The non-living component(s) of an organism’s environment.
The end of a coral away from, or opposite, the mouth.
Hills that arise from abyssal plains.
Areas that appear to be flat that are found between the continental rise and the mid-ocean ridges.
The area of the ocean that ranges from depths of 10,000-20,000 feet (3,000-6,000 meters).
(Adenosine diphosphate) A molecule consisting of adenosine with two phosphate groups attached that is formed into ATP to store energy through the process of cellular.
The highest point of a coral reef that resides between the back and the fore reef that is dominated by calcareous red algae.
The study of the body including cells, tissue, organs, and systems.
Caused or produced by humans.
An organism that resides at the top of the food chain and has few to no predators. They help regulate the food chain.
One of the three domains, which consists of unicellular microorganisms that do not contain a cell nucleus or membrane-bound organelles in their cells. They often live in extreme environments and include methanogens, extreme halophiles, and hyperthermophiles.
A form of reproduction where a new organism arises from a single organism. It does not involve gametes and the offspring is an identical clone of the parent.
(Singular: spawner) A type of sexual reproduction when organisms, such as corals, may spawn during a synchronous spawn, but are more likely to spawn before or after it.
An oval, circular, or horseshoe-shaped coral reef, which contains a coral rim that partially or completely encloses a lagoon.
The most basic unit of chemistry. Atoms of different elements have a different number of protons, neutrons, and electrons.
(Adenosine triphosphate) A molecule consisting of adenosine with three phosphate groups attached that is used to store energy for cells.
Organisms that create their own food using light or chemical energy. Also referred to as a producer.
An area that slopes into a lagoon and is present in barrier reefs and atolls.
(Singular: bacterium) One of the three domains, which consists of unicellular microorganisms that do not contain a cell nucleus or membrane-bound organelles in their cells. They include gram-positive and gram-negative bacteria, mycoplasmas, and cyanobacteria.
A form of asexual reproduction where a single polyp abandons its colony and settles on substrate to create a new colony.
An isolated reef, often found on top of underwater hills. They do not have a coral rim and are often crescent-shaped with a wide blanket of sediment behind it. Also referred to as a platform reef.
A coral reef that is separated from shore by a lagoon. Typically, they grow along the outer edge of the continental shelf, running parallel to the shoreline. They are further off shore than fringing reefs.
The first skeletal element deposited by a planula. This anchors corals to the substrate; located aborally. It is also the area where hard corals secrete calcium carbonate. Also, referred to as the basal plate.
The first skeletal element deposited by a planula. This anchors corals to the substrate; located aborally. It is also the area where hard corals secrete calcium carbonate. Also, referred to as the basal disk.
The study of the depth of underwater structures on the floor of lakes and the ocean.
Animals without a spinal cord or backbone that live in or on sediments on the bottom of the ocean floor.
Literally, a two-name naming system. The formal naming of organisms that includes the genus and species name. Also referred to as Latin name or scientific name.
A natural science concerned with the study of life and living organisms.
An ecological level of organization that consists of several different ecosystems that are geographically and climatically defined.
An ecological level of organization that contains all biomes on Earth.
The living or once living component(s) of an organism's environment.
(Singular: branch) The lines of a cladogram that represent evolutionary lineage.
A coral growth form that forms branches. These branches can also grow branches called secondary branches.
(Singular: spawner) A type of sexual reproduction when organisms, such as corals, release their gametes into the water at the same time. Also referred to as mass spawners and synchronous spawners.
A type of sexual reproduction where corals fertilize gametes in their gastrovascular cavity, allowing them to grow into planulae before being released into the water column.
A type of asexual reproduction where a portion of the parent polyp pinches off to form a new individual.
The ability to float.
The rate at which coral absorbs calcium from seawater to create their hard 'skeletons.'
Calcium Carbonate (CaCO3)
A chemical compound with the chemical formula CaCO3. Organisms such as corals, marine shelled organisms, and algae incorporate it into different structures like their shells and 'skeletons.'
Calcium Carbonate Saturation
[kal-see-uhm kahr-buh-nayt sach-ur-ay-shuhn]
The amount of calcium and carbonate in the ocean.
An organism that feeds on other animals.
Swedish scientist (1707-1778) who developed a hierarchical naming system that led to the modern classification system. He is often referred to as the "Father of Taxonomy."
