Phylum Hemichordata: Part 3 PDF

Hemichordates and invertebrate chordates are marine organisms that bridge invertebrates and vertebrates in evolution. Hemichordates, like acorn worms, have pharyngeal slits and a dorsal nerve cord but lack a notochord. Invertebrate chordates, including tunicates and lancelets, exhibit chordate featu...

Hemichordates and invertebrate chordates are marine organisms that bridge invertebrates and vertebrates in evolution. Hemichordates, like acorn worms, have pharyngeal slits and a dorsal nerve cord but lack a notochord. Invertebrate chordates, including tunicates and lancelets, exhibit chordate features like a notochord and dorsal hollow nerve cord, with tunicates l o s i n g m o s t of t h e s e a s a d u l t s , w h i l e lancelets retain them throughout life. Both groups are primarily filter-feeders, offering insights into early chordate evolution. Characteristic Features of q Hemichordata is bilaterally symmetrical and triploblastic animal. q They are exclusively marine animals. q They can be solitary or in colonies. q Hemichordata have a true body cavity or coelom. q The digestive tract is complete with an anus and can be in the form of a U shaped tube or straight. q A buccal diverticulum is present in the proboscis. q Body is divided into three regions – Proboscis, Collar and Trunk. q Circulatory system in open type. q Respiration occurs through gills. q A primitive nervous system is present. q Reproduction is mostly sexual reproduction. q Fertilization is external. q Development is mostly indirect. But a few species exhibit direct development. Where Triceratops Lived Hemichordata “Hemi” = half; “Chorda”=chord is a phylum of marine deuterostome animals. Hemichordates share common ancestor with chordata and the rest of the deuterostomes Members of the phyla Hemichordata and Chordata are derived from a common diploblastic or triploblastic ancestor. Figure 1: Phylogenetic Relationships among the Hemichordata and Chordata Figure 2: Cladogram showing hypothetical relationships among deuterostome phyla  Figure 3: Cambrian period is a period of time on the prehistoric timeline that runs from about 541 million years – 485 million years ago. q They appear in the Lower or Middle Cambrian period q Hemichordates and chordates are distantly related deuterostomes derived from a common, as yet undiscovered, diploblastic or triploblastic ancestor Figure 4: Phylogenetic relationship between Hemichordates Acorn worms are solitary worm-shaped organisms They generally live in burrows They are deposit feeders, but some species are pharyngeal filter feeders Family Torquaratoridae are free living detritivores. Many are well known for their production and accumulation of various halogenated phenols and pyrroles Characteristics: 1. Cilia and mucus 2. Digestive tract 3. Nervous system 4. Gas exchange 5. Circulatory system 6. Excretion and osmoregulation 7. Reproduction and development  Cilia and mucus assist acorn worms in feeding Detritus and other particles adhere to the mucus-covered proboscis Tracts of cilia transport food and mucus, both posteriorly and ventrally Ciliary tracts converge near the mouth and form a mucoid string that enters the mouth Acorn worms may reject some substances trapped in the mucoid string by pulling the proboscis against the collar Ciliary tracts of the collar and trunk transport rejected material and discard it posteriorly 2. DIGESTIVE TRACT The digestive tract of enteropneusts is a simple tube. Food is digested as diverticula of the gut, called hepatic sacs, release enzymes. The worm extends its posterior end out of the burrow during defecation. 3. NERVOUS SYSTEM The nervous system of enteropneusts is ectodermal in origin and lies at the base of the ciliated epidermis. It consists of dorsal and ventral nerve tracts and a network of epidermal nerve cells, called a nerve plexus. In some species, the dorsal nerve is tubular and usually contains giant nerve fibers that rapidly transmit impulses. There are no major ganglia. Sensory receptors are unspecialized and widely distributed over the body. 4. GAS EXCHANGE Because acorn worms are small, respiratory gases and metabolic waste products (principally ammonia) probably are exchanged by diffusion across the body wall. In addition, respiratory gases are exchanged at the pharyngeal slits. Cilia associated with pharyngeal slits circulate water into the mouth and out of the body through the pharyngeal slits. As water passes through the pharyngeal slits, gases are exchanged by diffusion between water and blood sinuses surrounding the pharynx. 