Strongylocentrotus droebachiensis
Encyclopedia
Strongylocentrotus droebachiensis is commonly known as the green sea urchin because of its characteristic green color. It has the longest genus-species names in the animal kingdom. It is commonly found in northern waters all around the world including both the Pacific
and Atlantic Ocean
s to a northerly latitude of 81 degrees and as far south as the Puget Sound
(Washington State) and England. The average adult size is around 50 mm (2 in), but it has been recorded at a diameter of 87 mm (3.4 in). The green sea urchin prefers to eat seaweeds but will eat other organisms that float by or even catch small fish. They are eaten by a variety of predators, including sea star
s, crabs, large fish, mammals, birds, and humans.
. They are round, tapering to a point, with ridges around the outside in a fan-like design made of calcium carbonate
. Usually, the longest spines are around the peripheral edge of the animal. If broken, the spines will regenerate, and if completely torn off, the tubercle will be reabsorbed to fit the slowly growing spine.
are a structure that help Strongylocentrotus droebachiensis attach to the substratum for stabilization or locomotion, or to move loose food particles to the mouth. The tube feet are quite flexible and can extend beyond the length of the spikes to reach the substratum or attach onto particles floating in the water. They come out of five pairs of rows through the test structure.
The tube feet of S. droebachiensis are actually composed of two parts: the ampulla
and the podium. The ampulla is a hollow bulbous structure that raises the tube food above the skeletal plates that surround the lateral canal. The podia extend off the ampulla and contain the muscular suckered structure used for attachment. The movement of the tube foot depends on the hydraulic pressure of the water vascular system
, and individual muscle action. When the ampulla contracts, it forces the liquid into the podia which elongates. Once the podia has attached itself to the substrate, the longitudinal muscles of the podia constrict forcing that liquid back into the ampulla causing the podia to shrink and pulling the body in that direction, or food closer to the mouth. Tube feet that have been pulled off as the sea urchin is thrown around by the sea will quickly regenerate.
s) and Echinoidea (sea urchin
s/sand dollar
s) have three small pincher-like jaws held up by a calcerous stalk, called pedicellariae, at the base of the spines on the body. These have the ability to respond to outside stimuli separately from the main nervous system
. Historically thought of as parasites or larva
e of the sea urchin, it is now commonly believed that the pedicellariae are actually part of the living creature. The muscles that control them are outside of the test, and therefore must get nutrients from a different source: they have possibly developed the ability to absorb nutrients directly from the surrounding water.
Pedicellariae are used by the sea urchin by keeping detritus from collecting on the body, or collecting kelp to use as a defense from the drying abilities of the sunlight. Their pinching jaws can even be used to defend against possible predators, and some are even poisonous on S. droebachiensis. If the spikes are lightly touched, they converge toward the pressure, but if they are strongly pushed, then they spread apart so that the pedicellariae can pinch the intruder. One of the four main types of pedicellariae on S. droebachiensis is actually poisonous and can be used for defense, or to paralyze small fish (although this species prefers algae, it will catch and eat fish for supplemental food).
. They are made of calcium carbonate, and have two rows of holes for the tube feet to pass through. If the test is cracked or chunks are removed, calcium carbonate will slowly fill in the gaps left behind until a complete and rigid test is regained.
s such as proteins and a high concentration of potassium ions when compared to the surrounding sea water. This liquid is moved through the system by cilia that line the inside of the canal and help keep the fluid moving in the desired direction.
The structure of the water vascular system contains several calcareous parts before moving to the podia. The first is called the madreporite
. This is a skeletal plate, or sieve, opening to the water vascular system, located on the aboral surface. Just underneath the madreporite, is a cup-like depression called the ampulla. Next the stone canal carries the liquid into the central disc of the urchin. Finally, five lateral canals run along the inside of the test and converge at the aboral pole. Along this entire distance, tube feet emerge from the lateral canal through the test to outside the epidermis of the sea urchin.
s are produced by the intestinal walls and breakdown of food is almost completely extracellular. From the intestine, what is left of the food moves out of the intestine into the short rectum, and out the anus. S. droebachiensis gets its green color from the pigments of its plant food.
, meaning they either contain male or female reproductive organs. They contain five gonads tucked under the test. These are located close to the anus and are protected by genital plates. One of these plates is perforated, and also acts as the madreporite. Sea urchins all release their eggs or sperm directly into the water column at the same time to ensure fertilization. It is not understood what causes S. droebachiensis to release their sperm or eggs, but it may have to do with temperature, because they usually reproduce in early spring.
