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Glossary - Marine Life and Marine Biology Terms

Learn definitions of marine life terms and scientific terms pertaining to marine life and marine biology in this glossary.

An adaptation is a physical or behavioral characteristic that has developed to allow an organism to better survive in its environment.

The definition of the term ambergris, as related to marine biology.

Definition of the term Antarctic - the southernmost portion of the Earth.

Apex Predator
An apex predator is an animal who, as an adult, has no natural predators in its ecosystem. The great white shark is an example of an apex predator. Apex predators play an important role in keeping ecosystems in check. Learn more about apex predators and why they are important.

Definition of the term Arctic, including the Arctic region and examples of animals that live in the Arctic.

Aristotle's Lantern

 Aristotle's lantern is a feeding structure used by some echinoderms. Learn more about Aristotle's lantern, how it was named, and where it is located.

Definition of arthropoda, which is a group of organisms. Learn about arthropoda and examples of marine life that are arthropods.

Definition of the term Ascidiacea and examples of animals that are ascidaceans.

Definition of the term Ascidiacea and examples of animals that are ascidaceans.

Baleen is a strong, yet flexible material made out of keratin, a protein that is the same material that makes up our hair and fingernails.

The term beak may be used both when referring to birds, and to cephalopods.

Definition of the term bioerosion, as used in referring to marine life.

Bilateral Symmetry
Definition of bilateral symmetry, along with examples.

Definition of the marine life term biology.

Definition of bioluminescence.

A bivalve is an animal that has two hinged shells. Examples of bivalves are clams, mussels, oysters and scallops. Learn more about bivalves here.

Definition of the term blow, as used to refer to cetaceans (whales, dolphins and porpoises).

A blowhole or blowholes are the the "nostrils" of a whale.

Blubber is a fat layer underneath an animal’s skin. Blubber is composed of fat-filled cells and functions both to insulate and to store food reserves. Animals that have blubber include whales, seals and walruses.

Definition of the term bolus, as it relates to marine life. A bolus is a pellet made up of objects a bird can't digest, such as squid beaks, sticks, or litter items.

Definition of the marine life term brackish. What is brackish and who lives in this type of environment?

Bycatch describes animals caught unintentionally by fishing gear, including non-target species and undersized fish. Many fishermen seek to catch a "target" species. When fishermen catch something that they didn't intend to, such as a different fish species, a whale or dolphin, sea turtle or seabird, that is called bycatch.

Byssal (Byssus) Threads
Byssal, or byssus threads are strong, silky fibers made from proteins that are used by mussels to attach to rocks, pilings, or other substrates.

Learn the definition of callosity, and where callosities are found.

A carapace is a shell on an animal’s back, or part of its back.

A carnivore is an animal that eats flesh, which also can be referred to a "meat-eater." The word carnivore can also be used to specifically describe animals in the Order Carnivora, which includes cats, dogs, seals, walruses and a variety of other mammals.

Cartilage is a tough, flexible tissue, which is softer than bone. In humans, cartilage forms a temporary skeleton in the fetus and infant, and is later replaced by a bone skeleton.

Definition of the marine life term cephalopod

Cerata are a projection found on some nudibranchs. Learn about cerata and their function.

"Cetacean" is the word for all mammals in the order Cetacea, which includes whales, dolphins and porpoises.

Learn about the chiton, an animal that is a mollusk in the Class Polyplacophora. Although they may look a bit like bugs or scaled worms, chitons are animals in the Phylum Mollusca, which means that they're related to such diverse organisms as octopuses, squid, clams, mussels, and nudibranchs.

Chordata is the phylum that includes all the animals that have a notochord, or nerve cord, at some stage of their development. Animals in this phylum are known as chordates. The most well-known chordates are the vertebrates - animals that have a spine.

Chromists - Kingdom Chromista
The Kingdom Chromista contains plant-like organisms that possess chlorophyll a and c and other pigments that give them their yellow-brown color (fucoxanthin). Examples of chromists: brown algae (e.g., kelp), water molds, diatoms.

CITES (Convention on International Trade in Endangered Species)
CITES is an acronym that refers to the Convention on International Trade in Endangered Species, an international treaty that formed an agreement regarding trade in specimens of wild animals and plants. Currently, CITES regulates trade in over 30,000 species of organisms and wildlife products (e.g., food products, exotic leather, and medicines.) Learn more about CITES here.

Definition and information about the term clasper, a reproductive organ used by sharks and rays.

Class Polyplacophora - the Chitons
Information on Class Polyplacophora, the taxonomic class that contains the chitons. The tongue-twister Polyplacophora is Latin for "many plates." The animals in this class are commonly known as chitons, and they have eight overlapping plates, or valves, on their flat, elongated shell. There are about 800 species of chitons.

