Discover 5 Types of Sea Animals With Shells (and Why They Have Them)

When you consider sea creatures that wear shells, you come to understand that a wide variety of marine life carry both their homes and defense against predators on their backs. Observing the animals that wear shells is fascinating, as is figuring out which animals are part of the same groups.

Fish include sea urchins and seahorses, while crustaceans include shrimp, barnacles, and crabs. Beautiful and fascinating creatures, both with and without shells, can be found in the underwater realm.

1) Echinoids

Sea creatures with hard shells known as echinoids are termed tests. They have what are known as tubercles on the test. In addition to having spines, the majority of echinoids are venomous.

Fish, crabs, octopuses, and other echinoids are among the predators of echinoids.

Sand Dollars

The majority of people have seen the beachside collections of white sand dollars. Because of this, people assumed that these creatures were white. after sand dollars are living, their exoskeleton is dark, but after they pass away, it becomes white. Sand dollars are dated by counting the rings surrounding their exoskeleton by scientists. The sand dollar creates a ring on its exoskeleton every year it lives, just like trees do.

A sand dollar’s holes serve as a release of pressure. Without holes, each wave would carry the animals away. The way sand dollars consume is through their spines. They are gregarious creatures who enjoy being with others.

Their defense mechanism against predators is their strong shells. These creatures are preyed upon by flounders, some eel species, and a different echinoid known as a huge pink sea star.

Sea Urchins

Sea urchin species number 950. Being omnivores, sea urchins seek cover from their shells. These marine creatures’ spines contain toxins and poisons that can harm humans. The most deadly sea urchin is the flowered variety.

A sea creature with shells of this kind can live up to 200 years. They don’t have any bones and most of them are edible.

2) Shellfish and Fish

Fish are aquatic animals that have bones, fins for breathing, and central spines. Although they are aquatic creatures as well, shellfish lack bones and spines. Rather, they possess a shell. It’s also intriguing that whereas shellfish only exist in saltwater, fish may live in both fresh and saltwater.

The hippocampal or sea horse (horse caterpillar)

These little fish are among the marine creatures that have shells. Their shells serve as a defense against scavengers. Despite their diminutive size, these animals have voracious appetites. Their favorite diets are brine shrimp and plankton, however food passes through their body fast, allowing them to acquire very little nutrition. Every day, 3,000 of the tiny shrimp can be consumed by one sea horse. They often consume thirty meals a day.

In addition to using their shells for protection, sea horses may conceal themselves from predators by changing their color like chameleons. When they are assaulted, they can defend themselves by using their tails.

Longhorn Blowfish or Longhorn Cowfish

The prey of longhorn cowfish is marine invertebrates. The fish exposes the invertebrates hiding in the sand by blasting water jets into the sand on the ocean floor. The longhorn blowfish protects itself by using its shell. In addition to being incredibly venomous, they can defend themselves with the horns on either side of their skulls.


The flattened spiral shell of an abalone serves as protection for the animal’s strong foot. An invertebrate that consumes algae is the abalone. Unlike most animals, abalone does not have red blood cells. Their blood has a greenish-blue hue. An abalone’s lack of blood clotting factors means that even a minor wound will cause the animal to bleed to death.

In many cuisines, abalone is regarded as a delicacy and is edible. Abalone and oysters both have the capacity to transform a pebble that irritates them into an invaluable pearl. An abalone can twist its shell until it pushes away a sea star that attacks it.


The majority of the 81 krill species are transparent. Because of the shape of their bodies and eyes, they resemble shrimp. Krill congregate and frequently form groups that are many miles deep and wide. A lot of marine species love them as food.

Up to 10,000 eggs can be laid at once by krill. The krill will hatch ten days after the eggs are deposited.

3) Mollusks


A chiton’s shell is flexible as opposed to rigid. Chitons use their shells to shield themselves when they sense danger. Chiton comes in about nine hundred to one thousand different species. They consume microscopic organisms like zooplankton and algae that inhabit the shallow waters of the ocean. Its only defense against predators is its shell.

A sequence of plates make up chiton shells. The individual plates are held in place by a girdle that encircles them. The abundance of these animals is higher in warmer ocean conditions. They reach a maximum length of two inches.


When fully grown, the nautilus measures six to eight inches. The nautilus uses its other senses, such as scent, to locate food and navigate despite having tiny eyes that let it to see in both light and dark environments. This animal’s shell contains a trap door that resembles a hood. To elude potential predators, the nautilus will close the trap door and totally immerse itself in its shell.

Neptilus: An octopus resembling a cephalopod. The nautilus possesses around ninety tentacles, whereas the octopus only has eight. Every year, females lay between 12 and 18 eggs, which take a year to develop and hatch. For a cephalopod, a nautilus’s lifespan of 12 to 15 years is lengthy.


The limpets are marine homebodies. They return to the same base and position after leaving it to dine at their preferred home base. They search for food actively when they are young, but as they get older, they start to settle down in one spot and wait for food to find them.

