por 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 a 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.
However, in general terms, marine biodiversity is much lower than terrestrial, mainly due to the greater uniformity of the environment. Another limiting factor is the scarcity of some determining resources such as light.
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What are the marine animals?
The essential characteristic of marine animals is the fact that they require a medium composed of water with a high salt content to live. This requires a series of adaptations that allow them to inhabit that 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 ascending to the surface to breathe air. In addition, aquatic animals must withstand variable 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 a spinal column and skull. Covering in the first group fish, reptiles, mammals and seabirds. While invertebrates constitute the largest group, including marine worms, sponges, echinoderms, crustaceans, and mollusks.
Characteristics of marine animals
Breathing
Since marine animals live in an aquatic environment, they are faced with the problem of breathing in the oxygen vital to their existence. In this environment, the oxygen is dissolved in the water, so a different respiratory system is required from that of 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 come to the 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 highly salty water, 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 outside, taking into account that the cells lose water (they become dehydrated), in media with a high concentration of salts.
Temperature
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 moving 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 them warm.
Types of marine animals
To simplify, marine animals can be separated into two large groups, a natural one called vertebrates and another called invertebrates, which includes 95% of marine animals.
vertebrates
In the group of vertebrates are all those marine animals that have a skull and spine. Among these are fish, marine reptiles and marine mammals, as well as seabirds.
Among the fish are bony (tuna, hake), cartilaginous (sharks, rays) and jawless fish (lamprey, hagfish). While reptiles include sea turtles and sea snakes.
Vertebrate marine mammals are represented by cetaceans (whales, dolphins, orcas), mermaids (manatees), phocids (seals) and otariids (lions and sea lions). Regarding seabirds, although they do not live strictly in seawater, they are considered marine animals because they require this environment to feed.
invertebrates
It groups all the other marine animals that are not interpreted as vertebrates because they do not have an internal articulated skeleton, neither bone (bones), nor cartilage. This includes arthropods, such as crustaceans, molluscs (oysters, octopus, squid), echinoderms (starfish and sea urchins), and porifera (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
The blue whale (Balaenoptera musculus) is the largest living animal on the planet.. Their main food is microscopic crustaceans, similar to tiny shrimp called krill.
dolphins
There are about 30 species of marine dolphins, some small, such as the Heaviside’s dolphin (Cephalorhynchus heavisidii), larger ones, such as the bottlenose or bottlenose dolphin (Tursiops truncatus). Others larger to the point that they are called whales, such as pilot whales (globecephala), but that they are large dolphins.
Orca (Orcinus orca)
Although they are associated with whales, the orca also belongs to the family of marine dolphins. In fact, it is the largest dolphin, 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 orca, 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 are captured by a specialized organ, being able to establish sizes and distances.
Narwhal (Monodon monoceros)
It is another very peculiar toothed whale due to a tusk that grows as if it were a long and straight frontal horn up to 3 meters long, 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 (family Phocidae)
Except for the freshwater Baikal seal, seals are a family of marine mammals, almost entirely of temperate and cold climates. Only monk seals inhabit tropical and subtropical climates, including the Mediterranean monk seal (Monanchus monanchus) and those of the genus Neomonachus in Hawaii (Neomonachus schauinslandi) and the Caribbean (Neomonachus tropicalis).
These animals are more efficient swimmers than their relatives the walruses and sea lions, but clumsier on land. On the other hand, they lack ears, hence they are also called earless seals.
Sea lions and sea lions (family Otariidae)
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 inhabits mainly the island of Guadalupe, Mexico.
Sea snakes (subfamily Hydrophiinae)
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 coloration. In addition, they breathe through lungs, so they must come to the surface to breathe.
sea turtle (family Cheloniidae)
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 endangered. 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 Kemp’s ridley (Lepidochelys kempii) is the most endangered 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)
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.
Great white shark (Carcharodon carcharias)
It is one of the largest and most aggressive sharks that exists, reaching up to 6 meters in length. On the other hand, they have a long life, reaching up to 70 years and live mainly in temperate waters and have been responsible for numerous fatal attacks on humans.
Tuna (Thunnus spp.)
This genus groups 8 species known as true tunas, being metallic blue fish on the back and silvery 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 from the color of its meat, being highly demanded for human consumption.
Marlin or needle fish (family Istiophoridae)
With this name reference is made to 10 species of large fish that have a snout in the shape of a long spear and are characterized by their rigid and long dorsal fin. In the case of the Atlantic blue marlin (makaira nigricans), can reach up to 5 meters in length and is highly prized as a trophy in sport and commercial fishing.
Pufferfish (family Tetraodontidae)
It is a family of fish whose strategy to defend itself against predators is to inflate its body like a balloon. It includes more than 120 species that feed mainly on hard-shelled crustaceans and molluscs.
Most of these species are very toxic if their viscera and even the 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)
The characteristic of…