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Pseudocoelomates are animals whose body cavity is pseudocoelom, i.e. the mesoderm is present as scattered pouches in between the ectoderm and endoderm rather than as a continuous layer. Pseudocoelomate animals are also known as Blastocoelomate animals. A Coelom, also known as a body cavity, is a large fluid-filled space or cavity that exists between the outer body wall and the inner gut wall (walls of alimentary canal). The Coelom houses the majority of the visceral organs and is lined on all sides by mesoderm.
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Key Terms: Pseudocoelomate, Ectoderm, Endoderm, Mesoderm, Coelom.
What are Pseudocoelomates?
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A pseudocoelomate is an organism with a body cavity that is not derived from the mesoderm, as is the case with a true coelomate. Because the body cavity is derived from the blastocoel, or cavity within the embryo, a pseudocoelomate is also known as a blastocoelomate. A true coelom is lined with a peritoneum, which serves to keep fluid from entering the body cavity. In a pseudocoelomate, body fluids bathe the organs and receive nutrients and oxygen from the cavity fluid.
Pseudocoelomates
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Pseudocoelomates Circulatory System
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The pseudocoelom is a fluid-filled body cavity in metazoans that, unlike true coeloms, lacks a cellular peritoneal lining. Most pseudocoelomates (for example, the classes Nematoda and Rotifera) are small and lack an independent vascular system. Muscular body and locomotor movements may aid in the circulation of nutrients within the pseudocoelom, which connects the gut to the body wall.
The lacunar system of channels within the body wall of gutless acanthocephalans (spiny-headed worms) could be used to circulate nutrients absorbed through the body wall. Hemoglobin has been discovered in the pseudocoelomic fluid of several nematodes, but its exact role in oxygen transport is unknown.
Also read: Multicellular Organism
Pseudocoelomates Position in Animal Kingdom
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The embryo's original blastocoel survives as a space, or body cavity, between the enteron and the body wall. Because this cavity lacks the peritoneal lining found in true coelomates, it is referred to as a pseudocoel, and the animals that inhabit it are referred to as pseudocoelomates. Pseudocoelomates are classified as bilateral animals in the Protostomia division, but they are polyphyletic (derived independently from more than one acoelomate ancestor).
Pseudocoelomates Position in Animal Kingdom
Biological Contributions of Pseudocoelomates
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When compared to the solid body structure of acoelomates, the pseudocoel is a distinct gradation in body plan. The pseudocoel may be fluid-filled or contain a gelatinous substance containing mesenchyme cells. It shares certain adaptive potentials with true coeloms, though not all members have them:
- Greater freedom of movement
- Space for development and differentiation of digestive, excretory, and reproductive systems
- A simple means of circulation or distribution of materials throughout the body
- A storage place for waste products to be discharged to the outside by excretory ducts
- A hydrostatic organ, since most pseudocoelomates are quite small, the pseudocoel's most important functions are circulation and maintaining a high internal hydrostatic pressure.
- These phyla, as well as all more complex phyla, have a complete mouth-to-anus digestive tract.
Pseudocoelomates Examples
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- Rotifers: Rotifers are tiny multicellular organisms that live by attaching to a substrate and filter feeding on water. Rotifers have a distinctive head region with hundreds of cilia that work together to create water currents that direct food particles to the mouth. Rotifers, like other metazoans, have three distinct tissues, or are triploblastic. A rotifer embryo, like a human embryo, develops into a blastula. The blastocoel develops inside the embryo into a cavity that is not covered by the peritoneum. The internal organs are bathed in fluid, and oxygen is diffused directly through the small animal's outer layers. This is the most common type of pseudocoelomate, and it is advantageous for the small organism because it does not need a separate circulatory system to circulate oxygen.
- Nematodes: Nematodes, like rotifers, are small pseudocoelomates with a modified body cavity. While the pseudocoelomate condition is sometimes thought to be ancestral, many organisms have advanced body parts, such as nematodes. Nematodes reproduce sexually, produce games, and have advanced reproductive and food-finding organs, as shown in the image below. These organisms can be free-living or parasitic in the soil or water. These small organisms have adapted to nearly every environment on the planet due to their advanced reproductive systems.
Things to Remember
- Pseudocoelomates are animals with a pseudocoelom body cavity, which means the mesoderm is present as scattered pouches in between the ectoderm and endoderm rather than as a continuous layer.
- In the Protostomia division, pseudocoelomates are classified as bilateral animals, but they are polyphyletic (derived independently from more than one acoelomate ancestor).
