The cuticle is secreted by and covers a layer of epidermal cells. The body of the Aschelminthes is circular in cross-section, hence, the name roundworms Figure. It can be free-living or parasitic. They may be free-living, aquatic and terrestrial or parasitic in plants and animals.
The free-living organisms are particularly abundant in soils and sediments and they feed on bacteria. Answer: Tube within a tube of body plan is found in the phylum Nematoda. Explanation: Nematodes have a smooth, elongated and cylindrical body structure which is packed in a tough, elastic covering called cuticle. Roundworms have a thick substance called a cuticle on the surface of their bodies that is secreted by the outer epidermal cells….
Anatomy of Roundworms. There are four major groups of parasitic worms: monogeneans, cestodes tapeworms , nematodes roundworms , and trematodes flukes. Helminths are characterized by the presence of attachment organs which include suckers, hooks, lips, teeth, and dentary plates. Sometimes adult worms can be seen moving under the skin. High numbers of blood cells called eosinophils are sometimes found on blood counts. Tissue under the skin is infiltrated by developing larvae of the parasitic worm known as Dracunculus medinensis, or Guinea worm.
A female worm ready to release larvae produces stinging elevated spots papules , causing redness and itching of the skin. The excretory system of Platyhelminthes consists of Protonephridia with Flame cells.
Asexual reproduction of Platyhelminthes occurs either by regeneration or fission. Platyhelminthes are hermaphrodites with internal fertilization. Turbellaria, Trematoda, and Cestoda are the three classes of Platyhelminthes.
Nematoda refers to a phylum of invertebrates with cylindrical bodies. Around 15, species of nematodes have been identified in the world. They are also called roundworms. Since roundworms have a full-fledged body cavity, they are classified as pseudocoelomates.
Nematodes lack a well-defined head. They have a simple digestive system. The mouth is at one end of the body. Nematodes consist of a hard outer covering called cuticle in their epidermis. A nematode is shown in figure 2. Nematodes consist of a life cycle with seven stages: egg, four larval stages, and two adult stages.
Some nematodes are hermaphrodites, and others are dioecious. Platyhelminthes: Platyhelminthes refers to a phylum of invertebrates that comprises flatworms. Nematoda: Nematoda refers to a phylum of invertebrates with cylindrical bodies. The body of an annelid is divided into repeating sections called segments with many internal organs repeated in each segment.
Earthworms class Oligochaeta are familiar terrestrial members of this phylum and leeches class Hirudinea are well-known parasitic members of the phylum, most commonly found in freshwater. They occur mostly in marine and brackish water habitats. Polychaete from the Greek root words poly meaning many and chaeta meaning bristle annelid worms are so named because most of their segments have bristles called chatae or setae.
The free-moving not sessile polychaetes have muscular flaps called parapodia from the Greek para meaning near and podia meaning feet on their sides, and the setae on these parapodia dig into the sand for locomotion. Fireworms are a type of polychaete that have earned their name from stinging bristles on each parapodium Fig.
These bristles can penetrate human skin, causing irritation, pain and swelling, similar to the irritation caused by exposure to fiberglass. Tubeworms are sessile polychaetes that live in tubes that they build by secreting the tube material. The tubes, attached to rocks or embedded in sand or mud, may be leathery, calcareous, or sand-covered depending on the worm species Fig.
Tubeworms feed by extending tentacles from the tube. Bits of food move along grooves in the tentacles to the mouth. Some tubeworms retract their tentacles when food lands on them. Tubeworms use their parapodia to create currents of water that flow through the tubes to aid in respiration and help clean the tubes. By contrast, the free-living or mobile polychaete worms have a proboscis that can extend from their mouths to catch prey.
This is a feeding organ that is often armed with small teeth or jaws on its tip. With their active lifestyle and good defenses, free-moving polychaetes can make their living in a variety of habitats such as mud, sand, sponges, live corals, and algae. Like flatworms, annelids have a mesoderm with muscle, a central nervous system, and an excretory system.
Each of these systems is more complex in the annelid than in flatworms or nematodes. In addition to a more specialized complete digestive system, annelid worms have also evolved body features not found in flatworms or nematodes. These features appear in some form in all larger, more complex animals:.
Recall that the coelom is a fluid-filled cavity lying between the digestive tube and the outer body tube and surrounded by mesodermal tissue. The digestive tube lies inside the outer body tube.
The fluid in the coelom supports the soft tissues of the body wall much as it does in the hydrostatic skeleton of cnidarians. Mesodermal muscles in the wall of the body tube and digestive tube can put pressure on the fluid to aid in movement. In the body wall of the annelids are two types of muscles: circular and longitudinal. When the circular muscles contract, the segment gets longer and narrower. When the longitudinal muscles contract, the segment gets shorter and fatter Fig. These contractions produce the crawling movement of worms.
Recall that nematodes lack circular muscles, and can only move by contracting their longitudinal muscles, thus thrashing and wriggling rather than crawling. The setae along the body of polychaetes stick in the substrate, holding parts of the worm in place while other parts move forward.
Annelids have a closed circulatory system in which blood is pumped along by muscles in blood vessels Fig. Blood flows through the microscopic capillaries, picking up food molecules from the digestive tract and oxygen from the skin and transporting them to the cells of the body.
The parapodia, the flaps on the sides of the segments, increase the surface area of the skin for respiration. Such a system lets animals grow much larger than possible in the flatworms, which must rely on diffusion.
The nervous system is also more complex in annelids than in other worm-like phyla. Annelids have a simple brain organ consisting of a pair of nerve clusters in the head region Fig. Nerves link the brain to sensory organs in the head that detect the environment in front of the worm. Earthworms are eyeless, but polychaete annelids have eyes that can distinguish between light and dark. Some polychaete worm eyes can even detect shapes. Nerves also extend from the brain around the digestive tube and along the ventral surface.
A ganglion or cluster of nerve cells operates the organs in each segment. Turballarian includes all the free-living species e. Trematoda and Cercomeromorpha include all the parasitic flatworms. Trematoda consists of more than 10, known species of flukes Eg: Liver fluke, blood fluke , and Cercomeromorpha includes tapeworms eg: Taenia saginata. Parasitic flatworms can cause diseases to humans. Thus they are important medically and veterinary.
Nematodes or roundworms are pseudocoelomates and have unsegmented bilateral symmetrical bodies. Scientists believed that there are more than 25, species of nematodes are present in the world. Nematodes are abundantly found in terrestrial, marine, and freshwater habitats and many live in animal and plant bodies as parasites.
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