The limpet’s shell serves as both a dwelling place and a barrier against intruders. The female limpet is larger than the male, and they can reach lengths of two to three inches. Crustaceans can live up to sixteen years. Because it’s easier for them to move around underwater, they prefer to stay submerged.


The cowry uses its hard shells as a habitat and as barriers to keep predators out, just like other snails do. These water creatures that have shells consume carrion, seaweed, sponges, and algae. They’ll consume other gastropods as well. The cowries have a variety of colored shells, such as purple, white, and patterned ones. They can be found close to rocky sections of the ocean floor and have shells that resemble eggs.

Other sea snails are cowries’ primary predators. Cowrie shells are precious and their flesh delicious, thus humans also feed on them.


One of the most well-known water creatures with shells is the clam. Clams are edible and found in many different cuisines worldwide. The clam’s shell serves as a defensive device. The clam has the ability to seal its shell in response to danger, making it more difficult for predators to remove the live flesh.

Worldwide, there are 15,000 different species of clams. Clams burrow into the sand to evade being noticed. Evidence suggests that clams can live up to 500 years, yet they may have a brief lifespan. Clams can move along the beach or the ocean floor by pressing their one foot out of their shell.


Because the two halves of their shells are not the same form, scallops are unusual among sea animals. The scallop shell is flat in the upper portion and has a bowl-like shape in the lower part. They have 50–100 pairs of eyes, which they use to detect even the smallest changes in light. The scallop’s eyes seem blue.

They close their shells and shelter within when they feel danger. This bivalve mollusk’s only line of defense is its shell. Their shells open and close quickly, allowing them to swim. This aquatic creature often lives for twenty years. Although they can start reproducing at age two, they often wait until age four. Phytoplankton, algae, and other microbes are consumed by scallops.

4) Crustaceans


Among the water creatures with shells that most people are familiar with are crabs. The blue-shelled crab, hermit crab, king crab, and dungeness crab are among the 4,500 species of crabs. As part of their defense against predators, crabs have shells. In addition, the animals have strong pinschers that they can employ in combat or to elude a predator.

Some crab species are edible to humans, while others are poisonous. However, some crab species are consumed by humans. Decapods include crabs. In contrast to most crabs, which have eight legs and two claws, they have ten legs. Over time, crabs will sprout new appendages if they lose any. A wide range of algae, seaweed, worms, fish, and other items from their surroundings are consumed by crabs.


Oysters have a 20-year lifespan. An oyster’s shell, which is high in calcium, is used to improve garden soil. These animals have the ability to switch from being male to female. Up until the age of a year, the immature oysters are referred to as spats. Through their gills, they breathe.

An oyster’s ability to seal its shell and hide inside provides its only defense against predators. These creatures keep the water clean by filtering out marine algae. Up to 50 gallons of water can be filtered daily by a single oyster. For this species, algae is the only food source.


Sea creatures known as lobsters utilize their shells to shield themselves from potential predators. This marine creature can fend off predators or use its claws to escape them. They have two sizes of claws and various purposes for them. The biggest claw is used to seize objects and exert tremendous pressure. They rip or break their meal into bits with the smaller claw.

Lobsters have to grow new shells as they get bigger. We refer to this as molting. The lobster is susceptible to harm or death while it takes them months to produce a new shell.


A shrimp is a valuable food source of protein for ecosystems. In addition to being a food source for humans, shrimp are consumed by countless of aquatic species. These marine creatures resemble lobsters or crayfish in their pinschers. Shrimp are able to produce loud snapping sounds by snapping their pinschers.

Because they can swim quickly, shrimp can outwit some predators by outsmarting them in the water. Shrimp use their shells to shield themselves from predators, much like the majority of marine species. They consume both plant and animal materials because they are omnivores, and some larger shrimp also hunt tiny fish.

5) Reptiles

Cold-blooded creatures with fragile shells, reptiles lay eggs. Reptiles include turtles, crocodiles, alligators, and snakes. Reptile bodies are covered in hard scales that cover some of their body’s surface. A singular work of art is a reptile that resembles a sea creature with a shell.

Sea Turtles

Among the seven species of marine turtles are the leatherback. These marine creatures that have shells use them for protection, and the weight of their shells aids in their ability to swim against the powerful ocean currents. Among the 100 reptiles that live in ocean waters are sea turtles.

While female sea turtles climb onto sandy beaches to lay their eggs, males never leave the ocean. In the ocean, sea turtles live between 50 and 100 years. In captivity, they live longer because they are shielded from harm and contaminated environments.

Summary of Sea Animals That Have Shells

Sea Animal Type of Animal
Sea Urchins Echinoids
Sand Dollars Echinoids
Sea Horse Fish
Longhorn Blowfish Reef Fish
Pinto Abalone Shellfish
Krill Fish
Chiton Mollusks
Nautiluses Mollusks
Limpets Mollusks
Cowry Mollusks
Clam Molluscs
Scallops Mollusks
Crabs Crustacean
Oyster Crustacean
Lobsters Crustacean
Shrimp Crustacean
Sea Turtles Reptile

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