- The pseudocoelom is a distinct gradation in body plan when compared to the solid body structure of acoelomates. The pseudocoel may be fluid-filled or contain mesenchyme cells in a gelatinous substance.
Sample Questions
Ques: What are Pseudocoelomates? Where is it located? (4 marks)
Ans: Pseudocoelomates are animals whose body cavities are pseudocoelom, i.e. the mesoderm is present as scattered pouches in between the ectoderm and endoderm rather than as a continuous layer. Animals classified as Pseudocoelomate are also known as Blastocoelomate.
Pseudocoelom is also referred to as false Coelom. It is a cavity in the body that is not entirely lined by mesoderm. The mesoderm is found in the form of scattered pouches between the ectoderm and endoderm. This type of body cavity is referred to as a pseudocoelom. The blastocoele of the embryo gives rise to the pseudocoelom. Pseudocoelom is only found in invertebrates. Pseudocoelomates are animals that have pseudocoelom, and the group of animals is known as Pseudocoelomates or Blastocoelomates. Pseudocoelomates lack a blood vascular system, skeleton, segmentation, and a body wall, and the majority of these structures are microscopic. Aschelminthes, for example.
Ques: How useful is the study of the nature of the body cavity and coelom in animal classification? (3 marks)
Ans: Organisms can be classified based on whether or not they have a coelom. Coelom refers to the body cavity lined by mesoderm. Coelomates are animals that have coelom, such as annelids, mollusks, arthropods, echinoderms, hemichordates, and chordates. In some animals, mesoderm does not line the body cavity; instead, it appears as scattered pouches in between the ectoderm and endoderm. Such a body cavity is known as a pseudocoelom, and the animals that have them are known as pseudocoelomates, such as aschelminthes. The body cavity of pseudocoelomates is derived from the embryonic blastocoel. Acoelomates are animals that do not have a body cavity, such as platyhelminthes.
Ques: Distinguish between diploblastic and triploblastic animals. (2 marks)
Ans: Diploblastic animals, such as porifers, coelenterates, and ctenophores, have cells organized in two embryonic layers, an external ectoderm and an internal endoderm. Triploblastic animals are those in which the developing embryo has a third germinal layer, mesoderm, in between the ectoderm and endoderm. For example, Platyhelminthes to Chordates.
Ques: Endoparasites live within the host's body. Mention the unique structure that these have that allows them to survive in those conditions. (3 marks)
Ans: Endoparasitic life cycles are more complex due to their extreme specialization. Their morphological and anatomical features are greatly simplified, while their reproductive potential is highlighted.
Parasites evolve special adaptations based on their lifestyle, such as:
- The removal of unnecessary sense organs.
- Degeneration of the digestive system.
- Abundant reproductive capacity.
- The presence of adhesive organs or suckers that allow the parasite to cling to the host.
Ques: Mammals are the best adapted vertebrates. Elaborate. (3 marks)
Ans: Mammals are the best adapted vertebrates because they can live in a wide range of environments, including polar ice caps, deserts, mountains, forests, grasslands, and*dark caves. Some of them have developed the ability to fly or live in water.
They have two pairs of limbs that allow them to walk, run, climb, burrow, swim, or fly. Mammalian skin is unique in that it contains hair. There are external ears or pinnae. The jaw contains various types of teeth. The heart has four chambers.
They have a 'homeotherm'. The lungs are responsible for respiration. The sexes are separated, and fertilization is done internally. With few exceptions, they are viviparous, and development is direct.
Ques: What significance does the presence of an air bladder have in Pisces? (2 marks)
Ans: The swim bladder, also known as the air bladder, is a sac-like outgrowth of the dorsal wall of the esophagus in bony fishes. It has a hydrostatic function. It controls their buoyancy and allows them to swim up and down, preventing them from sinking. In some species, the air bladder aids in respiration. It also functions as a resonating chamber for producing or receiving sound.
Ques: Could an oviparous and viviparous mother produce the same number of eggs or young? Why? (3 marks)
Ans: No, the number of eggs or young produced by an oviparous and viviparous mother cannot be the same. Oviparous mothers lay a large number of eggs, but because the eggs are laid outside the body, they are vulnerable to predators and harsh environmental conditions and are thus destroyed. However, in viviparous mothers, eggs are not laid outside, but the embryos develop inside the mother and are thus protected from the harsh outside environment, resulting in a lower number of eggs produced. As a result, the number of eggs or young produced by an oviparous and viviparous mother cannot be equal.
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