Marine animals characteristics, types, examples

Abraham McLaughlin
Marine animals characteristics, types, examples

The Marine animals They present an important diversity, reaching around 230,000 species in all the oceans of the planet. This figure refers to the species identified so far, estimating that the real number may be close to one million..

Of these, the most characteristic group are fish with about 16,000 species, while there are about 80 species of cetaceans. Most animal species are concentrated in zooplankton, being very small animals.

Some marine animals

However, in general terms the marine biodiversity is much lower than the terrestrial one, mainly due to the greater uniformity of the environment. Another limiting factor is the scarcity of some determining resources such as electricity..

Article index

  • 1 What are marine animals?
  • 2 Characteristics of marine animals
    • 2.1 Breathing
    • 2.2 Salt concentration
    • 2.3 Temperature
  • 3 Types of marine animals
    • 3.1 Vertebrates
    • 3.2 Invertebrates
  • 4 Examples of marine animals
    • 4.1 Blue whale
    • 4.2 Dolphins
    • 4.3 Orca (Orcinus orca)
    • 4.4 Narwhal (Monodon monoceros)
    • 4.5 Seals (Phocidae family)
    • 4.6 Sea lions and lions (family Otariidae)
    • 4.7 Sea snakes (subfamily Hydrophiinae)
    • 4.8 Sea turtle (family Cheloniidae)
    • 4.9 Whale shark (Rhincodon typus)
    • 4.10 White shark (Carcharodon carcharias)
    • 4.11 Tuna (Thunnus spp.)
    • 4.12 Marlin or marlin (family Istiophoridae)
    • 4.13 Puffer fish (family Tetraodontidae)
    • 4.14 Seahorse (genus Hippocampus)
    • 4.15 Moray (family Muraenidae)
    • 4.16 Coelacanth (Latimeria chalumnae)
    • 4.17 Octopus (order Octopoda)
    • 4.18 Squid (superorder Decapodiformes)
    • 4.19 Sperm whale (Physeter macrocephalus)
    • 4.20 Beluga (Delphinapterus leucas)
    • 4.21 Crabs (infraorder Brachyura)
    • 4.22 Lobsters and lobsters (families Nephropidae and Palinuridae)
    • 4.23 Krill (order Euphausiacea)
    • 4.24 Mussel (family Mytilidae)
    • 4.25 Coral polyp (Anthozoa class)
    • 4.26 Jellyfish (Scyphozoa class)
    • 4.27 Sea anemone (order Actiniaria)
    • 4.28 Sea urchin (Echinoidea class)
    • 4.29 Starfish (Asteroidea class)
    • 4.30 Sea spiders or brittle stars (class Ophiuroidea)
    • 4.31 Sponge (phylum Porifera)
    • 4.32 Red-lipped batfish (Ogcocephalus darwini)
    • 4.33 Eel shark (Chlamydoselachus anguineus)
    • 4.34 Drop fish (Psychrolutes micropores)
  • 5 References

What are marine animals?

Whales, sharks and other marine animals

The essential characteristic of marine animals is the fact that they require a medium composed of water with a high content of salts to live. This requires a series of adaptations that allow them to inhabit said environment, depending on the type of animal..

In the case of fish and marine invertebrates, they have a respiratory system that enables them to absorb dissolved oxygen in the water. However, there are lungfish that can also take advantage of atmospheric oxygen.

For their part, marine mammals, provided only with lungs, require regular ascent to the surface to breathe air. In addition, aquatic animals must withstand varying concentrations of salts in the environment and the temperature of seawater..

The group of marine animals includes both vertebrate and invertebrate animals, that is, with or without backbones and skulls. The first group includes fish, reptiles, mammals and seabirds. While invertebrates constitute the largest group, including marine worms, sponges, echinoderms, crustaceans and mollusks.

Characteristics of marine animals



Since marine animals live in an aquatic environment, they face the problem of breathing vital oxygen for their existence. In this environment, oxygen is dissolved in water, so a different respiratory system is required than in the terrestrial environment..