5. CIRCULATORY SYSTEM The circulatory system of acorn worms consists of one dorsal and one ventral contractile vessel Blood moves anteriorly in the dorsal vessel and posteriorly in the ventral vessel Branches from these vessels lead to open sinuses All blood flowing anteriorly passes into a series of blood sinuses, called the glomerulus, at the base of the proboscis Excretory wastes may be filtered through the glomerulus, into the coelom of the proboscis, and released to the outside through one or two pores in the wall of the proboscis The blood of acorn worms is colorless, lacks cellular elements, and distributes nutrients and wastes 6. EXCRETION AND OSMOREGULATION The worm extends its posterior end out of the burrow during At low tide, coils of fecal material, called , lie on the substrate at burrow openings. 7. REPRODUCTION AND DEVELOPMENT Enteropneusts are dioecious. Two rows of gonads lie in the body wall in the anterior region of the trunk, and each gonad opens separately to the outside. Fertilization is external. Spawning by one worm induces others in the area to spawn— behavior that suggests the presence of spawning pheromones. Ciliated larvae, called tornaria, swim in the plankton for several days to a few weeks. The larvae settle to the substrate and gradually transform into the adult form.  It is a small class of hemichordates found mostly in deep, oceanic waters of the Southern Hemisphere. A few live in European coastal waters and in shallow waters near Bermuda. Zoologists have described approximately 20 species of pterobranchs. Pterobranchs are small, ranging in size from 0.1 to 5 mm. Most live in secreted tubes in asexually produced colonies. CHARACTERISTICS Body is divided into 3 regions, as in enteropneusts – Proboscis – Collar – Trunk The proboscis is expanded and shield-like It secretes the tube and aids in movement in the tube The collar possesses two to nine arms with numerous ciliated tentacles The trunk is U-shaped Pterobranchs use water currents that cilia on their arms and tentacles generate to filter feed. Cilia trap and transport food particles toward the mouth Although one genus has a single pair of pharyngeal slits, respiratory and excretory structures are unnecessary. Gases and wastes exchange by diffusion since Pterobranchs are very small in size REPRODUCTION AND DEVELOPMENT Asexual budding is common in pterobranchs and is responsible for colony formation. Pterobranchs also possess one or two gonads in the anterior trunk. Most species are dioecious, and external fertilization results in the development of a planula-like larva that lives for a time in the tube of the female. This non-feeding larva eventually leaves the female’s tube, settles to the substrate, forms a cocoon, and metamorphoses into an adult Hemichordata. The phylum Chordata includes animals with a notochord, dorsal hollow nerve cord, pharyngeal slits, post-anal tail, and an endostyle or thyroid gland at some stage of life. It is divided into three subphyla: Urochordata (tunicates), sessile filter-feeders with chordate traits in larvae; Cephalochordata (lancelets), small fish-like animals retaining chordate features throughout life; and Vertebrata, animals with a backbone, including fish, amphibians, reptiles, birds, and mammals. Chordates are found in diverse habitats and represent a major evolutionary group. Chordates show four features, at different stages in their life. They are: q Notochord– It is a longitudinal rod that is made of cartilage and runs between the nerve cord and the digestive tract. Its main function is to support the nerve cord. In Vertebrate animals, the vertebral column replaces the notochord. q Dorsal Nerve Cord – This is a bundle of nerve fibres which connects the brain to the muscles and other organs. q Post-anal tail – This is an extension of the body beyond the anus. In some chordates, the tail has skeletal muscles, which help in locomotion. q Pharyngeal slits–They are the openings which connect the mouth and the throat. These openings allow the entry of water through the mouth, without entering the digestive system. Phylum Chordata is divided into three subphyla. They are: q Subphylum Urochordata(Tunica) q Subphylum Cephalaochordata (Lancelets) q Subphylum Vertebrata (Craniata)  Phylum Chordata: Marine invertebrates with a sac-like body covered by a tunic made of tunicin (a cellulose-like substance). Exhibit all chordate features (notochord, dorsal hollow ner ve cord, pharyngeal slits, post-anal tail) during the larval stage. Adult forms lose the notochord and nerve cord, retaining only pharyngeal slits and the endostyle. Filter-feeders, using cilia to draw water into the pharynx and expel waste through the atrial siphon. Habitat Most species are sessile, attaching to substrates like rocks or coral. Some, like salps, are pelagic and free-floating. Morphology Larvae: Tadpole-like, with a notochord and tail for swimming. Adults: Barrel-shaped or globular, with two siphons (inhalant and exhalant). The pharynx is large and perforated with slits for filter-feeding. Tunic serves as a protective outer covering. Reproduction Reproduce both sexually and asexually. Sexual reproduction: Hermaphroditic, producing both eggs and sperm. External fertilization is common. Asexual reproduction: Budding occurs in colonial species. Examples Sea squirts (e.g., Ciona, Ascidia): Sessile adults, common in shallow waters. Salps (e.g., Salpa): Free-floating, often forming large pelagic colonies. Pyrosomes (e.g., Pyrosoma): Colonial, bioluminescent pelagic tunicates.  