A body plan is a group of structural and developmental characteristics that can be used to identify a group of animals, such as a phylum. All members of a particular group share the same body plan at some point during their development—in the embryonic, larval, or adult stage. Skip to content What is Aboral surface?
What is the oral surface? What is another name for the Aboral surface of a starfish? Is Aboral a word? What is the Aboral end? What is the purpose of madreporite? What are the three types of body plans? How can you differentiate between the oral and Aboral side of a sea star? What is the meaning of radially symmetrical? Whats the meaning of adorable? This five-sided radial structure of echinoderms makes the body strong Fig. A five-sided skeleton is stronger than a four- or six-sided one because the line of weakness cannot run directly across the body.
Even a three-sided body plan is weaker than a five-sided one. Most animals that move around have bilateral symmetry, as described in the previous sections on molluscs, worms, and arthropods. But echinoderms, although they also move, are radially symmetrical, so the terms anterior , posterior , dorsal , and ventral do not apply.
In the echinoderms there are two surfaces. One is the oral surface, where the mouth is and the tube feet project.
The tube feet on the oral surface are limited to distinct regions called the ambulacral regions. The other surface is the aboral , which typically contains the anal opening of the digestive system. All echinoderms are variations on this oral-aboral body plan Fig. Sea stars class Asteroidea and brittle stars class Ophiuroidea have flat bodies with a broad aboral surface facing up and an oral surface facing down.
Both groups have arms projecting from a central body disc and the ambulacral regions with the projecting tube feet extending along each of the arms Fig. Like sea stars, the feather stars and sea lilies class Crinoidea have arms, but the oral surface faces up, away from the bottom Fig.
The tube feet extend upward from the oral surface to capture particles of food floating by. Feather stars grasp the substrate with a series of rootlike projections from the aboral surface and sea lilies have long, stalk-like projections from the aboral surface with which they permanently attach themselves to the bottom. Sea urchins class Echinoidea have no arms Fig. The radial body plan is spherical. The oral surface, with ambulacral regions and tube feet, covers most of the sphere.
The aboral surface is only a small disc at the top. In most sea urchins, spines also extend from the oral surface, usually between the rows of tube feet.
The radial body plan of sea cucumbers class Holothuroidea is tube-shaped, with the aboral surface just a small region at the end opposite the mouth Fig. Most of the long body is covered by the oral surface, with tube feet projecting in five rows. Many of the tube feet around the mouth take the form of long tentacles, used for gathering food.
The body lies on its side, giving the appearance of bilateral symmetry. The tube feet touching the bottom usually bear suction cups and are used for locomotion.
All echinoderms also lack any kind of central nervous system or brain, but have a nerve ring. Echinoderms also have calcium carbonate endoskeletons, ranging from microscopic spicules in sea cucumbers to visible plates in sea stars and urchins.
Most echinoderms have a complete digestive system and a large coelom. They have separate sexes, usually with gonads in sets of five, showing internal pentaradial symmetry.
All echinoderm species live in the ocean; there are no freshwater or terrestrial echinoderms. Sea urchins Fig. Sea urchins are relatively small; most species could fit in the palm of your hand. The spines are adaptations that protect the urchins from predators. Spines and tube feet help urchins move and get food. The long, thin, sharp spines of some sea urchins easily penetrate flesh and in some species, toxic chemicals on the tissue covering the sharp spines make its stab extremely painful Fig.
Other species, with short, thick, or blunt spines are safe to handle Fig. A few species that have adapted to live in the wave surge zone of rocky coastlines have flattened spines Fig. Flat, broad plate spines give these urchins a low profile and prevent them from getting swept away by powerful waves. Sand dollars have fine velvet-textured spines that help these animals burrow into sand Fig.
Pedicellariae are small jaw-like pincher appendages found on many species of sea urchins and sea stars Fig. They are typically attached to the echinoderm body at the base of the spines.
The name pedicellaria comes from the Latin root words ped - meaning foot and - icellus meaning little. A pedicellaria snaps open if something touches its outer surface; it snaps shut if it is touched on its inner surface. Some pedicellariae are toxic, containing a small poison gland. Others have powerful jaws that can crush small organisms. The soft inner organs of sea urchins are protected by a hard structure called a test.
An urchin test is a hard internal skeleton composed of calcium carbonate CaCO 3 plates Fig. The plates interlock in a tight geometric pattern that makes the skeleton rigid. Because the test is covered by very thin skin or epidermis, it is considered to be an endoskeleton. They have many different adaptations, depending on their habitat. Most are arboreal.
Others, like macaques, baboons, and some mangabeys, are more terrestrial. All monkeys can use their hands and feet for holding on to branches, but some arboreal monkeys can use their tails, too. Aquatic animals may breathe air or extract oxygen that dissolved in water through specialised organs called gills, or directly through the skin.
