How do segmented worms excrete liquid wastes

Water always flows from outside the cell into the cytoplasm; and only then from the cytoplasm into the CV. Species that possess a CV always use it, even in very hypertonic high concentration of solutes environments, since the cell tends to adjust its cytoplasm to become even more hyperosmotic hypertonic than the environment.

The amount of water expelled from the cell and the rate of contraction are related to the osmolarity of the environment. In hyperosmotic environments, less water will be expelled and the contraction cycle will be longer. The number of CVs per cell varies, depending on the species. Amoeba have one; Dictyostelium discoideum , Paramecium aurelia, and Chlamydomonas reinhardtii have two; and giant amoeba, such as Chaos carolinensis , have many.

In some unicellular eukaryotic organisms e. In Paramecium , which, presumably, has the most-complex and highly-evolved CV, the vacuole is surrounded by several canals, which absorb water by osmosis from the cytoplasm. After the canals fill with water, it is pumped into the vacuole. When the vacuole is full, it expels the water through a pore in the cytoplasm that can be opened and closed.

Flame cells and nephridia remove the waste from bodies through filtration in a manner similar to a kidney. As multi-cellular systems evolved to have organ systems that divided the metabolic needs of the body, individual organs evolved to perform the excretory function.

Excretory cells known as flame cells developed in flatworms, while nephridia developed as excretory cells in annelids. Planaria are flatworms that live in fresh water. Their excretory system consists of two tubules connected to a highly-branched duct system that leads to pores located all along the sides of the body. The filtrate is secreted through these pores. The cells in the tubules are called flame cells or protonephridia because they have a cluster of cilia that looks like a flickering flame when viewed under the microscope.

Flame cells function like a kidney, removing waste materials through filtration. The cilia propel waste matter down the tubules and out of the body through excretory pores that open on the body surface; cilia also draw water from the interstitial fluid, allowing for filtration. After excretion, any useful metabolites are reabsorbed by the cell.

Flame cells are found in freshwater invertebrates, such as flatworms, including parasitic tapeworms and free-living planaria. Flame cells and nephridia : In the excretory system of the a planaria, cilia of flame cells propel waste through a tubule formed by a tube cell.

In b annelids, nephridia filter fluid from the body cavity. Earthworms annelids and some other invertebrates, such as arthropods and mollusks, have slightly-more-evolved excretory structures called nephridia. A pair of nephridia is present on each segment of the earthworm. They are similar to flame cells in that they have tubules with cilia and function like a kidney to remove wastes, but they often open to the exterior of the organism.

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. The excretory system of annelid worms consists of a pair of small tubes in each segment.

These tubes, called nephridia from the Greek root word nephrus meaning kidney , are open at both ends. They filter coelomic fluid, which contains useful nutrient molecules along with waste molecules. As the fluid moves through the tube, useful molecules return to the coelom, and waste molecules pass into the water.

This document may be freely reproduced and distributed for non-profit educational purposes. Skip to main content. Search form Search. Join The Community Request new password. Main menu About this Site Table of Contents. Worms: Phyla Platyhelmintes, Nematoda, and Annelida. MS-LS Use argument based on empirical evidence and scientific reasoning to support an explanation for how characteristic animal behaviors and specialized plant structures affect the probability of successful reproduction of animals and plants respectively.

MS-LS Construct a scientific explanation based on evidence for how environmental and genetic factors influence the growth of organisms. MS-LS Gather and synthesize information that sensory receptors respond to stimuli by sending messages to the brain for immediate behavior or storage as memories.

MS-LS Develop and use a model to describe why asexual reproduction results in offspring with identical genetic information and sexual reproduction results in offspring with genetic variation. HS-LS Develop and use a model to illustrate the hierarchical organization of interacting systems that provide specific functions within multicellular organisms. HS-LS Communicate scientific information that common ancestry and biological evolution are supported by multiple lines of empirical evidence.

The content and activities in this topic will work towards building an understanding of the worms in the phyla Platyhelminthes, Nematoda, and Annelida. Introduction to Worms Most people are familiar with earthworms found in garden soil. Roundworms: Phylum Nematoda Species in the phylum Nematoda from the Greek root word nema meaning thread are better known as the roundworms Fig.

Segmented Worms: Phylum Annelida The worms in the phylum Annelida from the Latin root word annelus meaning ring typically have complex segmented bodies Fig. These features appear in some form in all larger, more complex animals: a coelom , a body cavity between the digestive tube and the external body wall that is lined with tissue a circulatory system consisting of a series of tubes vessels filled with fluid blood to transport dissolved nutrients, oxygen, and waste products rapidly and efficiently Recall that the coelom is a fluid-filled cavity lying between the digestive tube and the outer body tube and surrounded by mesodermal tissue.

Further Investigations. Special Features:. Representative Image:. Further Investigations: What is an Invertebrate? Question Set: What is a Mammal? Further Investigations: What is a Mammal? Share and Connect. We invite you to share your thoughts, ask for help or read what other educators have to say by joining our community. Partner Organizations. Professional Development. Purchase a membership! Respiration System. Annelids have two kinds of respiration depending on different classes.

If annelids live in sea or water like annelids in class Polychaeta, they have gills to breathe. Some annelids do not have lugs like earthworm class Oligochaeta , and they use their outer skin to exchange gas. Jinyong El Ouazizi Professional. What is the excretory organ of fish?

The primary excretory organ in fishes , as in other vertebrates, is the kidney. In fishes some excretion also takes place in the digestive tract, skin, and especially the gills where ammonia is given off. Shania El Baz Professional. What are the excretory organs in arthropods? Crustaceans and arachnids possess paired excretory organs maxillary, antennal, or coxal glands that open at the bases of certain appendages.

Myriapods, insects, and some arachnids, such as spiders and mites, possess another type of excretory organ , Malpighian tubules, which open into the intestine. Mohand Denia Explainer. What is the excretory organ of platyhelminthes? Many invertebrates such as flatworms use a nephridium as their excretory organ. At the end of each blind tubule of the nephridium is a ciliated flame cell.

As fluid passes down the tubule, solutes are reabsorbed and returned to the body fluids. Mallie Meyerdierks Explainer.

What is the excretory organ of protozoa? Protozoans : Protozoans have no excretory organs. The metabolic waste products i. They carry out the process of excretion with the help of contractile vacuoles. Germain East Explainer. What is the excretory organ of cockroach? The Malpighian tubule system is a type of excretory and osmoregulatory system found in some insects, myriapods, arachnids, and tardigrades.

The system consists of branching tubules extending from the alimentary canal that absorbs solutes, water, and wastes from the surrounding hemolymph. Yongsheng Minenkov Pundit. What is the excretory organ of Mollusca? Snails, Clams, Oyster etc. Mollucs also have a well developed excretory system , using tubular nephridia organized as kidneys, that collect liquid wastes from the coelom and dump them in the mantle cavity, where they are pumped out of the shell.

Mariela Ashfaq Pundit. What is the excretory unit of earthworm? Fluid from the excretory tubules leaves the body through pores.