Phyla - Platyhelminthes & Annelida | Biology for Grade 11 PDF Download

Phylum Annelida

Characteristics of Animals

• Animals display diverse shapes and sizes. Unlike sponges, their bodies are unbranched. Internal organs like the liver, heart, kidney, lungs, brain, and stomach are common. Growth in animals ceases well before their death, with growth regions dispersed throughout the body. They are capable of bodily movement and are heterotrophic, lacking chlorophyll for photosynthesis.

Animal Classification

• Animals are categorized based on factors such as the number of germ layers in the embryo, body symmetry, and the origin of the mouth. The Animalia kingdom is broadly classified according to shared fundamental characteristics. The phyla within the animal kingdom include Porifera, Cnidaria, Ctenophora, Platyhelminthes, Aschelminthes, Annelida, Arthropoda, Mollusca, Echinodermata, Hemichordata, and Chordata.

Phylum Annelida Overview

• Annelids are segmented worms exhibiting a high level of organization. They possess a body divided into segments, each housing specific organs and tissues. An illustrative example of annelids is the earthworm, which showcases the segmented body plan and specialized structures like setae for movement.

Annelids, found in freshwater, seawater, or moist soil, exhibit diverse lifestyles including free-living, burrowing, and parasitic forms. Here are the key characteristics of this phylum:

Annelid Body Structure:

• Annelids possess a segmented body divided into ring-like true segments.
• The body is soft, extensible, and triploblastic, demonstrating organ-level body organization.
• They were the first animals to develop a true coelom, which acts as a hydraulic skeleton.
• Longitudinal and circular muscles are both present, providing movement and support.
• They have a straight and complete alimentary canal for efficient digestion.

Circulatory and Respiratory Systems:

• Annelids were the first animals to possess a closed circulatory system.
• Their blood is red due to hemoglobin dissolved in plasma.
• They respire through cutaneous respiration via their moist skin.

Excretory and Reproductive Systems:

• Excretion is facilitated by nephridia.
• Reproduction in annelids can be unisexual (e.g., Nereis) or bisexual (e.g., Earthworm).
• Fertilization may occur internally or externally.
• Development can be direct or indirect, often involving a free-swimming larval stage like trochophore.

Nervous System and Locomotion:

• The nervous system consists of a dorsal "brain" and a ventral nerve cord, with ganglia and lateral nerves in each body segment.
• For locomotion, annelids possess segmentally arranged paired lateral appendages, parapodia, chitinous setae, or chaetae.

Classification of Annelida

On the basis of the number and presence or absence of setae, the phylum Annelida is divided into the following classes:

Polychaeta

• Polychaetes are predominantly found in marine environments and exhibit well-developed parapodia with numerous setae.
• Their life cycle involves indirect development, including metamorphosis with a free-swimming trochophore larva.
• Examples of Polychaeta include Nereis (Clam worm or sandworm or Ragworm), Aphrodite (Sea mouse), Chaetopterus (Paddle worm), Sabella (peacock worm), Arenicola (lugworm), Amphitrite, Terebella, and Serpula (Fanworm).

Oligochaeta

• Oligochaetes are semi-terrestrial or freshwater annelids characterized by a limited number of setae and the presence of a clitellum.
• They do not undergo metamorphosis during their life cycle.
• Examples of Oligochaeta include Pheretima, Lumbricus, and Tubifex.

Hirudinea

• Hirudinea are ectoparasitic annelids that form a clitellum only during the breeding season.
• They possess botryoidal tissue surrounding their alimentary canal.
• Examples of Hirudinea include Hirudinaria, Pontobdella, and Hirudo.

Summary of Annelids

• Annelids are ectoparasitic worms that belong to the phylum Annelida.
• The clitellum, a reproductive structure, is present only during the breeding season.
• They possess botryoidal tissue surrounding the alimentary canal.
• Examples of annelids include Hirudinaria, Pontobdella, and Hirudo.

Archiannelida

• Archiannelids lack external segmentation but have internal segmentation.
• They do not possess parapodia or setae.
• Examples of Archiannelids are Polygordius and Dinophilus.

Echiurida

• Echiurids do not exhibit external or internal segmentation.
• Setae are uncommon among Echiurids.
• These annelids typically have elongated prostomiums.
• Examples of Echiurids include Bonellia and Echiurus.

Examples

• Nereis
• It is commonly called clam worm or sandworm or ragworm.
• Nereis is unisexual, and its reproductive phase is called Heteronereis.
• During development, a trochophore larva is present.
• Each segment bears laterally one pair of fleshy projections, the parapodia, used in swimming.
• They are cylindrical in shape, found not only in sandy areas, and they are adapted to burrowing.

Clam worm, sandworm, ragworm:

• Nereis is commonly referred to as clam worm, sandworm, or ragworm.

Heteronereis:

• This is the reproductive phase of Nereis.

Trochophore:

• During development, Nereis exhibits a trochophore larva.

