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National Marine Week

This Marine Week we’re celebrating the rich diversity of marine species in our waters, highlighting the weirdest and most wonderful inhabitants of our coasts  so we can more deeply appreciate our marine ecosystem. Each evolved so specially to suite its particular and peculiar niche.

ocean creatures

The Sea Hare - Cute but deadly

First on our top 10 weirdest wonders for Cornwall’s Marine Week is the enigmatic Sea Hare. These intriguing ocean dwellers, classified as marine mollusks, are peculiar yet captivating members of underwater world around Cornwalls Coast. With their striking appearance, with sensory projections, curious frills and perplexing forms, they easily grab attention as one of the weirdest sea creatures found in our waters.

Despite their quirky looks, these sea slugs possess an endearing charm, with their large, expressive eyes and plump, cute bodies floating gracefully through the currents. However, don’t let their slow nature deceive you, as some species of Sea Hares secrete toxic substances when threatened, acting as a natural defense mechanism against potential predators. They primarily feed on algae, thus contributing to the control of algal blooms, supporting a healthy marine ecosystem and only come together for mating – forming rolling balls in shallow calm waters of competing lovers.

marine life

Stalked Jellyfish - Teeny Tiny

On of our favourites in the realm of marine life, the Stalked Jellyfish stand as peculiar wonders – mere 2cm in length, these tiny jellies lead a settled life, anchoring themselves to seaweed and rocks. Filtering microbial prey with flower-like projections, they thrive in the cold waters of the U.K. .

Cornwall is home to two rare types of these animals that live in the ocean upon living kelp: Calvadosia cruxmelitensis and Calvadosia campanulata. Elusive and well-camouflaged, spotting them remains a challenge, except for keen seekers of these extraordinary sea animals. These weird, cute, and strange sea creatures hold a unique place in the marine species, adding to our enchantment with our oceanic world.

weird sea creatures

Pipefish - Masters of Disguise

The captivating Pipefish species take center stage as mesmerizing marine animals.

These elongated sea creatures, akin to straightened seahorses, gracefully navigate the ocean currents. Their unique appearance, with slender bodies and charming features, adds to their allure yet puts them firmly in the realms of strange sea creatures.

Pipefish are very easy to mistake for a piece of seaweed or a twig with their dark olive, glistening bodies. They grow up to 15cm long but are only about a centimetre thick with a  upturned seahorse type snout and beautiful light green markings around the eyes and face.

Like their cousins the seahorse, but alike nearly every other animal, it is the male pipefish which carries and cares for the eggs – and they mate for life, making their separation when caught as bycatch akin to a death, as despite their survival after being thrown back they will never find their partner again so never breed. However unlike the seahorse who carries the eggs inside a pouch, the pipefish will carry them stuck to a small groove on the outside of their tummies.

marine mammals

Sea Urchins - Underwater hedhehog

Meet the fascinating Common Sea Urchin – a large, round creature adorned with short, robust spines. Its striking appearance ranges from pinkish-purple to red, green, or yellow. Inhabiting the seabed up to depths of 40m, these marine animals can even be spotted in rockpools during exceptionally low tides.

 As grazers, they indulge in a diverse diet of seaweeds, bryozoans, barnacles, and anything else they come across. Belonging to the echinoderm family, alongside starfish, sea cucumbers, and brittlestars, their scientific name “Echinus” draws inspiration from the Greek word for hedgehog, undoubtedly evident in their spiky appearance.

marine animals

Thornback Ray - Boneless

Thornback Rays are intriguing  marine animals. They belong to the shark family and possess no bones, like all sharks. With their unique shape resembling a flat diamond, these sea animals gracefully navigate the waters, using their oversized fins to glide through.

Aptly named for the thorns on their back, Thornbacks primarily indulge in a diet of crustaceans and fish. These cute and weird sea creatures have fascinating behaviors, burying themselves in the sand during daylight hours, only to emerge at sunset for their hunting endeavors. Targeting crabs and ambushing other smaller marine creatures. Witnessing these rare and strange sea creatures was a delightful experience during a recent dive in the Carrick Roads – however not a very photogenic one as they love to bury down into the mud and sandy beds!

cute sea creatures

Ctenophores - Little Living Lightshows

Amidst the wonders of marine life, comb jellies shine as enchanting and mysterious creatures, exemplifying the marvels that await in the depths of the ocean. These tiny set of ocean creatures dazzle with their shimmering rainbow-coloured fibres called cilia, reflecting the sun’s rays. Although commonly named jellyfish, they belong to their unique Ctenophore family of marine animals. In Cornwall, the most distinctive feature is the comb-like structures on their bodies, primarily used for swimming. Comb jellies employ a fascinating movement method using cilia, the same as microbes, making them the largest organisms to do so. As they gracefully glide, their cilia create a rainbow effect, transforming them into otherworldly creatures.