Cnidaria is a classification phylum that includes corals, sea anemones, sea jellies (jellyfish), sea pens, and hydras. Cnidarians are radially symmetrical and have tentacles with stinging structures called nematocysts.

Copepods are crustaceans, considered part of the plankton, and are an important prey item for fish, whales and other organisms. There are thousands of copepod species and they range throughout the world, in both fresh and saltwater. Learn more about the marine life term copepod here.

Corals are animals in the Phylum Cnidaria. Cnidarians also include sea fans, sea pansies and anemones. Corals are in the class anthozoa, and can be divided further into the stony corals - Order Scleractinia, the builders of coral reefs, and soft corals - Order Alcyonacea, which are soft or leathery and include species such as bubblegum corals and mushroom corals.

Countershading is a type of coloration commonly found in animals, and means that the animal's back (dorsal side) is dark while its underside (ventral side) is light.

Dead Zone
A 'dead zone' is an area of low oxygen, where marine life can't thrive. The dead zone may be caused by an excess of nutrients - eutrophication - that results in a decrease in dissolved oxygen. The best example of a dead zone in the U.S. is the Gulf of Mexico dead zone, which occurs each year in the late spring and summer

=Delphinidae is the family of animals commonly known as the dolphins. The animals in the delphinidae are some of the most recognizable species of marine life, and includes species such as the bottlenose dolphin and (perhaps surprisingly) the killer whale (orca). Cetaceans in the Family Delphinidae are Odontocetes, or toothed whales. There are...

Dermal Denticle
Dermal denticles (placoid scales) are tough scales that cover the skin of elasmobranchs (sharks and rays). Even though denticles are similar to scales, they are really modified teeth and are covered with a hard enamel.


What is a dinoflagellate? Learn about dinoflagellates, how many dinoflagellate species there are and examples of dinoflagellates.

Dorsal Fin
Definition of dorsal fin. Learn where a dorsal fin is located and examples of animals with dorsal fins.

Definition of dorsum.

Earth Day - April 22
The first Earth Day was celebrated on April 22, 1970. The idea was proposed by Wisconsin Senator Gaylord Nelson amid growing concerns about air and water pollution and other environmental problems. Learn more about the history of Earth Day here.

Toothed whales, such as dolphins, porpoises and orcas, make high-frequency sounds that bounce off of whatever is in front of them, including prey, terrain and obstacles. They receive these sounds and can sense the size, shape, density, distance and even the texture of the object in front of them. This is called echolocation.

Definition of ectothermic. An ectothermic animal is one who cannot regulate its own body temperature, so its body temperature fluctuates according to its surroundings.

The term elasmobranch refers to the sharks, rays and skates, which are in the subclass Elasmobranchii and class Chondrichthyes. The Condrichthyes class includes only one other subclass, the Holocephali (chimaeras), which are unusual fish found in deep water.

Electro-Reception - What is Electric Sensitivity?
Cartilaginous fishes like sharks and rays have an electro-receptor system, that is a finely-tuned sensitivity to electrical fields. Sharks and rays have tiny pores on their skin that attach to long tubes containing a jelly-like fluid with a sensory nerve cell at the end, called ampullae of Lorenzini.

Definition of endothermic. Endothermic animals are those that must generate their own heat to maintain their body temperature. These animals are commonly referred to as warm-blooded.

Definition of the word estuary - what is an estuary, where would you find an estuary and what kinds of marine life are found in an estuary.

Evolution is the process by which species change over a long period of time

Definition of the marine life term flipper - what is a flipper, where is it located and how is it used. What marine animals have flippers?

In marine biology terms, a foot is a muscular appendage found in mollusks. Learn more about the mollusk foot and how it is used.

Gestation Period
Definition of the marine life term gestation period

Gills are structures used by an aquatic organism to breathe.

An herbivore is an organism that feeds on plants. This organism is referred to as herbivorous.

Herbivorous organisms are those that feed on plants. The word herbivorous comes from the Latin word herba, meaning grass, and vorus, meaning "feeding on.

In marine life terms, a hermaphrodite is an organism that is neither male nor female - it has both male and female sex organs. Learn more and see examples of hermaphroditic organisms.

The term hermaphroditic refers to an organism that has both male and female sex organs - the organism doesn't have separate genders (isn't male or female).

A holdfast is the root-like structure at the base of an algae (seaweed) that fastens the algae to a hard substrate. Holdfasts are prominent in brown algaes and seaweeds such as kelp.

A hybrid is an offspring of parents that are two different species or subspecies.

ICCAT (International Commission for the Conservation of Atlantic Tunas)
Information about ICCAT, the International Commission for the Conservation of Atlantic Tunas.