Marine animals use diffusion respiration or gill respiration. Diffusion is used by sponges and many other groups, consisting of absorbing oxygen through the skin or cell membranes. Brachial respiration is used by fish.

For their part, animals that evolved from land to sea, such as cetaceans (whales, dolphins), maintain lung respiration. This forces them to periodically surface to breathe.

Salt concentration

The different species have adapted to variations in the concentration of salts in the oceans. For example, coral polyps do not survive in very salty waters, while coelacanth fish accumulate urea in their blood to balance the concentration of salts in the water..

In this way, they balance the concentration of the exterior, taking into account that the cells lose water (they become dehydrated), in media with a high concentration of salts..


Orcas in the Arctic

The marine temperature varies between the surface that receives solar energy and the deep waters, also varying with latitude. Thus, the water is warmer at low latitudes near the equator and very cold at the poles..

For its part, the waters are warmer on the surface and very cold at great depths. Therefore, the different species adapt to each condition, just as there are some capable of passing from one environment to another..

For example, there are marine animals in the Arctic that have antifreeze proteins in their blood, like some fish. While cetaceans face the problem with high body temperatures and thick layers of fat under the skin to keep warm..

Types of marine animals

For simplicity, marine animals can be separated into two large groups, a natural one called vertebrates and the other called invertebrates, which includes 95% of marine animals.


Whale skeleton

In the group of vertebrates are all those marine animals that have a skull and backbone. These include fish, marine reptiles, and marine mammals, as well as seabirds..

Among the fish are bony (tuna, hake), cartilaginous (sharks, rays) and jawless fish (lamprey, witch fish). While reptiles include sea turtles and sea snakes.

Vertebrate marine mammals are represented by cetaceans (whales, dolphins, orcas), sirens (manatees), fócidos (seals) and otáridos (lions and sea lions). Regarding seabirds, although they do not live strictly in seawater, they are considered marine animals because they require this medium to feed..



It groups together all the other marine animals that are not interpreted as vertebrates because they do not have an articulated internal skeleton, neither bone (bones), nor cartilage. This includes arthropods, such as crustaceans, mollusks (oysters, octopuses, squid), echinoderms (starfish and sea urchins), and porifers (sponges).

Likewise, this group is made up of cnidarians, such as jellyfish and corals, flatworms or flatworms such as sea slugs, and annelids or ringed worms..

Examples of marine animals

Blue whale

Blue whale

The blue whale (Balaenoptera musculus) is the largest existing animal on the planet. Its main food is microscopic crustaceans, similar to tiny shrimp called krill.


Bottle nose dolphin

There are about 30 species of marine dolphins, some small like the Heaviside dolphin (Cephalorhynchus heavisidii), other larger ones, such as the bottlenose dolphin (Tursiops truncatus). Others larger to the point that they are called whales, such as pilot whales (Globicephala), but they are big dolphins.

Orca (Orcinus orca)

Killer whale

Although they are associated with whales, the orca also belongs to the marine dolphin family. In fact, it is the largest dolphin in size reaching up to 8 meters in length with a dorsal fin of up to 1.8 meters..

Its body is black on the back and white on the belly, with an elliptical white spot on each side of the head. The killer whale, like all dolphin species, are highly intelligent animals and move through the oceans using echolocation.

This means that they emit sounds that bounce off objects and capture through a specialized organ, being able to establish sizes and distances.

Narwhal (Monodon monoceros)

Illustration of two narwhals in 3D

It is another very peculiar toothed whale due to a tusk that grows as if it were a long and straight frontal horn of up to 3 meters, which corresponds to a spiral-shaped canine tooth. The narwhal inhabits the cold waters of the Arctic, growing to about 5 meters and is white mottled with dark brown.