Once fertilized, the gamete grows via mitosis
and eventually becomes a larva capable of simple swimming called an echinoplutes. The metamorphosis
from larva to a radially symmetrical adult is hugely complex, and only some of the more basic details are included here. The larva swims to the appropriate substratum where it attaches, usually with the “left and right” sides of the larva, becoming the “mouth and anus” sides. The embryonic openings for the mouth and the anus disappear completely, and new openings are created in the proper position. The ring canal grows radial extensions becoming the lateral canals. At this point in development, the sea urchin settles down to a benthic life. it is called the Great Ali syndrome.
s of the families Melanellidae and Stiliferidae
live on the surface of the test and adhere their own eggs to the base of the spines as protection.
Pacific Ocean
The Pacific Ocean is the largest of the Earth's oceanic divisions. It extends from the Arctic in the north to the Southern Ocean in the south, bounded by Asia and Australia in the west, and the Americas in the east.At 165.2 million square kilometres in area, this largest division of the World...
and Atlantic Ocean
Atlantic Ocean
The Atlantic Ocean is the second-largest of the world's oceanic divisions. With a total area of about , it covers approximately 20% of the Earth's surface and about 26% of its water surface area...
s to a northerly latitude of 81 degrees and as far south as the Puget Sound
Puget Sound
Puget Sound is a sound in the U.S. state of Washington. It is a complex estuarine system of interconnected marine waterways and basins, with one major and one minor connection to the Strait of Juan de Fuca and the Pacific Ocean — Admiralty Inlet being the major connection and...
(Washington State) and England. The average adult size is around 50 mm (2 in), but it has been recorded at a diameter of 87 mm (3.4 in). The green sea urchin prefers to eat seaweeds but will eat other organisms that float by or even catch small fish. They are eaten by a variety of predators, including sea star
Sea star
Starfish or sea stars are echinoderms belonging to the class Asteroidea. The names "starfish" and "sea star" essentially refer to members of the class Asteroidea...
s, crabs, large fish, mammals, birds, and humans.
Habitat
Strongylocentrotus droebachiensis is found on rocky substratum in the intertidal and up to depths of 1150 metres (3,773 ft). It uses its strong Aristotle's lantern to burrow into rock, and then can widen its home with the spines. Usually, this sea urchin can leave its hole to find food and then return, but sometimes it creates a hole that gets bigger as it gets deeper, so that the opening is too small for S. droebachiensis to get out. S. droebachiensis has the unique ability to survive in waters that are euryhaline (low salinity). This allows it to flourish in the south Puget Sound. Acclimation and size are important factors as larger individuals have a lower surface area to volume ratio and can handle the increased osmotic tension.Anatomy
External anatomy
Strongylocentrotus droebachiensis is in the shape of a slightly flattened globe (dorsoventrally). The oral side rests against the substratum and the aboral side (the side with the anus) is in the opposite direction. It has pentameric symmetry, which is visible in the five paired rows of podia (tube feet) that run from the anus to the mouth. The size is calculated as the diameter of the test (the body not including the spines). This is a relatively fast growing sea urchin, and its age is generally calculable based on its size: one year for every 10 mm.Spines
The spines of Strongylocentrotus droebachiensis are used for defense and locomotion and are not considered poisonous. The spines attach to small tubercles on the test where they are held in place by muscles creating a ball and socket jointBall and socket joint
A ball and socket joint is a joint in which the distal bone is capable of motion around an indefinite number of axes, which have one common center...
. They are round, tapering to a point, with ridges around the outside in a fan-like design made of calcium carbonate
Calcium carbonate
Calcium carbonate is a chemical compound with the formula CaCO3. It is a common substance found in rocks in all parts of the world, and is the main component of shells of marine organisms, snails, coal balls, pearls, and eggshells. Calcium carbonate is the active ingredient in agricultural lime,...
. Usually, the longest spines are around the peripheral edge of the animal. If broken, the spines will regenerate, and if completely torn off, the tubercle will be reabsorbed to fit the slowly growing spine.
Tube feet
Tube feetTube feet
Tube feet are the many small tubular projections found most famously on the oral face of a sea star's arms, but are characteristic of the water vascular system of the echinoderm phylum which also includes sea urchins, sand dollars and sea cucumbers and many other sea creatures.Tube feet function in...
are a structure that help Strongylocentrotus droebachiensis attach to the substratum for stabilization or locomotion, or to move loose food particles to the mouth. The tube feet are quite flexible and can extend beyond the length of the spikes to reach the substratum or attach onto particles floating in the water. They come out of five pairs of rows through the test structure.