Phylum Chordata: Small, fish-like marine invertebrates that retain all chordate features (notochord, dorsal hollow nerve cord, pharyngeal slits, post-anal tail, and endostyle) throughout life. The notochord extends the length of the body and persists into adulthood, providing structural support. Lack a distinct head, brain, or vertebrae; instead, they have a simple nerve cord. Filter-feeders, relying on cilia to draw water and capture food particles. Typically buried in sandy substrates with only the anterior end exposed. Morphology Body is elongated, laterally compressed, and translucent. No distinct head or paired fins; body covered by a thin epidermis. Pharynx has numerous gill slits for both respiration and filter-feeding. Simple circulatory system with no true heart; blood is circulated by contraction of blood vessels. Reproduction Reproduce sexually, with separate sexes (dioecious). External fertilization: Gametes are released into the water, where fertilization occurs. The resulting larvae are planktonic before settling and transforming into adults. Examples Amphioxus. This interesting bottom-dwelling cephalochordate illustrates the four distinctive chordate Branchiostoma (Amphioxus): Found in shallow seas, a common example of lancelets. characteristics(notochord, dorsal nerve cord, pharyngeal slits, and postanal tail). The vertebrate ancestor is thought to havehad a similar body plan. A, Internal structure. B, Living amphioxus in typical position for filter feeding. Note the oral hood with tentacles surrounding the mouth.  Phylum Chordata: Vertebrates are animals with a vertebral column (backbone) that replaces the notochord during development in most species. Possess a well-developed endoskeleton made of cartilage or bone. Distinct head region with a brain enclosed in a skull (cranium). Complex organ systems, including a closed circulatory system with a ventral heart and specialized respiratory, excretory, and nervous systems. Exhibit bilateral symmetry and a segmented body plan. Habitat Found in a wide range of habitats, from terrestrial to aquatic and aerial. Morphology Highly diverse in size and form, ranging from tiny fish to large mammals. Body is typically divided into head, trunk, and in some cases, a tail. Appendages (e.g., fins, limbs, or wings) are adapted for locomotion in various environments. Outer covering varies: scales in fish and reptiles, feathers in birds, and fur or skin in mammals. Reproduction Reproduce sexually, with most species exhibiting separate sexes (dioecious). Fertilization may be external (e.g., in fish and amphibians) or internal (e.g., in reptiles, birds, and mammals). Development can be oviparous (egg-laying), viviparous (live birth), or ovoviviparous (eggs hatch inside the mother's body). Examples Fish (e.g., sharks, bony fish): Aquatic vertebrates with gills and fins. Amphibians (e.g., frogs, salamanders): Dual life stages in water and on land. Reptiles (e.g., snakes, lizards): Adapted to terrestrial life with scales. Birds (e.g., sparrows, eagles): Warm-blooded, feathered vertebrates capable of flight. Mammals (e.g., humans, whales): Warm-blooded, fur-covered vertebrates with mammary glands. The Fishes: Vertebrate Success in Water Subphylum Vertebrata  Subphylum Vertebrata: § Primitive vertebrates lacking jaws and paired appendages (fins). § Have a cartilaginous skeleton with no true vertebrae, though they possess a notochord throughout life. § Lack scales; their skin is smooth and covered in mucus. § Simple digestive system without a stomach. § Use gill slits for respiration. § Possess a single nostril and a poorly developed sense of vision in most species. Morphology § Elongated, eel-like body shape. § Lack paired fins but have median fins (dorsal and caudal fins). § Circular, jawless mouth with keratinized teeth adapted for sucking or rasping food. § Simplified circulatory system with a two-chambered heart. § Retain primitive characteristics such as a persistent notochord and lack of bone. Reproduction § Reproduce sexually, with separate sexes (dioecious). § Fertilization is external, and most species are oviparous. § Development involves a larval stage (e.g., ammocoetes in lampreys), which may last several years before metamorphosis into adults. § Little parental care; eggs are often left to develop independently. Examples § Lampreys (e.g., Petromyzon): Parasitic or non-parasitic species with a toothed oral disc used for attaching to hosts or feeding on detritus. Found in freshwater and marine environments. § Hagfishes (e.g., Myxine): Scavengers that feed on dead or dying fish, producing large amounts of slime as a defense mechanism. Exclusively marine.  