Parapodia:

Each segment of Nereis bears fleshy projections called parapodia, which are used in swimming.

• Hirudinaria (Bloodsucking leech)
• It is a facultative ectoparasite of cattle.
• It is sanguivorous.
• Its saliva contains an anticoagulant called hirudin.
• The body cavity is filled with a mesodermal botryoidal tissue formed of branching tubular cells.

Ectoparasite:

Hirudinaria, the bloodsucking leech, is a facultative ectoparasite of cattle.

Sanguivorous:

Hirudinaria is a sanguivorous organism.

Hirudin:

The saliva of Hirudinaria contains an anticoagulant known as hirudin.

Botryoidal tissue:

The body cavity of Hirudinaria is filled with a mesodermal botryoidal tissue made of branching tubular cells.

• Pheretima (Earthworm)
• It is found in wet soil containing rich organic matter.
• It is omnivorous, fossorial, nocturnal, hermaphrodite, and protandrous.
• Earthworms possess a great power of regeneration.
• The body of an earthworm is brown or clay-colored due to the pigment porphyrin.
• The digestive system consists of the alimentary canal and digestive glands.
• The blood vascular system of earthworms is a closed type.

Morphology:

Earthworms found in wet soil rich in organic matter. They are omnivorous, fossorial, nocturnal, hermaphrodite, and protandrous. Earthworms have a remarkable power of regeneration. Their bodies are brown or clay-colored due to the pigment porphyrin. The digestive system comprises the alimentary canal and digestive glands. The blood vascular system is of the closed type.

Earthworm

Economic Importance of Earthworms

• Earthworms thrive in wet soil rich in organic matter.
• They exhibit omnivorous, fossorial, nocturnal, hermaphroditic, and protandrous characteristics.
• Earthworms possess remarkable regenerative abilities.
• Morphology: Earthworms appear brown or clay-colored due to the pigment porphyrin.
• The body of an earthworm displays metameric segmentation.
• The digestive system comprises the alimentary canal and digestive glands.
• Earthworms have a closed-type blood vascular system.

Importance in Agriculture

• Enhanced Soil Fertility: Earthworms significantly improve soil fertility through various mechanisms, making them crucial in agricultural practices.
• Utilization as Bait and Food: They serve as both bait for fishing and a food source. In the past, some societies considered earthworms a food staple, and this practice continues in certain cultures like the Macrea people.
• Commercial Value: Many individuals earn a livelihood by capturing earthworms and providing them to research institutions and scientific facilities.

Platyhelminthes

• Phylum Platyhelminthes is a group of invertebrates characterized by bilateral symmetry and a lack of segmentation. These organisms, commonly known as flatworms or tapeworms, have flat bodies and can be both parasitic and free-living. They belong to the Kingdom Animalia.

Phylum Platyhelminthes

Platyhelminthes, an invertebrate phylum, exhibits bilateral symmetry and lack of segmentation. Commonly referred to as flatworms or tapeworms, these creatures, which possess flat bodies, can exist as both parasites and in free-living states within the animal kingdom.

• Examples of Platyhelminthes include Schistosoma mansoni, Taenia saginata, Taenia solium, and Dugesia tigrina. These organisms are the causative agents of various human diseases such as Schistosomiasis and Cysticercosis. Adequately cooking meat and fish is crucial to prevent infections from these parasites.

Examples of Platyhelminthes

The likes of Schistosoma mansoni, Taenia saginata, Taenia solium, and Dugesia tigrina represent instances of Platyhelminthes. These organisms contribute to a range of human illnesses like Schistosomiasis and Cysticercosis. Properly preparing meat and fish is essential to ward off potential infections caused by these organisms.

Characteristics of Phylum Platyhelminthes

• Platyhelminthes exhibit a dual lifestyle, being both parasitic and free-living organisms.
• They display bilateral symmetry, a fundamental trait in their structural organization.
• With three germ layers, they are categorized as triploblastic organisms.
• Characterized as Acoelomates, Platyhelminthes lack internal body cavities.
• These organisms do not possess cilia and are covered by a soft integument.
• Segmentation is absent in Platyhelminthes, resulting in a dorsoventrally flattened body structure.
• While they have a mouth for ingesting food, they lack both an anus and a developed digestive system.
• Respiration occurs through simple diffusion across the body surface.
• Platyhelminthes are hermaphrodites, housing both male and female reproductive organs within a single body.
• They reproduce both sexually, through gamete fusion, and asexually, employing fission and regeneration.
• Internal fertilization is a characteristic mode of reproduction in this phylum.
• The life cycle of Platyhelminthes often encompasses one or more larval stages.
• Food transportation is facilitated by fluids and connective tissues circulating between body walls and internal organs.