Seals (Phocidae family)

Seal (Monanchus sp.). Source: N3kt0n / CC BY-SA (

With the exception of the freshwater Baikal seal, seals are a family of marine mammals, almost entirely from a temperate and cold climate. Only monk seals inhabit tropical and subtropical climates, including the Mediterranean monk seal (Monanchus monanchus) and those of the genus Neomonachus in HawaiiNeomonachus schauinslandi) and the Caribbean (Neomonachus tropicalis).

These animals are more efficient swimmers than their relatives the walruses and sea lions, but more clumsy on land. On the other hand, they lack ears, hence they are also called earless seals..

Sea lions and lions (family Otariidae)

Sea lion of the species Otaria flavescens

These are known as eared seals, since although very small, they have external ears unlike the so-called true seals. They constitute a group of 15 species belonging to 7 different genera, being animals that spend more time on land than seals.

Among these species is the Guadalupe sea lion (Arctocephalus townsendi), which lives mainly on the island of Guadalupe, Mexico.

Sea snakes (subfamily Hydrophiinae)

Sea snake

There are more than 69 species of sea snakes belonging to this subfamily of the Elapidae family. This is the same family of land snakes called coral snakes, which produce deadly venom.

Like their terrestrial relatives, most of these snakes have showy ring colorations. In addition, they breathe through lungs, so they must come to the surface to breathe.

Sea turtle (family Cheloniidae)

Green turtle (Chelonia mydas). Source: Brocken Inaglory / CC BY-SA (

There are 6 species of sea turtles, all belonging to this family, characterized by more or less rounded flat shells. As well as paddle-shaped legs to facilitate swimming and the inability to retract the head into the shell.

Among them is the green turtle (Chelonia mydas) and the hawksbill turtle (Eretmochelys imbricata), both in danger of extinction. The other species are the loggerhead turtle (Caretta caretta), the olive ridley (Lepidochelys olivacea) and the Australian sea turtle (Natator depressus), endemic to Australia.

While Kemp's olive ridley turtle (Lepidochelys kempii) is the most threatened and rare species in the world. This species inhabits the Atlantic from the Caribbean Sea, passing through the Gulf of Mexico to the east coast of the United States..

Whale shark (Rhincodon typus)

Juvenile whale shark

It is a cartilaginous shark or fish up to 19 meters long with a front mouth with tiny teeth and filter pads. These fish feed by filtering the water and capturing plankton which includes tiny animals, fish eggs, algae, and protozoa, making them absolutely harmless to humans..

White shark (Carcharodon carcharias)

White shark (Carcharodon carcharias). Source: Terry Goss / CC BY-SA (

It is one of the largest and most aggressive sharks that exist, reaching up to 6 meters in length. On the other hand, they have a long life, reaching up to 70 years and living mainly in temperate waters and has been responsible for numerous fatal attacks on humans..

Tuna (Thunnus spp.)

Antarctic bluefin tuna

This genus groups 8 species known as true tunas, being fish with a metallic blue color on the back and silver white on the belly. The largest of the species is the Atlantic bluefin tuna (Thunnus thynnus), which reaches 2.5 meters in length and up to 680 kg in weight, and receives that name for the color of its meat, being highly demanded for human consumption.

Marlin or needlefish (family Istiophoridae)

Atlantic blue marlin

This name refers to 10 species of large fish that have a long lance-shaped snout and are characterized by their long and rigid dorsal fin. In the case of the Atlantic blue marlin (Makaira nigricans), reaches up to 5 meters in length and is highly appreciated as a trophy in sport and commercial fishing.

Puffer fish (family Tetraodontidae)

Blowfish. Source: Uploader1977 / CC BY-SA (

It is a family of fish whose strategy to defend themselves from predators is by inflating their body like a balloon. It covers more than 120 species that feed mainly on crustaceans and hard-shelled mollusks.

Most of these species are very toxic if their entrails and even their skin are consumed. In Japan they are a delicate delicacy, but experts are required to prepare them without their ingestion being dangerous..