An ichthyologist is a scientist who studies fish.

Ichthyology is the branch of zoology that involves the study of fish.

Definition of the term invertebrate, as used in marine biology. Learn about invertebrates - where invertebrates live, what they look like, and examples of invertebrates.

Keratin is a strong protein that makes up whale baleen, and the hair, nails and hooves of other animals.

The term lunate refers to "crescent-shaped." In a marine biology sense, it can refer to the shape of a fish's tail, which can be said to be lunate (the upper and lower "lobes" of the tail fin are about equal in size) or non-lunate (one lobe is longer than the other.)

Definition of madreporite, an opening in an echinoderm. Learn more about what a madreporite does and the organisms in which it is present.

Definition of mammal. Characteristics of mammals and examples of mammals.

What is a mandible? Learn about the term mandible and how it relates to marine life.

The mantle is an important part of the body of a mollusk. It forms the outer wall of the mollusk's body and encloses the mollusk's visceral mass (internal organs), and secretes calcium carbonate to form the mollusk's shell.

Marianas Trench
Learn about the Marianas Trench, also called the Mariana Trench.

Marine Biogeographer
A marine biogeographer is a scientist who studies the geographic distribution of marine animals and plants in the marine environment.

Marine Biologist
Learn the definition of the term marine biologist, along with what it takes to become a marine biologist, what marine biologists do, and how much marine biologists get paid.

Marine Biology
Definition of the marine life term marine biology.

Marine Debris
Marine debris is something in the marine environment (such as in the ocean or on the beach) that doesn't naturally occur there. Learn the definition of marine debris, examples of marine debris, and threats of marine debris and how you can prevent them.

Marine Mammal Protection Act
Learn about the Marine Mammal Protection Act.

Marine Protected Area
Marine Protected Areas (MPAs) are used to protect natural and/or cultural areas from human impacts and to help sustain important habitats. One MPA may be much different from another in terms of restrictions and management approaches.

Definition of the term maxillae (the plural of maxilla).

Maximum Sustainable Yield (MSY)
The maximum sustainable yield (MSY) is a term often used in fisheries management.

Migration in marine animals involves the movement from one area to another, and back again. This movement is usually related to food availability or reproduction. Learn about migration and marine animals who migrate.

A mollusk is an animal classified in the Phylum Mollusca. Here you can learn more about mollusks and find examples of mollusks. This extremely diverse animal phylum is thought to contain well over 100,000 species, which include animals in the taxonomic classes Polyplacophora (chitons), Gastropoda (animals with one shell, including snails, limpets, and sea slugs/nudibranchs), Bivalvia (animals with two shells - clams, mussels and oysters) and Cephalopoda (octopuses and squids).

Mutation is an accidental change in an organism’s gene or chromosome that results in a new trait.

Information about the marine life term mysticeti, which refers to a group of whale species that have a specific feeding mechanism - baleen.

Information about the marine life term mysticeti, which refers to a group of whale species that have a specific feeding mechanism - baleen.

A necropsy is a dissection of the dead body of an animal to determine the cause of death. Necropsies can help us learn more about the biology of an animal, how it is affected by disease or how human interactions may impact animals.

Nekton is the term that refers to the "swimmers," the animals in the ocean that can move independently of ocean currents, by swimming or using another form of locomotion. This means that, unlike plankton, they are capable of determining their location in the ocean.

Definition of notochord, including examples of animals that have a notochord.

The word odontocete refers to in the suborder Odontoceti, or "toothed whales." Learn more about the characteristics of toothed whales and toothed whale species.

An omnivore is an organism that eats both animals and plants. Learn more about omnivores and examples of omnivores in the marine environment.

Definition of Ophiuroidea, the group of echinoderms that contains the brittle stars and basket stars.

Overfishing is, simply put, when so many fish are caught that the population can't reproduce enough to replace them. Overfishing can lead to depletion of or extinction of fish populations.

Ovoviviparous animals produce eggs, but instead of laying the eggs, the eggs develop within the mother's body.

Information on the marine life term pearl - how pearls are formed and where they can be found.

Pectoral Fin
Definition of pectoral fin.


 Learn about pedicellariae, where they are found and how they are used. 

A pheromone is a chemical produced by some animals that cause specific reactions in other animals.

The term phylum is one of seven major categories that are used to classify organisms. In order of broad to specific, these seven categories are: Kingdom, Phylum, Class, Order, Family, Genus, and Species. This classification system was developed by Carolus Linnaeus in the 18th century

Placoid Scales
Placoid scales (dermal denticles) are tough scales that cover the skin of elasmobranchs (sharks and rays). Even though placoid scales are similar to the scales of bony fish, they are really modified teeth and are covered with a hard enamel.