A series of events that allows a cell to divide and replicate.
When a parent cell divides into two daughter cells.
A scientific theory that states all organisms are composed of one or more cells, cells are the most basic unit of life, and cells can only arise from other living cells.
The process of breaking down glucose to release the energy that is stored in it. The chemical reaction equation is C6H12O6 + O2 → CO2 + H2O + energy.
A cylindrical organelle that consists of microtubules. It helps to anchor the spindle fibers during cell division.
The area on the chromosome where the kinetochores attach during cell division and that connects the chromatids together.
Replicates during interphase. It is part of the spindle and contains two centrioles. During cell division, they migrate to opposite poles and aid in pulling apart the chromosomes.
A process where molecules are being rearranged to produce something new.
The area where crossover takes place (genetic material is exchanged) during meiosis.
Each half of a chromosome when it is longitudinally divided. Contains a double helix of DNA.
(Singular: chromosome) Long strands of molecules called DNA.
(Singular: cilium) Short, hair-like projections that help aid organisms like planula larvae to move.
A group of organisms that includes ancestors and all descendants of that ancestor.
A diagram that is used to demonstrate evolutionary relationships among organisms. Also referred to as a phylogenetic or evolutionary tree.
A broad term that means organization of biological information.
An indentation of the cell’s surface that forms as the cell prepares for division.
A method that corals use to obtain zooxanthellae when corals directly transfer zooxanthellae to their offspring.
A phylum which contains anemones, corals, hydrozoans, and jellyfish.
A hair-like projection located externally on the operculum of a nematocyst that, when stimulated, triggers the operculum to open.
The tissue that connects colonial coral polyps and contains structures that allows corals to share nutrients.
(Singular: coral) Corals that mainly thrive in higher latitudes at depths that can reach over 6,600 feet (2,000 meters). They are sometimes referred to as deep-water corals.
A growth form where corals are cylindrical in shape and grow upwards. They often look like fingers. They do not have secondary branches. Also referred to as digitate.
A type of symbiosis where one organism benefits and the other is neither benefiting nor being harmed.
A name given to an organism that is used for simplicity instead of the scientific name. Can vary depending on the geographic location and culture. Also referred to as the vernacular name.
An ecological level of organization that includes populations of different species that live in a defined area.
A molecule that contains two or more different elements. An example is water (H2O) which has two different elements - hydrogen and oxygen.
A layer of crust that forms continents and extends all the way out to the continental shelf in the ocean.
An area that makes up the continental shelf, continental slope, and continental rise.
The area between the continental slope and the abyssal plain formed by an accumulation of sediment and dead organisms that are transported from the continental shelf and slope.
An area that gently slopes from continents (or around islands) and extends to the continental slope.
An area in between the continental shelf and the continental rise that steeply drops off.
Coral Reef Geomorphology
[kohr-l reef jee-oh-mohr-fol-oh-jee]
The study of the distribution, reef morphology and bathymetry, processes that control reef formation, and reef location in relation to land forms.
(Singular: alga) A type of algae that uses calcium carbonate to build their cell walls.
The cup-like skeleton of an individual polyp that creates stability for the polyp.
An organism that feeds on coral polyps.
The process of exchanging chromosome segments (genetic material) during meiosis.
A coral growth form that adheres to rocky substrates. They do not grow upwards, they grow outward, covering the rocky substrate. Also referred to as encrusting.
Division of the parent cell into two daughter cells during cell division.
The new cells formed when a cell divides. In mitosis, the cells are identical, but in meiosis they have different genetic content.
(Singular: lineage) Taxa that descend from the same ancestor.
An organism that breaks down dead or decaying organisms, as well as waste.
Deep Ocean Current
[deep oh-shn kur-nt]
Currents that occur in the ocean at depths greater than 300 feet (100 meters). They are driven by density, temperature, and salinity gradients.
Deep Water Layer
[deep wah-tur lay-ur]
The layer of water below the thermocline that slowly decreases in temperature as depth increases.
Long, narrow asymmetrical depressions that run parallel to continental margins or volcanic islands.
(Singular: coral) Corals that mainly thrive in higher latitudes at depths that can reach over 6,600 feet (2,000 meters). They are sometimes referred to as cold-water corals.
A physical property of matter that measures the concentration of matter for an object. Often referred to as how closely “packed” or “crowded” the material appears to be.