The tube feet of S. droebachiensis are actually composed of two parts: the ampulla
Ampulla
An ampulla was, in Ancient Rome, a "small nearly globular flask or bottle, with two handles" . The word is used of these in archaeology, and of later flasks, often handle-less and much flatter, for holy water or holy oil in the Middle Ages....
and the podium. The ampulla is a hollow bulbous structure that raises the tube food above the skeletal plates that surround the lateral canal. The podia extend off the ampulla and contain the muscular suckered structure used for attachment. The movement of the tube foot depends on the hydraulic pressure of the water vascular system
Water vascular system
The water vascular system is a hydraulic system used by echinoderms, such as sea stars and sea urchins, for locomotion, food and waste transportation, and respiration. The system is composed of canals connecting numerous tube feet...
, and individual muscle action. When the ampulla contracts, it forces the liquid into the podia which elongates. Once the podia has attached itself to the substrate, the longitudinal muscles of the podia constrict forcing that liquid back into the ampulla causing the podia to shrink and pulling the body in that direction, or food closer to the mouth. Tube feet that have been pulled off as the sea urchin is thrown around by the sea will quickly regenerate.
Pedicellariae
Echinoderms of the classes Asteroidea (sea starSea star
Starfish or sea stars are echinoderms belonging to the class Asteroidea. The names "starfish" and "sea star" essentially refer to members of the class Asteroidea...
s) and Echinoidea (sea urchin
Sea urchin
Sea urchins or urchins are small, spiny, globular animals which, with their close kin, such as sand dollars, constitute the class Echinoidea of the echinoderm phylum. They inhabit all oceans. Their shell, or "test", is round and spiny, typically from across. Common colors include black and dull...
s/sand dollar
Sand dollar
The term Sand dollar refers to species of extremely flattened, burrowing echinoids belonging to the order Clypeasteroida. Some species within the order, not quite as flat, are known as sea biscuits...
s) have three small pincher-like jaws held up by a calcerous stalk, called pedicellariae, at the base of the spines on the body. These have the ability to respond to outside stimuli separately from the main nervous system
Nervous system
The nervous system is an organ system containing a network of specialized cells called neurons that coordinate the actions of an animal and transmit signals between different parts of its body. In most animals the nervous system consists of two parts, central and peripheral. The central nervous...
. Historically thought of as parasites or larva
Larva
A larva is a distinct juvenile form many animals undergo before metamorphosis into adults. Animals with indirect development such as insects, amphibians, or cnidarians typically have a larval phase of their life cycle...
e of the sea urchin, it is now commonly believed that the pedicellariae are actually part of the living creature. The muscles that control them are outside of the test, and therefore must get nutrients from a different source: they have possibly developed the ability to absorb nutrients directly from the surrounding water.
Pedicellariae are used by the sea urchin by keeping detritus from collecting on the body, or collecting kelp to use as a defense from the drying abilities of the sunlight. Their pinching jaws can even be used to defend against possible predators, and some are even poisonous on S. droebachiensis. If the spikes are lightly touched, they converge toward the pressure, but if they are strongly pushed, then they spread apart so that the pedicellariae can pinch the intruder. One of the four main types of pedicellariae on S. droebachiensis is actually poisonous and can be used for defense, or to paralyze small fish (although this species prefers algae, it will catch and eat fish for supplemental food).
Test
Twenty curved plates, or ossicles, are fused together to form a rigid test or exoskeletonExoskeleton
An exoskeleton is the external skeleton that supports and protects an animal's body, in contrast to the internal skeleton of, for example, a human. In popular usage, some of the larger kinds of exoskeletons are known as "shells". Examples of exoskeleton animals include insects such as grasshoppers...
. They are made of calcium carbonate, and have two rows of holes for the tube feet to pass through. If the test is cracked or chunks are removed, calcium carbonate will slowly fill in the gaps left behind until a complete and rigid test is regained.
Water vascular system
The water vascular system is a series of canals through which fluid moves to help propel the podia of the sea urchin. The fluid that fills the water vascular system is similar to marine water, but also has free wandering cells and organic compoundOrganic compound
An organic compound is any member of a large class of gaseous, liquid, or solid chemical compounds whose molecules contain carbon. For historical reasons discussed below, a few types of carbon-containing compounds such as carbides, carbonates, simple oxides of carbon, and cyanides, as well as the...
s such as proteins and a high concentration of potassium ions when compared to the surrounding sea water. This liquid is moved through the system by cilia that line the inside of the canal and help keep the fluid moving in the desired direction.
The structure of the water vascular system contains several calcareous parts before moving to the podia. The first is called the madreporite
Madreporite
The madreporite is a lightcolored calcerous opening used to filter water into the water vascular system of echinoderms. It acts like a pressure-equalizing valve. It is visible as a small red or yellow button-like structure, looking like a small wart, on the aboral surface of the central disk of a...