Subphylum Vertebrata: § Vertebrates with jaws derived from the modification of gill arches, enabling diverse feeding strategies. § Possess paired fins or limbs, improving locomotion and balance. § Have a cartilaginous or bony endoskeleton and a well-developed vertebral column. § Complex sensory systems, including paired nostrils, eyes, and inner ears for balance and hearing. § Advanced organ systems, including a closed circulatory system with a multi-chambered heart. § Include the majority of vertebrate species, from fish to mammals. Morphology § Body Structure: Highly variable depending on the group, but typically divided into head, trunk, and tail. § Jaws: Equipped with teeth or beak-like structures for capturing and processing food. § Fins/Limbs: Paired fins in fish; limbs in tetrapods. § Skeleton: Made of cartilage (e.g., sharks) or bone (e.g., bony fishes and tetrapods). § Scales or Skin: Covered by scales (fish and reptiles), feathers (birds), or fur (mammals). Reproduction § Exhibit a wide range of reproductive strategies: § Oviparous: Egg-laying (e.g., birds, most fish). § Ovoviviparous: Eggs hatch inside the mother (e.g., some sharks). § Viviparous: Live birth (e.g., mammals). § Fertilization may be internal or external. § Parental care varies widely, from none to extensive (e.g., mammals). Examples § Cartilaginous Fishes (Chondrichthyes): Sharks, rays, and skates (e.g., Carcharodon carcharias - Great White Shark). § Bony Fishes (Osteichthyes): Salmon, trout, and seahorses (e.g., Hippocampus - Seahorse). § Amphibians: Frogs, salamanders (e.g., Rana - Frog). § Reptiles: Snakes, lizards, turtles (e.g., Chelonia mydas - Green Sea Turtle). § Birds: Eagles, penguins (e.g., Aquila chrysaetos - Golden Eagle). § Mammals: Lions, humans (e.g., Homo sapiens - Humans). Amphibians: The First Terrestrial Vertebrates Subphylum Vertebrata Dual Life Cycle: § Most amphibians have a biphasic life cycle, with aquatic larval stages and terrestrial or semi-terrestrial adult stages (e.g., tadpoles of frogs). § Moist Skin: Their skin is thin, moist, and permeable, aiding in cutaneous respiration and osmoregulation. It often secretes mucus and may contain glands producing toxins. Respiration: § Amphibians respire through gills (larvae), lungs (adults), and skin (cutaneous respiration) at different life stages or simultaneously. § Ectothermic (Cold-Blooded): § Body temperature depends on the external environment, so they are often restricted to warm, moist habitats. Heart and Circulation: § They have a three-chambered heart (two atria and one ventricle) and a double circulation system, allowing partial separation of oxygenated and deoxygenated blood. Reproduction and Development: § Fertilization can be external (e.g., frogs) or internal (e.g., salamanders). § Eggs are laid in water or moist environments and lack shells. § Larvae undergo metamorphosis to develop into adults, transitioning from aquatic to terrestrial forms. Locomotion: § They exhibit varied modes of locomotion: jumping (frogs), crawling (salamanders), or burrowing. Sense Organs: § Well-developed eyes with eyelids for protection and vision on land. § Tympanum (external ear) detects sound vibrations. § Lateral line system is present in larvae for detecting water currents. Diet:Adults are mostly carnivorous, feeding on insects, worms, and small vertebrates, while larvae are often herbivorous or filter-feeders.  Amphibians: § Amphibians with elongated bodies and tails, retained throughout life. § Exhibit limb regeneration capabilities, especially in newts. § Possess four limbs of roughly equal size, although some species are limbless. § Skin is smooth and moist, aiding in respiration and protection. § Primarily nocturnal, preferring cool, damp habitats. Morphology § Body: Slender, elongated body with a distinct head, trunk, and tail. § Skin: Permeable, with mucus-secreting glands; some have poison glands. § Limbs: Short, equal-sized limbs, aiding in crawling or swimming; some aquatic species may have reduced or absent limbs. § Respiration: Larvae have external gills; adults may use lungs, gills, or cutaneous respiration. § Eyes: Well-developed in most species but reduced in cave-dwelling forms. Reproduction § Reproduce sexually, with internal fertilization in most species. § Males produce spermatophores (packets of sperm) that females pick up with their cloaca. § Eggs are laid in water or moist environments, sometimes attached to vegetation. § Larvae resemble adults but have external gills and develop gradually without a drastic metamorphosis. § Parental care is present in some species, with adults guarding eggs. Habitat § Found in aquatic, semi-aquatic, and terrestrial habitats, typically in temperate regions. § Require moist environments or access to water due to their permeable skin. Examples § Tiger Salamander (Ambystoma tigrinum): A large terrestrial species found in North America. § Axolotl (Ambystoma mexicanum): An aquatic species that retains larval characteristics throughout life (neoteny). § Red-Spotted Newt (Notophthalmus viridescens): Semi-aquatic, with distinct larval, juvenile (eft), and adult stages. § Hellbender (Cryptobranchus alleganiensis): A large, fully aquatic salamander found in streams of North America.  