An interesting feature of these animals is their power to regenerate, even when over 75 percent of their body mass is lost. Echinoderms possess a unique ambulacral or water vascular system, consisting of a central ring canal and radial canals that extend along each arm. Water circulates through these structures and facilitates gaseous exchange as well as nutrition, predation, and locomotion. The water vascular system also projects from holes in the skeleton in the form of tube feet.
These tube feet can expand or contract based on the volume of water present in the system of that arm. By using hydrostatic pressure, the animal can either protrude or retract the tube feet. Water enters the madreporite on the aboral side of the echinoderm. From there, it passes into the stone canal, which moves water into the ring canal. The ring canal connects the radial canals there are five in a pentaradial animal , and the radial canals move water into the ampullae, which have tube feet through which the water moves.
By moving water through the unique water vascular system, the echinoderm can move and force open mollusk shells during feeding. The nervous system in these animals is a relatively simple structure with a nerve ring at the center and five radial nerves extending outward along the arms.
Structures analogous to a brain or derived from fusion of ganglia are not present in these animals. Podocytes, cells specialized for ultrafiltration of bodily fluids, are present near the center of echinoderms. These podocytes are connected by an internal system of canals to an opening called the madreporite.
Echinoderms are sexually dimorphic and release their eggs and sperm cells into water; fertilization is external. In some species, the larvae divide asexually and multiply before they reach sexual maturity. Echinoderms may also reproduce asexually, as well as regenerate body parts lost in trauma.
This phylum is divided into five extant classes: Asteroidea sea stars , Ophiuroidea brittle stars , Echinoidea sea urchins and sand dollars , Crinoidea sea lilies or feather stars , and Holothuroidea sea cucumbers Figure 2.
Sea lilies are an ancient group, going back about mya. They were thought to be extinct until they were rediscovered growing on the ocean floor. In sea lilies, the mouth and anus are both on the upper surface on a small disc, with the arms located along the edge of the disc. Crinoid tube feet are modified for filter feeding. How does the radial symmetry of echinoderms relate to their life style? Aren't all higher animals bilaterally symmetric?
We now turn to the last phylum of animals, one that dominates the deuterostomes as thoroughly as arthropods dominate the protostomes, the Phylum Chordata 42, sp. Chordates are eucoelomate deuterostomes , and probably share a common ancestor with echinoderms. Three important characteristics unite the Phylum Chordata. At some point in their life cycle, all chordates have a notochord , a dorsal hollow nerve cord , and pharyngeal gill slits. A notochord is a flexible supporting rod of cartilage, although in most adult chordates the notochord is replaced by a vertebral column.
The dorsal hollow nerve cord ultimately forms the spinal cord and the brain. The pharyngeal gill slits appear in all chordate embryos, an echo of our distant origin in the sea, but are usually lost in the early development of the organism.
Primitive chordates evolved small slits opening into the pharynx. By contracting the pharynx, the animal could draw water into its body and over the gill slits. These slits originally functioned in aiding respiration and capturing food by filter feeding. Smaller, more primitive vertebrates could rely on diffusion for gas exchange, but larger and more active forms required more surface area to allow rapid exchange of gases. Chordates evolved gills , sheets of highly folded tissue in the spaces between the gill slits, tissues with a very rich blood supply to exchange gases.
Gill arches were reinforced with cartilage to help hold them open. Over time, the area between the gills, or the gill arches, became ossified turned harder and migrated slightly forward to form the first primitive vertebrate jaw. Vertebrates could now bite and chew their prey, and were no longer limited to filter feeding as a way of life. Class Mammalia - placental humans , marsupial kangaroo , monotremes egg layers - platypus. Phylum Chaetognatha - sp. I doubt if anyone here has ever noticed one of these worms while swimming in the ocean.
These tiny little predators are only cm. But they are incredibly abundant. They are the most abundant carnivore in the ocean. They are the tiger sharks of the plankton. The tiny moveable hooks that surround the mouth, and give these creatures their name, are used to capture prey.
Prey are injected with a tiny jolt of tetrodotoxin , the same paralytic poison found in some Japanese puffer fish. They lack circulatory, respiratory and excretory organs, relying entirely on diffusion. They are living fossils, going back essentially unchanged for about my. They represent a very early branch on the chordate tree. These marine worms are another ancient group, evolving about mya. They may be the first deuterostomes on Earth.
They range in size from 2 cm to 1. They share some of the fundamental characteristics of the chordates, which we'll review later, such as a dorsal hollow nerve cord and gill slits.
We used to think they also had a notochord, another chordate trademark, but closer study revealed this hypothesis to be wishful thinking. They live in U-shaped burrows in the ocean floor. Notice the slits in the side of the pharynx. These pharyngeal gill slits are used for gas exchange and feeding.
This obscure little structure will eventually give rise to the vertebrate jaw, a marvelous example of evolutionary constraint - evolution is constrained to run in certain channels. All subsequent evolution has to start with what's already there. They share a common ancestor with echinoderms, a fact we deduce from their similar larval forms dipleurula larvae and other developmental similarities.