Natural environments and the animals that live in them can be categorized as aquatic water or terrestrial land. Aerial animals are basically any animal who can naturally fly, glide, or soar in the air. Aerial animals include birds, insects, bats, sugar gliders, flying squirrels, and many others! What is Aboral surface? Category: pets fish and aquariums. In biology, aboral surfaces are surfaces away from or opposite the mouth.
It is also the opposite of oral which is the end containing the mouth of a radially symmetrical animal. What is the difference between oral and Aboral?
What does oral directions mean? What is the largest echinoderm class? What does Ambulacral mean? Skin gills are thin-walled extensions of the coelom through the body wall and are respiratory structures. The skin gills are muscular and can be retracted into the surface of the body wall and may be retracted and inconspicuous in preserved specimens. The anus is located near the center of the aboral surface but is almost impossible to demonstrate externally. Turn the animal over and study the oral surface.
Find the large mouth in the center of the disk, surrounded by the thin peristomial membrane. The yellowish-orange curtain-like folds of the cardiac stomach may be visible inside the mouth. Five deep ambulacral grooves radiate outward from the mouth, one along the midline of the oral surface of each arm. The numerous soft, tubular structures projecting into the groove from either side are the tube feet , or podia.
Two rows of tube feet are present on each side of the groove. The tube feet of Asterias bear suckers at their distal ends. Note the rows of long, flattened movable spines on each side of the ambulacral groove. The word ambulacrum is Latin for "covered way," an apt name as these spines are used to cover the groove to protect the tube feet. Look at the tip of one of the arms. As is usual in radially symmetrical animals, the sensory structures are arrayed around the periphery, which in sea stars are the tips of the arms.
Several long, narrow sensory tube feet with chemo- and mechanoreceptors extend from the tip of each arm. These are easily seen in living specimens but contract and become inconspicuous in preserved material. At the tip of the arm is a small circle of short, blunt movable spines that are not associated with pedicellariae.
These spines surround a small, pale red or yellow eyespot. The eyespot is on the oral surface of the arm, almost at the tip.
Slides of early starfish developmental stages may be available in the laboratory. These may include all early developmental stages on a single side or on separate slides. Many of the stages are spheres which must be distinguished from each other using various clues. Keep in mind as you interpret the embryos that they are whole mounts, not sections, and their appearance will vary depending on the level of your plane of focus optical section.
First in the developmental series is the unfertilized female gamete, the egg , or ovum. The plasma membrane is the outer boundary of the cell and, since the egg has not been fertilized, there is no fertilization membrane. Once fertilized, the egg becomes a zygote. This stage is also a sphere but a wrinkled, transparent fertilization membrane is present around the cell. The fertilization membrane is produced immediately after fertilization and prevents penetration by additional sperm.
The zygote is the same size as the ovum. Starfish early development. Ovum, B. Zygote, C. Polar view of 4-celled embryo, E. Polar view of 8-celled embryo, F. Early blastula, G. Late blastula, H. Early gastrula. Search the side for examples early cleavage stages, namely 2-cell, 4-cell, and 8-cell embryos, each enclosed in a fertilization membrane. Pay attention to the orientation of the blastomeres with respect to each other, especially those of the 8-cell stage.
Observe an 8-cell embryo and verify that the cell arrangement is typical of radially cleaving embryos. One of the tasks accomplished by early development is conversion of the enormous ovum to a multitude of much smaller cells, closer in size to normal somatic cells. The embryo does not grow during this period so, since cells are dividing, they must be getting smaller. Subsequent divisions produce ever smaller cells, which are arrayed in a hollow ball known as a blastula.
The blastula is ciliated and if these embryos were alive you could see them rotating inside their fertilization membranes. As divisions continue the cells in the blastula wall get smaller and smaller until they can no longer be distinguished from each other. You can, however, still see the blastocoel in the center and the wall of cells enclosing it.
The embryo is still about the same size as the original ovum but its cells are much smaller. Eventually one end of the blastula thickens in preparation for gastrulation.
This end then invaginates to form a double walled embryo known as a gastrula. The early gastrula has only a short invagination but it will rapidly increase in size and you should be able to find examples of several ages.
The blastocoel remains but there is now a second cavity, the archenteron, or embryonic gut. The archenteron opens to the exterior by an opening, the blastopore. The asteroid gastrula develops into a series of two larvae, the first of which is the bipinnaria larva , followed by the brachiolaria larva. The larvae are ciliated and feed on diatoms in the plankton. Once the embryo begins feeding it can start to grow.
The larvae are bilaterally symmetrical. Several examples of bipinnaria larvae should be present on the slide. The bipinnaria larva has one or two locomotor ciliary bands. Young larvae have only one band but older larvae have two.
0コメント