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1. ANIMAL DIVERSITY Unit – 2 Coelomate Protostomes, Arthropoda , Mollusca and Coelomate Deuterostomes BSc. Botany Honours 2 nd semester Utkal University G.E. 2.1 - Zoology Lecture - 9

2. Topic To Be Covered…. General characters of Annelida Metamerism General characters, Social life in insects General characters of Mollusca torsion in gastropod pearl formation General characters of Echinodermata larval form in Echinodermata

3. General characters of Annelida The general characteristics of Annelida, commonly known as segmented worms Segmentation: The body of annelids is divided into segments called metameres . Each segment is separated by a septum and contains repeated organs . Body Structure: They have a cylindrical, elongated body covered with a thin cuticle . Their body wall consists of an outer layer of circular muscle and an inner layer of longitudinal muscle . Coelom : Annelids possess a true coelom (body cavity) that is well-developed and divided by septa. The coelom is filled with coelomic fluid, which acts as a hydrostatic skeleton . Locomotion : Movement is facilitated by the contraction of muscles along with the use of bristle-like structures called setae or chaetae, which provide traction.

4. Digestive System: They have a complete digestive system with a mouth, pharynx, esophagus, crop, gizzard, intestine, and anus. The digestive tract runs straight through the body . Circulatory System: Annelids have a closed circulatory system with blood vessels. Blood is circulated through dorsal and ventral vessels connected by segmental vessels . Nervous System: The nervous system consists of a pair of cerebral ganglia (brain) connected to a ventral nerve cord, with ganglia in each segment . Excretory System: They excrete waste through nephridia , which are paired excretory organs in each segment . Respiration : Gas exchange occurs through the skin, gills, or parapodia , depending on the species . Reproduction : Annelids can be hermaphroditic (both sexes in one individual) or have separate sexes. Reproduction can be sexual or asexual (through fragmentation and regeneration ). Habitat : Annelids can be found in various habitats, including marine environments, freshwater, and moist terrestrial soils . Examples : Common examples of annelids include earthworms ( Oligochaeta ), leeches ( Hirudinea ), and polychaetes ( Polychaeta ).

5. Metamerism Metamerism , also known as segmentation, is a fundamental characteristic of the phylum Annelida. Metamerism Definition: Metamerism is the condition of having a body composed of a series of repeating segments. Each segment is called a metamere or somite . Structure : In annelids, the body is divided into a linear series of segments, which are essentially repeated units along the length of the organism. Each segment is separated from the next by a septum (internal partition ). Components : Each segment typically contains replicated sets of organs and structures, such as : Musculature : Each segment has its own set of muscles, which allows for independent and coordinated movement . Nervous System: There are segmental ganglia and nerve cords in each segment, with the ventral nerve cord running the length of the body . Excretory System: Nephridia , which function in excretion, are present in each segment . Circulatory System: Blood vessels are segmented, with connections between segments to ensure circulation.

6. Advantages of Metamerism : Flexibility and Mobility: Segmentation allows for more efficient and flexible movement, as different parts of the body can move independently . Redundancy : The replication of organs in each segment provides a form of redundancy, which can be beneficial for survival if some segments are damaged . Complexity and Specialization: Over evolutionary time, segments can become specialized for different functions, leading to greater complexity and adaptability . Examples in Annelids : Earthworms ( Oligochaeta ): Segments are externally visible as ring-like structures and internally separated by septa. Each segment contains nephridia , setae, and muscle layers . Leeches ( Hirudinea ): Although leeches have a fixed number of segments, they exhibit metamerism internally with repeated structures . Polychaetes ( Polychaeta ): These marine annelids have well-developed segments with parapodia (paired appendages) on each segment for locomotion.