A trait that has evolved in a lineage and the trait appears in later organisms, but not earlier ones.
An organism that feeds on decaying plant and animal matter, as well as waste.
A tool used to help identify unknown organisms based on a series of two possible choices that leads the user to correctly identify organism(s).
A growth form where corals are cylindrical in shape and grow upwards. They often look like fingers. They do not have secondary branches. Also referred to as columnar.
A cell that contains two copies of chromosomes, one from each parent.
Dissolved Organic Matter (DOM)
[dih-zolvd ohr-gan-ihk ma-tur]
A mixture of organic molecules (those that contain both carbon and hydrogen atoms) that are found in seawater.
The geographic area in which a species can be found.
Diurnal Vertical Migration
[di-ur-nl vur-tih-kl mi-gray-shuhn]
Movement up and down in the water column within a 24 hour period.
The area of a coral reef that increases greatly with depth, almost extending straight down.
Stands for ecological art. Generally, it’s artwork that expresses conservation and education about the environment and helps propose new ways of people co-existing with nature.
The scientific study of the distribution and abundance of life and the interactions between organisms (living) and their natural environment (non-living).
An ecological level of organization that includes all of the biotic (living) factors, the abiotic (nonliving) factors, and how they interact.
Outer cell layer of a polyp that houses nematocysts and secretes mucus. Corals only have two major layers of tissue.
A symbiotic relationship where one organism lives on the body of another organism.
A fertilized egg in an early stage of development that has begun cell division.
In hierarchical biological organization, a property that shows up that isn't in the previous level, making each level more complex than previous ones.
A coral growth form that adheres to rocky substrates. They do not grow upwards, they grow outward, covering the rocky substrate. Also referred to as crustose.
Inner cell layer of a polyp that houses zooxanthellae. Corals only have two major layers of tissue.
A symbiotic relationship where one organism lives inside another organism.
The domain that consists of organisms with cells that contain complex structures enclosed within membranes, like a nucleus.
An organism whose cells contain a nucleus or other structures enclosed within membranes.
The upper layer of the ocean that receives sunlight allowing for photosynthesis to occur.
A diagram that is used to demonstrate evolutionary relationships among organisms. Also referred to as a phylogenetic tree or cladogram.
Hard outer covering of the body occurring in some invertebrate organisms.
A type of asexual reproduction where a bud forms outside the parent polyp's ring of tentacles, producing a smaller polyp.
A symbiotic relationship where organisms can survive without the relationship, but it increases the chances of survival.
The process of two different gametes (a sperm and an egg) combining to form a zygote.
A type of asexual reproduction where some coral colonies have the ability to split into two or more colonies, during early developmental stages.
A growth form where corals look like layered petals in an open flower.
A growth form where corals look like layered petals in an open flower.
A series of food chains that make up an ecological community. It depicts the feeding connections in this community.
The area of a coral reef that is the furthest distance from shore and on the oceanic side of the reef crest. Also referred to as the reef front.
Form Fits Function
[fohrm fihts fuhnk-shuhn]
Describes how organisms and/or their structures are designed to perform a particular function(s).
A type of asexual reproduction when a coral is intentionally or unintentionally broken off from the parent coral.
A growth form where coral polyps are individuals (not colonial). They are typically round, oblong, or oval.
A type of reef where corals colonize near the shoreline of continents or islands and do not contain a lagoon.
Mature sexual reproductive cells; sperm and eggs.
Gap 1 (G1)
Growth Phase One, the first phase of interphase, is when the cell grows, doubling in mass and organelles, in preparation for cell division.
Gap 2 (G2)
Growth Phase Two, the third phase of interphase, is when proteins are replicated. They will help the cell to divide in meiosis. At the end of this phase, the cell is ready to enter meiosis.
The inner cell layer derived from the ectoderm that lines the gastrovascular cavity, absorbing nutrients, excreting mucus and waste, and allowing for gas exchange and reproduction.
(Singular: canal) Canals located in the coenosarc that allow polyps to share nutrients and zooxanthellae.
A simple sack where the stomach is located; it’s simple because corals do not have an anus. It is used to absorb nutrients, excrete mucus and waste, gas exchange, and reproduction.
The study of the origin and evolution of the Earth’s topography and bathymetry.
(Geographic Information System) A tool used by scientists and other experts to display and analyze a large data set that is linked to a latitude and longitude.