Distinguishing Features of Phylum Platyhelminthes

Platyhelminthes, commonly known as flatworms, possess several unique characteristics that set them apart from other organisms. These features include:

• Regenerative Abilities: Certain species of Platyhelminthes, such as blood flukes, exhibit remarkable regenerative capabilities, allowing them to rejuvenate damaged body parts.
• Soft-Bodied Invertebrates: Members of this phylum lack a rigid internal skeleton, making them soft-bodied invertebrates.
• Parasitic Nature: Some species within the phylum, like blood flukes, are parasitic, causing severe diseases in humans and other organisms.
• Wide Size Variation: Platyhelminthes encompass a diverse range of sizes, with some species growing up to 2-3 feet in length.

Classification of Platyhelminthes

Platyhelminthes are classified based on various characteristics and features. This classification system helps in organizing and understanding the diversity within this phylum.

• Acoelomates: Due to the absence of a body cavity, Platyhelminthes are classified as acoelomates.
• Simple Body Structure: With a flattened body shape and bilateral symmetry, these organisms have a relatively uncomplicated body structure.
• Reproductive Strategy: Platyhelminthes employ both sexual and asexual reproductive methods, contributing to their successful survival and propagation.
• Disease-Causing Agents: Certain parasitic species in this phylum pose significant health risks to humans, highlighting the importance of understanding their classification.

Key Characteristics of Platyhelminthes

• They exhibit both parasitic and free-living lifestyles in their natural habitat.
• Displaying bilateral symmetry, they possess a body plan that can be divided into two similar halves.
• Being triploblastic organisms, they consist of three germ layers during their development.
• Identified as Acoelomates, Platyhelminthes lack body cavities within their structure.
• These organisms do not have cilia and instead have a soft outer covering.
• Unlike segmented organisms, Platyhelminthes lack segmentation and are dorsoventrally flattened.
• While they have a mouth for ingestion, they lack both an anus and a complex digestive system.
• Respiration in Platyhelminthes occurs through simple diffusion across their body surface.
• They are considered hermaphrodites as they possess both male and female reproductive organs within a single body.
• Reproduction in Platyhelminthes happens through sexual fusion of gametes as well as asexual methods like fission and regeneration.
• Internal fertilization is a notable feature observed in this phylum.
• Platyhelminthes typically undergo multiple larval stages in their life cycles.
• Food transportation is facilitated by fluids and connective tissues found between their body walls and organs.

Special Characteristics of Platyhelminthes

• Platyhelminthes exhibit unique features that set them apart from other phyla.
• These features include their parasitic tendencies, bilateral symmetry, and triploblastic nature.
• Additionally, their dorsoventrally flattened body shape and lack of body cavities contribute to their distinctiveness.
• Platyhelminthes' ability to reproduce both sexually and asexually further distinguishes them within the animal kingdom.

Every phylum possesses distinct characteristics that help differentiate them from others, showcasing the diverse adaptations and evolutionary paths in the animal kingdom.

Characteristics of Platyhelminthes

• Platyhelminthes exhibit a unique excretory system characterized by flame cells, a feature exclusive to this phylum.
• The nervous system of Platyhelminthes is distinctly ladder-like, a trait not observed in any other phylum.
• Fertilization in Platyhelminthes is internal and self-contained, distinguishing their reproductive process.
• The body cavity of Platyhelminthes contains connective tissues, a defining attribute within this phylum.

Examples of Platyhelminthes

• Taenia solium (Pork Tapeworm): Taenia solium is a parasitic tapeworm causing Taeniasis, a condition transmitted to humans through the consumption of pork contaminated with the parasite.
• Schistosoma: Schistosoma, also known as blood flukes, belong to the Trematoda class and are responsible for causing Schistosomiasis, prevalent in tropical and sub-tropical regions.
• Echinococcus granulosus (Hydatid Tapeworm): This parasitic worm, also known as the dog tapeworm, infects dogs and leads to Echinococcosis.
• Planaria (Dugesia): Planaria are free-living flatworms found in various habitats, possessing remarkable regenerative abilities.

Classes of Platyhelminthes

Platyhelminthes are categorized into three main classes:

Summary of Invertebrate Platyhelminthes

Turbellaria

• The Turbellaria species are typically found in both freshwater and marine environments. They are not parasitic but rather act as detritivores in aquatic ecosystems.
• Key Features:
  • The body of Turbellaria is flat dorsoventrally.
  • They lack suckers and hooks. Examples include Planaria and Otoplana.

Trematoda

• Trematoda consists of parasitic worms known as flukes that often inhabit multiple hosts.
• Key Features:
  • All species in Trematoda are obligate parasites.
  • They possess both oral and ventral suckers. Examples are Diplozoon, Fasciola, and Hepatica.

Cestoda

• Cestoda includes tapeworm species found in the digestive tracts of humans and other vertebrates.
• Key Features:
  • Hooks and suckers are present in Cestoda.
  • Only parasites are part of this class, causing diseases like Taeniasis and Cysticercosis.
  • Examples of Cestoda species are Beef tapeworm and Fish tapeworm.