The Phylum Echinodermata is made up of the most advanced invertebrates and includes organisms such as the starfish, sea urchins and sea cucumbers. Echinoderm habitat is exclusively marine. The word echinoderm means spiny skin (echino = spiny, derm = skin) which is fitting; their endoskeleton is composed of calcium-based plates called ossicles that are covered by a thin skin.
Echinoderms display 5-part radial (or pentaradial) symmetry as adults. They can be herbivores or predators. If sea stars or sea urchins lose a body part to a predator, they are able to regenerate those parts.
This sea star is regenerating two of its arms.
A unique feature of all echinoderms is their water vascular system; these interconnected tubes allow them to move, feed and exchange gases (respiration).
Starfish use their tube feet to sense their environment, to move and to pry open prey (clams, mussels). Some may even extrude their stomachs into their prey to digest them.
Echinoderms, like chordates, are deuterostomes in which the blastopore (first opening in embryo) becomes the anus. All other invertebrates are protostomes, in which the blastopore in their development becomes the mouth.
Watch the following movie clip from The Shape of Life to learn more about the Echinoderms. While viewing, record important ideas on your Fact Sheet.
A review of some general features of all Echinoderms:
- No cephalization or brain, but they do have a nerve ring to coordinate movements in muscles between ossicles.
- The water vascular system is made up of a system of canals; they help the organism feed and move. Water enters through an opening called the madreporite into a short stone canal into the ring canal. Radial canals connect to the ring canal and determine the five-part symmetry. This hydraulic water system is strong enough to help starfish open clam shells.
- They can reproduce asexually by fragmentation or sexually with external fertilization.
Look at this picture to view the diversity and classification of the Phylum Echinodermata.
Look at the animals above. Which would you say are chordates? Hover over the image to check your answer!
The Chordates represent a diverse group of organisms that range from the tunicates to vertebrates (fish, amphibians, reptiles, birds, mammals). They are all bilaterally symmetrical and display the following 4 characteristics at some point in their lifetime.
- Notochord : A firm, flexible rod of specialized cells that becomes the endoskeleton in vertebrates.
- Dorsal nerve cord : A hollow tube above the notochord that becomes the spinal cord and brain in vertebrates.
- Pharyngeal pouches : Out-pockets in the pharynx, the portion of the digestive tract between the mouth and the esophagus.
- Become gill chambers and gills in aquatic environments.
- Become jaws, inner ear, and tonsils in terrestrial chordates.
- Post-anal tail: A tail located posterior to the anal opening.
Phylum Chordata consists of three subphyla pictured below. The only subphylum with Vertebrate members is the Craniata. Roll your mouse over each group to learn more.
Watch the following movie clip from The Shape of Life to learn more about the Chordates. While viewing, record important ideas on your Animal Phyla Fact Sheet.
Two Vertebrate Advances: Endothermy and the Amniotic Egg
Up to this point, all of the animals we have discussed have been ectotherms. An ectotherm is an organism that cannot regulate its own body temperature and must rely upon external sources of temperature for their metabolic rate. Lizards, for instance, are ectotherms and must bask in the sun or at a heat source to increase their internal temperature and activity. Sometimes these organisms are called “cold-blooded.”
We will see that some of the Vertebrates have developed the adaptation of endothermy. An endotherm is an organism that has the ability to regulate its body temperature independent of the environment. Endotherms, such as mammals, are able to increase and regulate their temperature internally by metabolic processes. Sometimes these organisms are called “warm-blooded.”
Endothermy is advantageous because it allows those animals the ability to maintain an optimum temperature for enzyme function. Endotherms live in environments with daily or seasonal temperature fluctuation. Endotherms can be active at night or in colder ecosystems. However, the price they pay is an increased need for energy (food)!
Amniotes are organisms whose fertilized offspring, the amniotic egg, are protected within the female or laid on dry land. Amniotes include reptiles, birds and mammals. The egg protects the embryo from disease, drying out, and damage while development is occurring. The inside of the egg is a watery environment rich in oxygen (it enters through the pores in the shell). The amniotic egg was a key evolutionary step in moving animals from water onto land.
Birds and reptiles lay eggs, but most mammals’ eggs lack a shell and have evolved to grow within the mother’s womb. The platypus is an example of an exception to this rule: it is a mammal that lays eggs.
The amniotic egg, such as this fertilized chicken egg, is equipped with protection and nutrition for the growing embryo (red). Hens can lay fertilized eggs after mating with a rooster, and lay eggs that have not been fertilized. The eggs we purchase from the store are unfertilized.
The Vertebrates: Chordates With Backbones
Within the Craniata are the Vertebrates, which include fish, amphibians, reptiles, birds, and animals. Vertebrates have a number of features that make them successful:
- Endoskeleton with backbone (spinal cord protected by vertebrae)
- Cephalization with skull for protection
- Complex brains
- Sense organs
- Organ systems present
- Closed circulatory system, chambered heart
- Endo- or Ectothermic
- Bilateral symmetry
- Two pairs of jointed appendages (limbs, fins)
Vertebrates can be further subdivided into the fish and the tetrapods, which have four limbs:
- Class Agnatha (jawless fish)
- Class Chondrichthyes (cartilaginous fish)
- Class Osteichthyes (bony fish)
- Class Amphibia (amphibians)Class Reptilia (reptiles)
- Class Aves (birds)
- Class Mammalia (mammals)