Global Ocean Conveyor Belt
[gloh-bl oh-shn kon-vay-ur belt]
Large-scale ocean circulation that is driven by salinity and temperature. It is formally referred to as thermohaline circulation.
A chemical compound with the chemical formula C6H12O6. A simple sugar that organisms use as a source of energy. It is produced during photosynthesis and broken down during cellular respiration.
Describes the shape of a coral.
Seamounts that have been eroded, becoming flat on top.
A cell that contains one copy of unpaired chromosomes (half the number of the parent cell).
An organism that feeds on plants.
An organism that has both male and female sex organs, producing both sperm and eggs.
Organisms that cannot create their own food and must eat other organisms to survive.
(Singular: hexacoral) A subclass of the class Anthozoa that is comprised of corals with six-fold symmetry. Hexacorals are hard or stony corals.
One paternal and one maternal chromosome that pair up during meiosis.
Areas of volcanism that produce magma, which flows from the Earth’s mantle.
When salinity is greater than 40 parts per thousand (ppt).
Drawing a conclusion based off of past experiences and observations.
Elements or compounds that don’t contain carbon and hydrogen atoms. Some examples are calcium, magnesium, potassium, and gases such as oxygen and carbon dioxide.
When a cladogram splits into two different organisms or groups.
The phase that makes up the majority of the cell cycle. It prepares the cell for division and can be broken into three phases:Gap 1 (G1.), Synthesis (S), and Gap 2 (G2 ).
A type of asexual reproduction where a bud forms from the parent polyp's oral disk, producing same-sized polyps within the ring of tentacles.
An animal that does not have a spinal column or backbone.
An atom or molecule that has an electric charge, due to an unequal number of protons and electrons.
An organism whose influence on an ecosystem is larger than its abundance would suggest, often an apex predator.
A structure that forms on the centromere of a chromosome that is the point of attachment for microtubules during cell division.
A body of water that is separated from a larger body of water by a coral reef or land.
(Plural: larvae) A juvenile form of an organism that usually looks very different from the adult form.
The formal naming of organisms that includes the genus and species name. Also referred to as binomial nomenclature or scientific name.
(Singular: leaf) Represents the taxa in the study or the end of the ancestral lineage in a cladogram. This can be a group such as a phylum, or genus or it can be as specific as an individual species. Also referred to as tips or terminal node.
A series of events in an organism’s life, as it changes from one form to the next and eventually returns to its starting state.
Higher calcification rates due to greater light availability.
The amount of matter an object contains.
(Singular: spawner) A type of sexual reproduction when organisms, such as corals, release their gametes into the water at the same time. Also referred to as broadcast spawners and synchronous spawners.
A growth form that includes corals that look like domed boulders.
A physical substance that occupies space.
A body form of a cnidarian that is usually free swimming, is shaped like a bell (concave or convex), and possesses tentacles.
A type of cell division where one parent cell divides into four daughter cells with half (haploid) of the number of chromosomes as the parent cell.
(Singular: mesentery) Allow the stomach of a polyp to expand and also contain the reproductive cells.
Clear, jelly-like substance between the ectodermis and gastrodermis of a polyp. Helps maintain the form of the polyp.
The transformation when an organism develops from a juvenile to an adult.
An imaginary vertical plane that divides the cell into two halves during cell division.
The part of a scientific paper that demonstrates a systematic approach to studying science. This includes where, when, and how the research was conducted.
(Singular: microalga) Microscopic unicellular species of plants that can be found in freshwater or marine environments.
Miniature tubes that help to support the structure of the cell. It is like our skeleton and how it functions to support our body. They form spindle fibers during cell division.
A chain of continuous mountains that line each side of a rift valley.
A type of cell division when one parent cell divides to create two identical daughter cells. Each have their own nucleus and identical chromosomes.
When two or more atoms join together. For example, ozone (O3) is a molecule because it has more than one oxygen atom.
Located in the center of the oral disk of a polyp. This opening is used not only to inject food, but expel waste.
A gelatinous substance secreted by the ectodermis and used for protection, to aid in food capture, or to remove sediment and waste. Mucus is usually moved by cilia.
A type of symbiosis where both organisms benefit.
When an object does not float in a liquid.
Specialized stinging cells located in the ectodermis of the tentacles of a polyp that aid in predation.