The Nuda type, lacking tentacles, resembles a swimming mouth, capable of “biting off” prey. Surprisingly, their ancestors, dating back 500 million years, had hard skeletons, evident in their rare fossils.

Despite their beauty, comb jellies can become a menace when unintentionally transported in ships’ bilges. One invasive species drastically impacted the Black Sea, devouring fish larvae and adult fish food. Fortunately, another invasive species helped balance the ecosystem, mitigating the threat posed by these boneless killers to the Black Sea. Who says two wrongs cant make a right.

The weirdness and wonder of the marine world wouldn’t be complete without Ctenophores aka Comb Jellyfish, the laser-shows of the sea.

sea animals

Starfish - Regenerate limbs

The spiny starfish (Marthasterias glacialis) is a captivating marine creature with fascinating features. This echinoderm boasts five arms covered in sharp, spiky spines, which serve as a defense mechanism against predators. Surprisingly, they have the ability to regenerate lost limbs, making them exceptional survivors. These starfish possess tiny suction-cup-like structures, called tube feet, which aid in locomotion and capturing prey. While they predominantly feed on mollusks, they have been known to eat other starfish too! Found in the rocky intertidal zones of the UK, spiny starfish play a crucial role in maintaining the ecological balance of their marine habitats.

strange sea creatures

Cuckoo Wrasse - colour changing

Cuckoo Wrasse are a colourful and playful fish found in the waters of Cornwall, and the wider Atlantic Ocean and the Mediterranean Sea. What makes them truly remarkable is their ability to change color during mating displays or when they feel threatened, showcasing a vibrant range of bright orange and blue hues. These charismatic fish have a peculiar behavior of adopting the color patterns of the opposite sex to confuse rivals and predators. As quirky members of marine life, Cuckoo Wrasse add a touch of fascination to the underwater world, captivating divers and snorkelers with their chameleon-like antics.

animals that live in the ocean

Cuttlefish - Creative Camouflage

Cuttlefish are incredibly fascinating creatures, known for their exceptional camouflage abilities. They can change the color, pattern, and texture of their skin to blend seamlessly into their surroundings, making them expert escape artists from potential predators. Additionally, they can rapidly change their skin color through specialized cells called chromatophores, not only for camouflage but also for communication and mating displays.

Surprisingly, cuttlefish possess three hearts, with two pumping blood through the gills and a third circulating oxygenated blood to the rest of the body. They also have the largest brain-to-body ratio among invertebrates, displaying remarkable intelligence and problem-solving skills.

Their distinctive W-shaped pupils provide a 360-degree field of vision and superior depth perception. Cuttlefish use a unique mode of transportation, jet propulsion, by expelling water through a siphon, propelling them backward at impressive speeds. 

As exceptional hunters, cuttlefish use their tentacles to capture prey and their beak to crush and consume it. When threatened, they deploy an ink defense mechanism, releasing a cloud of ink to create a smokescreen, confusing predators and allowing them to escape. Despite their intelligence, cuttlefish have relatively short lifespans, typically living for only one to two years.

Furthermore, cuttlefish are social beings, engaging in complex behaviors, including mating rituals and communication through changes in body patterns. Their charm and captivating nature continue to intrigue scientists and enthusiasts, revealing the incredible wonders of the ocean.

sea animal list


Sand Dollars are captivating marine creatures that enthrall both beachgoers and marine enthusiasts with their unique characteristics and intriguing life cycle. These round, flat echinoderms are related to sea urchins and starfish, featuring intricate petal-like markings on their rigid skeletons, resembling small, white coins. While often found washed up on sandy shores, they spend most of their lives partially buried in the seabed, moving about using tiny spines and tube feet.

Their name “sand dollar” derives from their appearance, resembling old silver dollar coins when washed ashore, and they hold cultural significance as tokens of good luck or currency from the sea in some cultures. As herbivores, sand dollars feed on algae and organic particles, capturing them with specialized cilia on their spines and creating small depressions in the sand to trap and consume their food.

Exhibiting pentaradial symmetry like other echinoderms, sand dollars can be divided into five equal parts. When threatened, they have a remarkable defense mechanism of burrowing into the sand, leaving only their upper surface exposed to evade predators. Fossilized remains of sand dollars date back millions of years with an identical form, providing valuable insights into ancient marine ecosystems.

Their life cycle involves female sand dollars releasing eggs into the water, fertilized externally by male sand dollars. The larvae undergo several stages before developing into the familiar flat, circular shape. While their exact lifespan varies based on species and environmental factors, they typically live for several years, making their short lives even more precious.

Despite their abundance in some areas, sand dollars face threats from pollution, habitat destruction, and climate change, emphasizing the importance of preserving their coastal ecosystems. Sand dollars continue to evoke wonder and curiosity, serving as a reminder of the hidden marvels beneath the ocean’s surface.

Read about The Sharks of Cornwall or Man of War in Cornwall next.

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