7. ANIMAL DIVERSITY Unit – 2 Coelomate Protostomes, Arthropoda , Mollusca and Coelomate Deuterostomes BSc. Botany Honours 2 nd semester Utkal University G.E. 2.1 - Zoology Lecture - 10

8. General characters, Social life in insects General Characteristics of Insects Body Structure : Segmentation : The body of insects is divided into three main parts: the head, thorax, and abdomen . Exoskeleton : Insects possess a chitinous exoskeleton that provides protection and support . Appendages : They have jointed appendages, including antennae on the head, legs attached to the thorax, and often wings . Head : Sensory Organs: The head bears sensory organs such as compound eyes, simple eyes ( ocelli ), and antennae . Mouthparts : Various types adapted for different feeding habits, including chewing, piercing-sucking, sponging, and siphoning . Thorax : Segments : Consists of three segments: prothorax , mesothorax , and metathorax , each with a pair of legs . Wings : Typically, the mesothorax and metathorax bear wings, if present . Abdomen : Segments : Generally composed of 11 segments, but the number can vary . Reproductive Organs: Contains reproductive structures, spiracles for respiration, and may have various appendages . Respiratory System: Insects breathe through a network of tracheae and spiracles, allowing for efficient gas exchange . Circulatory System: They have an open circulatory system with hemolymph instead of blood, which is pumped by a dorsal heart . Nervous System: Comprises a central brain, ventral nerve cord, and segmented ganglia .

9. Reproduction: Typically sexual reproduction with separate sexes, though some can reproduce asexually (parthenogenesis). Insects lay eggs . Development: Metamorphosis : Insects undergo metamorphosis, which can be complete (egg, larva, pupa, adult) or incomplete (egg, nymph, adult).

10. Social Life in Insects Social Insects: Insects that live in highly organized colonies or societies. Examples include ants, bees, termites, and wasps . Characteristics of Social Insects : Division of Labor: Different individuals perform specific roles, such as workers, soldiers, and reproductive individuals (queens and drones ). Cooperative Care: Cooperative brood care, where individuals care for the young collectively . Overlapping Generations: Multiple generations live together, allowing for sustained social interactions and care of offspring.

11. Communication : Pheromones: Chemical signals for trail marking, alarm signaling, and colony recognition . Tactile Communication: Physical interactions such as antennal tapping or grooming . Acoustic Signals: Sounds produced by stridulation (rubbing body parts together) or wing vibrations . Eusociality : Definition: The highest level of social organization, characterized by cooperative brood care, reproductive division of labor, and overlapping generations . Examples : Honeybees ( Apis mellifera ) exhibit eusocial behavior, with a clear hierarchy and division of labor within the hive.

12. Advantages of Social Life: Enhanced Survival: Protection against predators and efficient foraging due to cooperative efforts . Resource Allocation: Efficient division of labor and resource management within the colony . Reproductive Success: Increased reproductive success due to specialized roles and cooperative care.

13. ANIMAL DIVERSITY Unit – 2 Coelomate Protostomes, Arthropoda , Mollusca and Coelomate Deuterostomes BSc. Botany Honours 2 nd semester Utkal University G.E. 2.1 - Zoology Lecture - 11

14. General characters of Mollusca

15. Body Structure : Molluscs have a soft, unsegmented body . The body is divided into three main parts: head, visceral mass, and foot . The visceral mass contains most of the internal organs . The head contains sensory organs and the mouth . The foot is used for locomotion and varies in shape among different classes . Shell : Most molluscs have an external shell made of calcium carbonate . The shell is secreted by the mantle, a significant part of the mollusc's anatomy . In some molluscs , such as squids and octopuses, the shell is reduced or internal . Mantle and Mantle Cavity : The mantle is a significant tissue that covers the visceral mass . The mantle cavity houses the gills or lungs and opens to the outside, allowing for gas exchange . Radula : Many molluscs possess a radula, a unique feeding organ . The radula is a ribbon-like structure with tiny teeth used to scrape or cut food before ingestion.

16. Coelom : Molluscs have a reduced coelom, primarily around the heart, gonads, and part of the kidneys . The main body cavity is a hemocoel , which functions as part of the circulatory system . Circulatory System : Molluscs have an open circulatory system, where blood flows through vessels and open spaces called sinuses . The heart typically consists of one or two auricles and one ventricle . Respiration : Aquatic molluscs breathe using gills located in the mantle cavity . Terrestrial molluscs have evolved lungs, also located in the mantle cavity.

17. Excretory System: Molluscs excrete waste through nephridia , which are similar to kidneys . Nervous System : The nervous system includes paired nerve cords and ganglia . The complexity of the nervous system varies among different classes, being more advanced in cephalopods . Reproduction : Molluscs can be dioecious (separate sexes) or monoecious (hermaphroditic ). Fertilization can be external or internal, depending on the species . Development : Molluscs undergo various larval stages, such as trochophore and veliger, which are typical in many marine molluscs . Direct development is also observed in some species.