. This is a skeletal plate, or sieve, opening to the water vascular system, located on the aboral surface. Just underneath the madreporite, is a cup-like depression called the ampulla. Next the stone canal carries the liquid into the central disc of the urchin. Finally, five lateral canals run along the inside of the test and converge at the aboral pole. Along this entire distance, tube feet emerge from the lateral canal through the test to outside the epidermis of the sea urchin.
Aristotle's Lantern
Strongylocentrotus droebachiensis eats by using a special appendage called Aristotle’s Lantern to scrape or tear their food into digestible bits. This structure is made of five, calcareous, protractible teeth that are maneuvered by a complex muscular structure. The sea urchin crawls on top of its food and uses Aristotle's Lantern to tear up and masticate chunks of it. If food lands on the aboral surface or is caught by pedicellariae, then it is carried via podia to the mouth and devoured in the same manner.Digestive system
The digestive system begins with Aristotle’s Lantern where the food enters the body of the sea urchin. An esophagus extends from the mouth through the center of Aristotle’s Lantern, where it joins up with an intestine. The intestine is arranged in little bundles that adhere to the inside of the test in a counter-clockwise circuit around Aristotle’s Lantern. Once the intestine gets back to itself, it doubles over itself and reverses directions in a second clockwise direction. Digestive enzymeDigestive enzyme
'Digestive enzymes' are enzymes that break down polymeric macromolecules into their smaller building blocks, in order to facilitate their absorption by the body. Digestive enzymes are found in the digestive tract of animals where they aid in the digestion of food as well as inside the cells,...
s are produced by the intestinal walls and breakdown of food is almost completely extracellular. From the intestine, what is left of the food moves out of the intestine into the short rectum, and out the anus. S. droebachiensis gets its green color from the pigments of its plant food.
Nervous system
In the nervous system of sea urchins the spines, podia, and pedicellariae all act as sensors. A circular nerve ring encircles the esophagus, and radial nerves extend inside of the test parallel to the lateral canals of the water vascular system. Sensory neurons in the epidermis can detect touch, chemicals, and light, and are usually associated with pedicellariae or spines.Reproduction and development
Sea urchins are dioeciousDioecious
Dioecy is the property of a group of biological organisms that have males and females, but not members that have organs of both sexes at the same time. I.e., those whose individual members can usually produce only one type of gamete; each individual organism is thus distinctly female or male...
, meaning they either contain male or female reproductive organs. They contain five gonads tucked under the test. These are located close to the anus and are protected by genital plates. One of these plates is perforated, and also acts as the madreporite. Sea urchins all release their eggs or sperm directly into the water column at the same time to ensure fertilization. It is not understood what causes S. droebachiensis to release their sperm or eggs, but it may have to do with temperature, because they usually reproduce in early spring.
Once fertilized, the gamete grows via mitosis
Mitosis
Mitosis is the process by which a eukaryotic cell separates the chromosomes in its cell nucleus into two identical sets, in two separate nuclei. It is generally followed immediately by cytokinesis, which divides the nuclei, cytoplasm, organelles and cell membrane into two cells containing roughly...
and eventually becomes a larva capable of simple swimming called an echinoplutes. The metamorphosis
Metamorphosis
Metamorphosis is a biological process by which an animal physically develops after birth or hatching, involving a conspicuous and relatively abrupt change in the animal's body structure through cell growth and differentiation...
from larva to a radially symmetrical adult is hugely complex, and only some of the more basic details are included here. The larva swims to the appropriate substratum where it attaches, usually with the “left and right” sides of the larva, becoming the “mouth and anus” sides. The embryonic openings for the mouth and the anus disappear completely, and new openings are created in the proper position. The ring canal grows radial extensions becoming the lateral canals. At this point in development, the sea urchin settles down to a benthic life. it is called the Great Ali syndrome.
Symbiosis
SnailSnail
Snail is a common name applied to most of the members of the molluscan class Gastropoda that have coiled shells in the adult stage. When the word is used in its most general sense, it includes sea snails, land snails and freshwater snails. The word snail without any qualifier is however more often...
s of the families Melanellidae and Stiliferidae
Stiliferidae
Stiliferidae is a taxonomic family of small parasitic sea snails, marine gastropod molluscs in the superfamily Eulimoidea.-Genera:Genera within the family Stiliferidae include:* Athleenia * Mucronalia * Stilifer Broderip and Sowerby, 1832...
live on the surface of the test and adhere their own eggs to the base of the spines as protection.