and the inner layer (gastrodermis) of cells form contractile fibers.
• Anemones’ internal anatomy has a gastrovascular cavity. As they are invertebrates, they have no bones and lack eyes and ears. Their tubular bodies have a single opening on the outside that serves as a mouth and anus. 

DISTRIBUTION AND HABITAT

• Anemones are found in all marine habitats around the world. They occur in various temperatures, from cold North Pacific waters to warm Caribbean waters. 
• More than 1,000 species of sea anemone have been discovered living at different depths, from shallow intertidal waters to depths of 3,000 meters.
• They typically lead benthic lives. Other species may be pelagic, meaning they float across the ocean, while others may burrow into soft sediments and anchor themselves with a bulbous base.
• Like all deep-water creatures, these sea anemones have adapted to survive in the low-light and low-food-source waters of the deep ocean. On the other hand, most sea anemones live much closer to the ocean’s surface and provide vital habitat for a variety of fish, eels, stingrays, and sharks.

ECOLOGY

• Many sea anemones have a vital symbiotic relationship with certain single-celled green algae living in the animals’ gastrodermal cells. These algae could be zooxanthellae, zoochlorellae, or a combination. These are typically concentrated at the tips of their tentacles and in other upward-facing areas of the anemone’s body.
• The sea anemone benefits from the algae’s photosynthesis products, namely oxygen and food in the form of glycerol, glucose, and alanine; the algae, in turn, are assured of consistent sunlight exposure, which the anemones actively maintain.
• A sea anemone and a clownfish can form a symbiotic relationship. Because a protective mucus covers the clownfish, it inserts itself into the anemone and lives peacefully amid the stinging tentacles.
• This relationship benefits the clownfish because it is protected by the anemone, and the anemone benefits because it receives food scraps from the clownfish.

DIET AND NUTRITION

• The majority of anemones are predatory. Sea anemones get their nutrition from living things, despite their harmless appearance and lack of teeth or claws. They stun and grasp their prey with their tentacles’ stinging cells, often paralyzing it with toxins before moving it to their oral cavity for digestion.
• Various crustaceans, such as crabs and shrimp-like organisms, are common anemone prey. The predatory sea anemone may also prey on small fish, zooplankton, and mollusks such as mussels.
• When a fish or crab approaches too closely, the sea anemone shoots out a stinging tentacle and injects the prey. The paralyzing venom works quickly to paralyze the unfortunate victim, who is then drawn into the anemone’s clutches and digested.
• The anemone can harvest some of the energy produced by photosynthetic organisms in the form of glycerol, glucose, and alanine, which is an essential supplement to their diet.

PREDATORS

• Sea anemones, with their stinging tentacles, appear to be an unlikely meal choice for most ocean-dwelling creatures. However, many species of fish, sea stars, snails, and even turtles have been known to feed on anemones opportunistically.
• The predators have a variety of unique methods of snacking on the anemones.
• Several types of snails and sea slugs feed on anemones, eating both the body and the tentacles by advancing on the anemone several times despite being stung and then biting their prey.
• Sea stars, such as the leather star, hunt anemones with their keen sense of smell. The star will wrap itself around the anemone.
• Anemone tentacles are eaten by a variety of fish, including butterfly fish and mosshead sculpins, with anemones contributing to at least 40% of the mosshead sculpin’s diet. Rather than swallowing the anemone whole, these fish feed by pecking at and biting at its tentacles.
• The loggerhead turtle can be found in every ocean except the Arctic and eats anemones as one of its main food sources. They eat them by biting and quickly crushing their prey with their powerful jaws.

REPRODUCTION

• Sea anemones have separate sexes. Some species are hermaphrodites as well. Sexual and asexual are both possible reproductions.
• In sexual reproduction, the male releases sperm, which stimulates the female to release eggs, followed by fertilization. The eggs or sperm are discharged through the mouth. The fertilized egg develops immediately into a planula larva, settles onto the seafloor, and grows into a single anemone.
• Asexual reproduction happens through budding, fragmentation, transverse binary fission (splitting into halves), or pedal laceration. Pedal laceration occurs when pieces of the pedal disc break off and regenerate as small anemones.

THREATS

• All marine life faces serious risks from both climate change and plastic waste. These sea creatures may be in danger when the ocean warms as a result of the climate change issue. Anemones can expel their symbiotic algae when they are exposed to warmer water, a process known as bleaching.
• Sea anemones are capable of ingesting the tiny plastic fibers found in saltwater, and it appears that stressed, bleached sea anemones are more at risk as the plastic remains. 
• The anemones that were exposed to pollutants also had significantly fewer stinging cells (also known as cnidocytes), which are used by them as a defense mechanism and to catch prey.

OTHER INTERESTING FACTS

• If their environment becomes unlivable, sea anemones float away and “swim” by flexing their bodies along the ocean floor.
• Although most sea anemones are poisonous only to their prey, some species are highly toxic to humans. Some are even potentially fatal to humans due to their toxicity.
• Sea anemones usually live in large “armies” close to one another. To protect their territories, some anemone colonies fight other groups. “Scouts” look for available space to claim. If another group’s anemone gets too close, the “warriors” slap it with special tentacles that leave patches of stinging cells stuck to the intruder.

Sea Anemone Worksheets

This fantastic bundle includes everything you need to know about the Sea Anemone across 31 in-depth pages. These ready-to-use worksheets are perfect for teaching kids about the Sea Anemone, a water-dwelling marine predator named after an equally colorful terrestrial flower.

Complete List of Included Worksheets

Below is a list of all the worksheets included in this document.

• Sea Anemone Facts 
• K-W-L Chart
• The Anemone’s Profile
• True Colors
• Anemone’s Anatomy
• Time to Hunt!
• My Reproduction
• The Invertebrates
• Stronger Together
• Protect the Anemones
• Amazing Anemones

Frequently Asked Questions

What is an anemone?

An anemone is a type of marine invertebrate that belongs to the phylum Cnidaria. They have a cylindrical body with a ring of tentacles surrounding the mouth.

What do anemones eat?

Anemones primarily feed on small marine animals such as plankton, fish, and crustaceans. They capture prey with their venomous tentacles.

Where do anemones live?

Anemones are found in a wide range of marine habitats, including rocky shores, coral reefs, and sandy bottoms.

How do anemones reproduce?

Anemones reproduce both sexually and asexually, depending on the species. Some anemones reproduce by releasing eggs and sperm into the water, while others reproduce through fragmentation or budding.

Are anemones poisonous?

Yes, anemones have venomous cells called cnidocytes in their tentacles that they use to capture prey and defend themselves from predators. Some anemones are harmful to humans and can cause skin irritation or allergic reactions.

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