18. torsion in gastropod

19. Torsion in gastropods is a unique developmental process that distinguishes them from other mollusks. It involves a 180-degree twist of the body during larval development . It involves a 180° counterclockwise rotation of the mantle, mantle cavity, and visceral mass relative to the head and foot of the gastropod . This rotation brings the mantle cavity and anus to an anterior position above the head, and twists the digestive tract into a U shape. The gills, anus, and apertures that form the excretory and reproductive systems are also positioned right below the brain and nerve cords . Torsion changes the gastropod's body from bilateral to asymmetrical , and theories on its evolution suggest it provides advantages for both larvae and adults. For larvae, it may function as a defense mechanism by allowing them to first pull their head into the shell, then seal the aperture with their foot and operculum . For adults, it may provide stability and improve water flow.

20. Definition : Torsion is the 180-degree twisting of the visceral mass, mantle, and shell of gastropods during their larval development . Mechanism : Early Development: Gastropods start as bilaterally symmetrical organisms . Torsion Event: During the larval stage (specifically the veliger stage), a complex set of muscle contractions causes the visceral mass to rotate 180 degrees . Result : The mantle cavity, gills, anus, and nephridia (excretory organs) are repositioned from the posterior to the anterior end, over the head.

21. Stages of Torsion : Initial Twisting: Muscle contractions begin the rotation . Final Position: The body achieves the 180-degree twist, completing torsion . Implications : Anatomical Changes: The repositioning changes the location of the anus and mantle cavity to the front of the body . Advantages: Protection : The head can be withdrawn into the shell for protection . Sensing Environment: Having the mantle cavity and sensory organs at the front helps in better sensing the environment and protection from predators . Disadvantages: Fouling : The anus opens over the head, which can lead to waste fouling the gills and sensory organs. Some gastropods have adapted by evolving mechanisms to avoid fouling, like the development of asymmetrical or coiled shells.

22. Evolutionary Significance : Torsion is considered an evolutionary adaptation that offers protection and enhances sensory capabilities, despite its drawbacks . Example: Snails : Typical examples of gastropods that undergo torsion. Their coiled shells and the positioning of the body parts reflect the results of torsion . Summary: Torsion is a hallmark of gastropod development, resulting in significant anatomical and functional changes. It represents a unique evolutionary adaptation that has both benefits and challenges for these mollusks.

23. ANIMAL DIVERSITY Unit – 2 Coelomate Protostomes, Arthropoda , Mollusca and Coelomate Deuterostomes BSc. Botany Honours 2 nd semester Utkal University G.E. 2.1 - Zoology Lecture - 12

24. pearl formation Pearl formation is a fascinating natural process that occurs within certain mollusks, such as oysters and mussels.

25. Introduction to Pearl Formation Pearls are formed as a defense mechanism against an irritant inside the mollusk. The irritant can be a parasite, a piece of shell, or even a small grain of sand that gets trapped inside the mollusk's shell .

26. The Process of Pearl Formation Irritant Enters the Mollusk : When an irritant enters the mollusk, it becomes lodged in the mantle tissue, which is responsible for shell formation . Secretion of Nacre : To protect itself, the mollusk secretes layers of nacre (also known as mother-of-pearl), a combination of calcium carbonate ( CaCO ₃) in the form of aragonite or calcite, and conchiolin , an organic protein substance . The nacre layers are deposited around the irritant, gradually forming a pearl. Layering Process : The mollusk continues to deposit layers of nacre over months and years, resulting in the development of a pearl . The thickness and number of nacre layers determine the quality and luster of the pearl.

27. 3. Types of Pearls Natural Pearls: Formed without human intervention, these pearls are rare and highly valued . Cultured Pearls: Formed with human assistance by inserting an irritant into the mollusk. Cultured pearls can be produced in freshwater or saltwater environments . Freshwater Pearls : Produced by freshwater mussels, these pearls can come in various shapes, sizes, and colors . Saltwater Pearls : Produced by oysters in saltwater environments, these pearls are often more round and lustrous.

28. 4. Factors Affecting Pearl Quality Luster : The quality of the pearl's surface reflection. High-luster pearls are more valuable . Surface: The presence of blemishes or imperfections on the pearl's surface can affect its value . Shape: While perfectly round pearls are highly prized, other shapes like oval, button, and baroque also have value . Size: Larger pearls are generally more valuable, but size alone does not determine the value; luster and surface quality are also crucial . Color: Pearls come in various colors, including white, black, gray, blue, green, and pink. The color can influence the pearl's value based on rarity and demand.