This larval form, incidentally looks strikingly similar to the trochophore larvae of annelids and molluscs. Tunicates are sessile, marine organisms. They are covered with a cellulose cloak, or tunic, which gives this group its name. They exchange gases and filter feed by means of their pharyngeal gill slits. They rely on two prominent siphons, an incurrent and excurrent siphon, to pull water through their bodies. The pharynx is lined with cilia, which draw water in. The suspended organic particles stick to a layer of mucus in the pharynx, and are later eaten.
These siphons are convergent with mollusc siphons. Tunicates look a bit like molluscs, and a bit like a transparent sponge, and may even function like these organisms, but these similarities are entirely superficial, and the three groups are not directly related.
Although these curious animals don't especially look like us, they are very derived from their presumably bilateral and motile ancestors. The larvae of tunicates looks very much like a little tadpole. One of the strongest theories of vertebrate origins suggests that vertebrates arose from tunicate larvae by a process called neoteny.
In neoteny, the juvenile form becomes capable of sexual reproduction, and the adult stage is completely bypassed.
Lancelets are very common in shallow water. They are usually hard to see because they bury themselves in the sand, with only the head end sticking out, so they can filter feed by means of the gill slits in their pharynx.
As you might expect of a sedentary filter feeder, their cephalization is greatly reduced. Note the segmented musculature in the body. Segmentation evolved independently in the vertebrate line, perhaps as an adaptation for burrowing. Vertebrates all have a vertebral column or backbone. The linear series of vertebrae , or backbones, reflects the underlying segmentation of the mesodermal tissues.
Vertebrate embryos show this segmentation clearly in the muscles that line the back of the embryo. Cephalization is very pronounced, vertebrates are generally active animals. Vertebrates have extremely well developed sensory organs, and a complex central nervous system with a brain encased in a protective skull.
Vertebrates have a closed circulatory system, and the sexes are separate. There are seven living classes of vertebrates. Observe the skeletons and live chordates on display. Pay particular attention to the way in which the critters move, and how that movement is reflected in their skeletal structure. Contrast and compare fish, amphibians, reptiles, and mammals with respect to their method of movement, and the structure of the jaw and mouth.
How do these differences relate to their habitat and ecological role niche? Turn your frog over so that the ventral surface is up. Carefully cut through the abdominal wall from between the rear legs to the lower jaw.
Cut through the bones of the pectoral girdle as you reach the area of the front legs try your scissors - they are extremely sharp! Peel back the skin over the abdomen. Note the thin peritoneal membrane that encloses the large coelom which holds the internal organs. If you have a female frog, much of the coelomic space may be filled with eggs. Carefully remove most of the eggs to reveal the internal organs.
Note the large heart , flanked on each side by a prominent lobe of the liver. Lift up the heart to expose the lungs that lie beneath. Lift up the heart, liver, and lungs to expose the esophagus and the top of the stomach.
Note how the esophagus leads up into the pharynx and the mouth. Follow the stomach down to find the small intestine and the large intestine , which leads to the cloaca and the anus. Notice how the intestines are highly coiled to increase surface area for digestion.
Cut through one lung to observe its internal structure. This is partly due to their symmetry and their spiny endoskeleton. First, they all possess five-part radial symmetry around a central disk.
Second, they all possess a very unique water vascular system vascular system based on water. These unique characteristics distinguish echinoderms from other animals in the animal kingdom. What characteristics do echinodermata have found in no other phylum?
No other group with such complex organ systems has radial symmetry. All echinoderms have one thing in common: radial symmetry. This means that the creatures have appendages or body construction which point outward from the center of the body like the spokes on a bicycle wheel. Furthermore, these appendages usually occur in multiples of five, although there are a few exceptions.
The phylum echinoderms is divided into five extant classes: Asteroidea sea stars , Ophiuroidea brittle stars , Echinoidea sea urchins and sand dollars , Crinoidea sea lilies or feather stars , and Holothuroidea sea cucumbers.
The most well-known echinoderms are members of class Asteroidea, or sea stars. Echinoderms are generally found in shallow water near shores or in reef environments but can also live in great depths of water.
Instead of a brain, echinoderms have a ring of nerves located around their mouth area that governs their nervous responses. This ring coordinates their motion, their eating, basically anything that requires nerve control. Firebrick starfish. Echinoderms are separated into 21 classes, based mainly on differences in skeletal structures. The number of extant species exceeds 6,, and approximately 13, fossil species have been described. Echinoderms are an important part of the ocean food chain, keeping seaweed in check as grazers and serving as food sources for animals like otters.
Echinoderms are used as food, medicine, and a source of lime for farmers. Echinoderms have a simple radial nervous system that consists of a modified nerve net consisting of interconnecting neurons with no central brain, although some do possess ganglia. They feed on all sorts of other invertebrates, particularly bivalves, snails, crustaceans, marine worms, other echinoderms and even fish.
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