Seahorse (genus Hippocampus)

Seahorse of the species Hippocampus Taeniopterus

The characteristic of this group of fish that make up 54 species is that they have a vertical body at right angles to the head. While the latter has a certain resemblance to the head of a horse, hence its common name.

Moray (family Muraenidae)

Moray eel of the species Muraena helena

They are a group of 200 species of very elongated fish with a prolonged dorsal fin until it joins the tail fin. They lack pectoral and pelvic fins, which give them a snake-like appearance, in addition to having rows of sharp teeth.

Coelacanth (Latimeria chalumnae)

It is a fish that inhabits the Indian Ocean, presenting an intense blue color with light blue spots, and reaching up to 2 meters in length. It is considered a living fossil, since evolutionarily it is closer to lungfish, amphibians, reptiles and mammals, than to common fish.

Octopus (order Octopoda)

Common octopus (Octopus vulgaris). Source: albert kok / CC BY-SA (

They are mollusks, therefore they have a soft body, and in this case they have a body and 8 tentacles. There are around 300 species of octopus, which are characterized by their good eyesight and their ability to pass through very narrow openings..

Octopuses have three hearts, one is in charge of general blood circulation. While the other two irrigate the gills so that the blood is oxygenated.

The common octopus (Octopus vulgaris) has a body of up to 25 cm with arms about 1 m long. This species lives in the Atlantic, and like all octopuses it covers its flight by expelling a dark ink.

Squid (superorder Decapodiformes)

Giant squid. Source: © Citron, wikimedia commons

These animals are related to octopuses, but they differ by presenting 10 tentacles instead of 8, being those of the genus Loligo those that are commonly caught and consumed. However, there are giant deep-sea species such as the giant squid (Architeuthis dux), up to 13 meters.

For its part, Antarctica inhabits the so-called colossal squid (Mesonychoteuthis hamiltoni), which reaches up to 10 meters and weighs up to 700 Kg.

Sperm whale (Physeter macrocephalus)

It is a mammal that inhabits all oceans, especially in temperate zones. Males can have teeth up to 20 meters long and their diet is based on giant squid and colossal squid..

Beluga (Delphinapterus leucas)

It is a mammal that lives in the Arctic Ocean, characterized by its white color and its head, in which it has an organ called melon. Males can measure up to 5 and a half meters and weigh more than 1,500 kilograms.

Crabs (infraorder Brachyura)

Red king crab (Paralithodes camtschaticus). Source: Sasha Isachenko / CC BY-SA (

They are crustaceans with 10 limbs (decapods), two of them form claws to defend, hunt and feed. One of the largest marine crabs is the king red crab (Paralithodes camtschaticus), which is captured in the bering sea.

There are also crustaceans called crabs that are not really, such as the so-called hermit crabs (superfamily Paguroidea). Lacking a shell, they are forced to live in an empty snail shell, which is why they are also called a thief crab.

Lobsters and lobsters (families Nephropidae and Palinuridae)

Lobster of the species Palinurus elephas

These are also crustaceans, but with elongated bodies with an obvious tail, among which is the European lobster or common lobster (Palinurus elephas) and the red lobster (Eunephrops bairdii) endemic to the Caribbean. Lobsters also belong to this group, such as the American lobster (Homarus americanus). All species highly valued in gastronomy.

Krill (order Euphausiacea)

Antarctic Krill

They are small shrimp-like crustaceans, in most cases they do not exceed 1 cm in length, although some species reach 15 cm. They are part of the plankton in all oceans, specifically zooplankton.

On the other hand, these small crustaceans are the food of the baleen or filter whales. They are distinguished from true shrimp because their gills are clearly visible from the outside.

Mussel (family Mytilidae)

Mussel of the species Mytilus californianus

This is a large family of bivalve mollusks, that is, soft-bodied marine animals protected by two shells. There are 52 genera that group together numerous species, most of which are commonly called mussels..

The shells are for the most part asymmetrical, elongated ovate and black in color. One of the edible species is the California mussel (Mytilus californianus).