29. 5. Harvesting and Culturing Pearls Natural Pearl Harvesting : Divers collect oysters from the sea. Since natural pearls are rare, this method yields few pearls . Cultured Pearl Farming : Farmers carefully insert a nucleus (irritant) into the mollusk and then return it to the water to allow nacre deposition . This process can be closely monitored to ensure the production of high-quality pearls.

30. 6. Environmental and Ethical Considerations Sustainability : Responsible pearl farming practices are crucial for maintaining healthy mollusk populations and aquatic ecosystems . Conservation: Efforts to protect natural pearl oyster beds and regulate pearl harvesting help preserve biodiversity.

31. ANIMAL DIVERSITY Unit – 2 Coelomate Protostomes, Arthropoda , Mollusca and Coelomate Deuterostomes BSc. Botany Honours 2 nd semester Utkal University G.E. 2.1 - Zoology Lecture - 13

32. General characters of Echinodermata

33. Echinodermata is a phylum of marine animals known for their unique characteristics. general characters of Echinodermata : Radial Symmetry: Adult echinoderms exhibit pentaradial symmetry, meaning their body parts are arranged in fives or multiples of five around a central axis. However, their larvae are bilaterally symmetrical . Endoskeleton : They possess an internal skeleton made up of calcareous ossicles or plates, which can sometimes be spiny . Water Vascular System: One of the most distinctive features of echinoderms is their water vascular system, a network of hydraulic canals used for locomotion, feeding, and respiration. This system includes tube feet, which extend through pores in the skeleton . Regeneration : Echinoderms have remarkable regenerative abilities, being able to regrow lost body parts, including arms and sometimes even internal organs . Coelom : They have a well-developed coelom (body cavity) which is divided into three parts: the protocoel , mesocoel , and metacoel .

34. Nervous System: Their nervous system is decentralized, lacking a brain. Instead, they have a nerve ring around the mouth and radial nerves extending into the arms . Circulatory System: Echinoderms possess a simple, open circulatory system, often referred to as a hemal system, which is not as well developed as in other animal phyla . Reproduction : Most echinoderms are dioecious , meaning they have separate sexes. Fertilization is usually external, and they often have a planktonic larval stage that undergoes metamorphosis into the adult form . Locomotion : Movement is typically achieved through the coordinated action of tube feet, operated by the water vascular system . Habitat : Echinoderms are exclusively marine and are found at various ocean depths, from the intertidal zone to the deep sea . Examples of echinoderms include starfish ( Asteroidea ), sea urchins ( Echinoidea ), brittle stars ( Ophiuroidea ), sea cucumbers ( Holothuroidea ), and sea lilies or feather stars ( Crinoidea ).

35. larval form in Echinodermata Echinoderms exhibit various larval forms during their development. Each class within the phylum Echinodermata has its own distinct larval stage . Here are the main larval forms : Bipinnaria : This is the first larval stage of sea stars ( Asteroidea ). It is free-swimming and bilaterally symmetrical, with bands of cilia used for locomotion and feeding . Brachiolaria : This follows the bipinnaria stage in sea stars. It develops three adhesive arms used for attachment before metamorphosing into the adult form . Auricularia : This is the larval form of sea cucumbers ( Holothuroidea ). It is planktonic and has a ciliated band around its body for swimming and feeding . Doliolaria : In sea cucumbers, the auricularia larva transforms into the doliolaria stage before becoming a juvenile. It has a barrel-shaped body and is ciliated.

36. Ophiopluteus : This larval form is found in brittle stars ( Ophiuroidea ). It has long, ciliated arms that help with locomotion and feeding . Echinopluteus : This is the larval form of sea urchins ( Echinoidea ). It has elongated arms with cilia, which are used for swimming and capturing food particles . Dipleurula : This is a hypothetical ancestral larva believed to be the common ancestor of all echinoderm larvae. It is a simple, ciliated, bilaterally symmetrical larva . Pentacrinoid : This is the larval stage of crinoids (sea lilies and feather stars). It is sessile and attaches to the substrate with a stalk before developing into the adult form.

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