A double layered membrane that surrounds the nucleus, separating the nucleus from the cytoplasm.
A type of symbiosis where organisms require the relationship to survive.
A fact that is learned through one of the five senses: sight, sound, touch, taste, and hearing.
Large geographic regions that are below sea level and contain many different features, such as abyssal plains, rift valleys, and plateaus.
The continuous movement of ocean water in a prevailing direction.
A layer of Earth's crust that forms the surface of the ocean basins.
A branch of science that studies the ocean.
(Singular: octocoral) A subclass of the class Anthozoa that is comprised of corals with eight-fold symmetry. Octocorals are soft corals.
An organism that feeds on both plants and animals.
A method that corals use to obtain zooxanthellae when corals retrieve zooxanthellae from the surrounding ocean waters.
An anatomical structure of a nematocyst that looks like a flap and whose pressure holds everything in place inside of the capsule.
The end of a coral containing the mouth.
Soft tissue between the mouth and surrounding tentacles that supports these structures.
An ecological level of organization that includes a single individual of one species.
A group on a cladogram that lies outside of the group being studied. It has less evolutionary relatedness to the other groups.
A type of symbiosis where one organism benefits and the other is harmed.
In cell division, the original cell that divides creating daughter cells.
A small, isolated coral reef that is often found in a lagoon or embayment. They are often circular in shape.
Measures if a solution is an acid or a base. The scale ranges from zero to fourteen. Seven is neutral. A pH of less than seven is acidic and a pH greater than seven is basic.
A growth form where each corallite has an individual wall. The corallite is tubular in shape and extends from a common base.
The process that plants or other organisms use to convert light energy into chemical energy. The chemical reaction equation is CO2 + H2O + energy → C6H12O6 + O2.
A diagram that is used to demonstrate evolutionary relationships among organisms. Also referred to as a cladogram or evolutionary tree.
The study of an organism’s evolutionary history.
Microscopic plant-like organisms that live in fresh and salt water environments. They make their own food through photosynthesis.
An individual coral outcrop that has a columnar shape that rises upward almost to the surface of the water.
An organism that feeds on fish.
An organism that feeds on plankton.
(Plural: planulae) The larval form of most cnidarians.
Elevated large, flat or nearly flat-topped tables that drop off abruptly on one or more sides.
An isolated reef, often found on top of underwater hills. They do not have a coral rim and are often crescent-shaped with a wide blanket of sediment behind it. Also referred to as a bank reef.
A growth form where corals form thin, plate-like structures. They growth horizontally and look like shelves.
A body form of a cnidarian that is cylindrical in shape with a mouth surrounded by tentacles.
An ecological level of organization that includes multiple organisms of the same species living in a defined area.
When an object floats to the surface of a liquid.
An organism in the food chain that feeds on autotrophs. They are usually herbivores.
Organisms that create their own food using light or chemical energy. Also referred to as an autotroph.
The molecules formed during a chemical reaction, found on the right side of the arrow.
(Singular: protozoon) A group of unicellular eukaryotic organisms, many of which are motile (can move).
An object that can evenly be divided around a central axis. Cnidarians are radially symmetrical.
The molecules that undergo a change in a chemical reaction, found on the left side of the arrow.
The highest point of a coral reef.
An area of a reef that is protected from wave action. It can extend for feet to miles (meters to kilometers) and the depth can range from inches to several feet (centimeters to a meter).
The area of a coral reef that is the furthest distance from shore and on the oceanic side of the reef crest. Also referred to as the fore reef.
A hand held tool used to measure salinity.
The process of creating offspring, either sexually or asexually.
A long, narrow, and often winding reef that develops parallel to the continental shelf.
An area where the seafloor is spreading forming large depressions in the deep ocean basin that are lined with mid-ocean ridges.
Ring of Fire
[rihng uhv fi-ur]
An area near margins of the Pacific Ocean where a large number of volcanic eruptions occur.
Safety in Numbers
[sayf-tee ihn nuhm-burz]
A group of organisms has less of a chance of being preyed on when there are more organisms present.
The amount of dissolved salt in a body of water. It is measured in parts per thousand (ppt).
The formal naming of organisms that includes the genus and species name. Also referred to as Latin name or binomial nomenclature.
(Singular: sclerite) Microscopic spicules (shards) composed of calcium or aragonite that help to support the structure of soft corals and anchor them to the substrate.