Coral polyp (Anthozoa class)

Coral polyp

These invertebrates are the ones that form the so-called coral reefs, by segregating calcareous structures. They develop in tropical or subtropical marine waters that do not exceed 20 ° C, with sufficient lighting. The coral reefs that form the most diverse ecosystems in the seas.

Jellyfish (Scyphozoa class)

Jellyfish (Cyanea capillata). Source: Derek Keats from Johannesburg, South Africa / CC BY (

They are soft-bodied animals of very diverse species, but all characterized by presenting a jellyfish phase in their life cycle. That is, to form a body organism like an umbrella with numerous tentacles that moves according to the movement of the marine currents..

These tentacles have stinging cells with which they paralyze their prey. The largest of the species is Cyanea capillata, which reaches up to 2 meters in diameter.

Sea anemone (order Actiniaria)

Sea anemones with a clown fish

They are animals related to jellyfish and corals, formed by a base and a column that opens at the upper end where there is a disk surrounded by tentacles that can be retracted and a central mouth. Anemones are generally fixed in place, although they can move almost imperceptibly.

Sea urchin (class Echinoidea)

Sea urchin of the species Paracentrotus lividus

They are animals of radial symmetry from the group of echinoderms, which have a calcareous shell covered with long spines. They live attached to rocky substrates and coral reefs, moving slowly and feeding on sea grasses..

Among the numerous species are the purple sea urchin (Paracentrotus lividus) in the Mediterranean and the rock urchin (Echinometra lucunter) In the Caribbean.

Starfish (Asteroidea class)

Starfish of the species Choriaster granulatus

They have radial symmetry in the shape of a star with five broad arms, their body has a mouth at the bottom and is covered by hard plates with a surface of small spines or granular.

There are about 1,500 species, they breathe by diffusion, moving along the seabed or over corals, being found in all oceans and at almost any depth.

Sea spiders or brittle stars (class Ophiuroidea)

Sea spider (Gorgonocephalus eucnemis). Source: Ed Bierman / CC BY (

They are similar to starfish but their 5 arms are very thin and flexible, moving quickly through sinuous movements of their arms. There are more than 2,000 species that belong to this group of marine echinoderms.

One group of these animals is called basket stars, as their branching arms give the overall impression of being a wicker basket. The largest of these basket stars is Gorgonocephalus eucnemis.

Sponge (phylum Porifera)

Aplysina archeri

They are marine animals that remain attached to the substrate, breathing by diffusion through its walls and feeding by filtration. Your body is poorly differentiated and full of pores so that sea water circulates through it.

They are more or less cylindrical in shape with a central cavity and do not have defined organs. There are about 9,000 species in all the world's oceans.

Red-lipped batfishOgcocephalus darwini)

Fish of strange morphology that stands out for its bright red lips and its pectoral fins that allow it to move through the sand. It is endemic to the Galapagos Islands (Ecuador) and some coastal areas of Peru.

Due to its structure, it moves in depths not exceeding 70-80 meters, with reefs and sandy areas being the most comfortable locations for this fish..

Its striking red lips curved downwards give the fish an angry look, but its function is the complete opposite, since it serves as a sexual attraction..

Eel shark (Chlamydoselachus anguineus)

Eel shark. Source: © Citron, wikimedia commons

Uncommon species located randomly in different parts of the Atlantic and Pacific Oceans. It lives in the depths, specifically on the continental slope and the outer continental shelf.

It is characterized by its primitive morphology, being in some cases confused with a living fossil. It measures between 3 and 4 meters and weighs 8-10 kg depending on the specimen. They are carnivores and can have up to 12 young per gestation. 

Drop fish (Psychrolutes micropores)

It is located in the waters of New Zealand and Australia more than 1000 meters deep in the abyssal zone. It stands out for its jelly-like skin and wide mouth and trunk.

There is little information about this species, since entering its habitat is difficult. The individuals captured so far weighed less than 2 kg and, taking into account their morphology, it is thought that they are an ambush predator.


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