"Plankton" is the term that generally refers to the "floaters" - the organisms in the ocean that drift with the currents. This includes the algae, zooplankton ("animal plankton"), phytoplankton (plankton that are capable of photosynthesis) and bacteria.

Polyps are the base of coral reefs. They have a soft, tube-like body and a mouth surrounded by a ring of tentacles. Learn more about coral polyps here.

Pneumatocyst (Air Bladder)
Pneumatocysts, or air bladders, are gas-filled sacs in an algae that that float the algae's blades up toward the water's surface, providing greater access to sunlight for photosynthesis.

When referring to marine life, a pod is a group of animals, such as whales or dolphins. Learn more about pods here.

A predator is an organism that hunts and kills other organisms for food. Learn more about predators and examples of ocean predators.

A body part that is prehensile is one that is adapted for grasping or seizing.

Definition of prey, as used in describing marine life.

Protists are organisms in the kingdom Protista. These organisms are eukaryotes, meaning they are made up of single or multiple cells which all contain a nucleus enclosed by a membrane.

Radial Symmetry
Definition of radial symmetry. Learn what radial symmetry is and in which marine organisms it occurs.

The radula is a special structure used by many molluscs to scrape food off rocks or create depressions in rocks that the mollusc uses for habitat.

Definition of the marine biology term rhinophore. Learn about rhinophores and where they are found.

Definition of the marine life term rookery

A rorqual is a baleen whale with a dorsal fin and throat pleats, or grooves, that extend from the whale’s lower lip down past its flippers.

The term rostrum is defined as an organism’s beak or a beak-like part. In cetaceans...

The basic definition of salinity is the amount of salts dissolved in water.

A scute is a piece of keratin that forms the shell of 6 of the 7 species of sea turtles.

A seamount is an underwater mountain. The base of the seamount is on the seafloor and its summit doesn't reach the water surface. There are thousands of seamounts located throughout the world's oceans.

Definition of the word sessile, as used in a marine life context.

Sexual Dimorphism
Definition of the marine life term sexual dimorphism, with examples.

Sirenians are mammals in the Order Sirenia, which includes manatees and dugongs. These animals are herbivorous, and have two forelimbs and a flattened tail.

Spiracles are found in bottom-dwelling sharks and rays. They are a pair of openings just behind the animal's eyes that allow the it to draw oxygenated water in from above.

A spout is the visible exhalation of a whale. Learn more about whale spouts here.

Stellwagen Bank National Marine Sanctuary
Stellwagen Bank National Marine Sanctuary (SBNMS) is an 842-square mile underwater sanctuary located north of Cape Cod, Massachusetts. The sanctuary was named for one of its most prominent features - Stellwagen Bank, a 19-mile long sandy plateau that stretches from south of Cape Ann, MA to Cape Cod, MA. At a depth of about 100-120 feet, Stellwagen Bank is also one of the shallowest features in th…

Definition of subphylum.

A subspecies describes a group of related organisms that can interbreed and are geographically distinct from others in their species.

Definition of tentacle, and examples of marine animals that have tentacles.


 No, we're not talking about an exam here, but the "shell" of some organisms. Learn which ones. 

Tidal Pool
A tidal pool, also commonly called a tide pool, is water left behind when the ocean recedes at low tide.

Tide Pool (Tidepool)
A tide pool is a puddle of water left when the ocean recedes. This occurs as the tide turns from high tide to low tide. Learn more about tide pools.

Definition of topography.

Tube Feet

 What are tube feet and how do they work? Learn here. 

Turtle Excluder Device (TED)
Turtle excluder devices (TEDs) were created to protect sea turtles from getting caught in shrimp nets. The TED is attached to a shrimp trawling net and is a grid of metal bars that has an opening at the top or bottom, creating a hatch that allows sea turtles and larger fish to escape. Small animals such as shrimp go between the bars and are caught in the end of the trawl.

Definition of the term tusk, as used in the context of marine life. Learn the marine species that have tusks.

In marine life terms, a veliger is a planktonic larvae. Some mollusks, including gastropods, have a veliger stage.

Definition of ventral.

Definition of the term viviparous. Learn about the term viviparous, and examples of viviparous marine life.

Information on whelks, which are snails in the Class Gastropoda. Whelks are snails, but you can easily conjure an image of a whelk to mind if you think of the term 'sea shell.' There are over 50 species of whelks. Whelks are carnivorous, and eat mollusks, worms and crustaceans.

Zoology is the scientific study of animals.

What are phytoplankton? Learn about phytoplankton, examples of phytoplankton and its role in climate change.

What are phytoplankton? Learn about phytoplankton, examples of phytoplankton and its role in climate change.

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