An underwater volcano.
An 8 inch (20.3 centimeter) round disk that has alternating black and white quadrants. This tool is used to measure turbidity.
An organism in the food chain that feeds on primary consumers. They are typically omnivores or carnivores.
Sand, fragments of rock, organic matter, and other small particles that can be carried by water and usually has settled to the bottom of the water column.
Sediment particles suspended in the water. Occurs when sediment is broken down by weathering and erosion and is transported by land or air to water sources such as rivers, oceans, and lakes.
(Singular: septum) Radial skeletal elements projecting inwards from the corallite wall that support the inner folds called the mesenteries.
Not able to move; immobile.
The production of a new living organism from two organisms of the opposite sex by the combination of sperm and eggs.
A trait that two lineages have in common.
(Singular: chromatid) Identical copies of a single chromosome.
The process when a lineage splits so two species arise from a common ancestor.
The structure that separates chromosomes during cell division. It contains the spindle fibers and centrosomes.
Clusters of microtubules that help to move chromosomes during cell division.
Spur and Groove Reef
A type of reef formation that extends seaward. Spurs refer to the areas that form parallel ridges of coral growth. They are separated by grooves that contain sediment and coral rubble.
Deep, steep-sided valleys that cut into the sea floor starting from the continental shelf to deep ocean basins.
The gradual sinking of land.
A surface where an organism can attach and/or grow.
The geographic region that extends from the Tropics of Cancer and Capricorn to 35° North and South latitudes.
Currents that occur at less than 300 feet (100 meters) deep. They are driven primarily by wind, tides, and waves.
The layer of water located above the thermocline. It is referred to as the mixed layer because this is where winds and waves stir up the water. This layer is also highly influenced by solar energy (from the sun) heating up the water. The temperature is roughly that of the air above it.
A close ecological relationship between the individuals of two (or more) different species.
(Singular: spawner) A type of sexual reproduction when organisms, such as corals, release their gametes into the water at the same time. Also referred to as broadcast spawners and mass spawners.
The second phase of interphase when DNA is replicated. Each chromosome gains an identical copy.
The study of biological diversity and its origins.
(Singular: taxon) A taxonomic group such as phylum, family, or species.
The science of classifying organisms.
The measure of how hot or cold something is. In physics, it’s defined as the measure of the kinetic energy of particles. It can be measured in Fahrenheit, Celsius, or Kelvins.
(Singular: tentacle) Feeding mechanism that surrounds the oral disk and aids in capturing prey.
Represents the taxa in the study or the end of the ancestral lineage in a cladogram. This can be a group such as a phylum or genus, or it can be as specific as an individual species. Also referred to as tips or leaves.
An organism in the food chain that feeds on secondary consumers. They are usually carnivores.
A pair of homologous chromosomes, with a total of four chromatids, that form during meiosis.
A layer of water located between the surface and deep water layers that rapidly decreases in temperature.
Large-scale ocean circulation that is driven by salinity and temperature. Often referred to as the global ocean conveyor belt.
The rope-like part of a nematocyst that can stick to, penetrate, or wrap itself around prey items.
(Singular: tip) Represents the taxa in the study or the end of the ancestral lineage in a cladogram. This can be a group such as a phylum or genus, or it can be as specific as an individual species. Also referred to as terminal node or leaves.
The study of the physical features and shape of the Earth.
The position that an organism occupies in a food chain or food web.
The geographic region that is located from the Tropic of Cancer in the northern hemisphere (23.4378° N) and extends to the Tropic of Capricorn in the southern hemisphere (23.4378° S).
A measure of the clarity of water. It can be caused by phytoplankton, sediments, runoff, pollution, etc.
A name given to an organism that is used for simplicity instead of the scientific name. Can vary depending on the geographic location and culture. Also referred to as the common name.
Seamounts that have risen above the ocean’s surface.
A measure of the amount of space an object takes up.
(Singular: coral) Corals that mainly thrive in subtropical and tropical latitudes where higher water temperatures exist.
Animal-like organism that lives in aquatic environments. For some, this is the larval form of animals such as sea urchins, coral, crabs, worms, etc.
(Singular: zooxanthella) A yellow-brown symbiotic algae that lives in the tissues of corals and other marine invertebrates.
A fertilized egg.