Amphibians: Legless, burrowing or aquatic amphibians resembling worms or snakes. Exhibit poorly developed eyes or are blind; rely on a pair of sensory tentacles near the snout for detecting prey. Skin contains ring-like folds (annuli), giving them a segmented appearance. Found primarily in tropical regions with moist soil or freshwater habitats. Morphology Body: Elongated, cylindrical, and limbless, adapted for burrowing or swimming. Skin: Smooth, with scales embedded in some species; mucus secretion aids in movement and moisture retention. Head: Flattened or pointed, with a small mouth and sensory tentacles for navigation and prey detection. Skeleton: Cartilaginous or bony skull; reduced or absent tail. Respiration: Adults use lungs, but cutaneous respiration is also significant. Reproduction Reproduce sexually, with internal fertilization via a copulatory organ called the phallodeum in males. Many are viviparous, giving birth to live young that are nourished in the oviduct by secretions (uterine milk). Some are oviparous, laying eggs in moist environments. Parental care is common, with females guarding eggs or providing nutrition to hatchlings by allowing them to scrape off skin layers. Lar vae of aquatic species may have gills, while terrestrial species undergo direct development, hatching as miniature adults. Habitat Found in tropical regions of South America, Africa, and Southeast Asia. Live in moist soil, leaf litter, or shallow freshwater environments. Examples Ichthyophis: Found in Southeast Asia; oviparous, with direct development or aquatic larvae. Typhlonectes: Aquatic caecilians found in South America, including viviparous species. Siphonops: Burrowing caecilians from South America, exhibiting maternal care. Caecilia: A genus of large terrestrial caecilians found in tropical forests.  Amphibians: Amphibians without tails in their adult stage. Specialized for jumping and leaping due to strong, elongated hind limbs. Exhibit a biphasic life cycle, with aquatic larvae (tadpoles) and terrestrial or semi-aquatic adults. Smooth or warty skin; some species secrete toxins for defense. Well-developed vocal cords, especially in males, used for communication and attracting mates. Morphology Body: Compact and short, with a broad head and large mouth. Limbs: Hind limbs are long and muscular for jumping; forelimbs are shorter and adapted for support and swimming. Skin: Moist and permeable, facilitating cutaneous respiration; may have poison glands in some species. Eyes: Prominent, with a nictitating membrane for protection. Respiration: Larvae have gills; adults respire through lungs, skin, and the lining of the mouth (buccal respiration). Tail: Present in larvae but absent in adults. Reproduction Reproduce sexually, with external fertilization in most species. Lay eggs in water, often in clumps or strings, coated with jelly for protection. Larvae (tadpoles) are aquatic, herbivorous, or omnivorous, developing into carnivorous adults through metamorphosis. Some species exhibit parental care, such as guarding eggs or transporting tadpoles. Habitat Found worldwide in diverse habitats, from tropical rainforests to deserts. Examples Common Frog (Rana temporaria): Found in Europe, lives in freshwater habitats. American Bullfrog (Lithobates catesbeianus): Large aquatic frog native to North America. Common Toad (Bufo bufo): Found in Europe and Asia, characterized by warty skin. Poison Dart Frog (Dendrobates spp.): Brightly colored, toxic species from Central and South America. Amphibians in Peril Amphibians, a critical group of ver tebrates, are facing a global conser vation crisis. They ser ve as essential bioindicators of ecosystem health due to their permeable skin and dual life stages, yet nearly 41% of amphibian species are at risk of extinction, according to the IUCN. Major Threats to Amphibians § Habitat Destruction: Urbanization, agriculture, deforestation, and wetland drainage lead to the loss of critical breeding and living habitats. Climate Change: Rising temperatures, altered precipitation patterns, and extreme weather events disrupt amphibian breeding cycles and habitats. Pollution: Chemical pollutants, pesticides, and heavy metals contaminate aquatic environments, affecting amphibian development and reproduction. Invasive Species: Predatory fish, cane toads, and other non-native species compete with or prey on amphibians, reducing their populations. Overexploitation: Frogs are harvested for food, pet trade, and scientific research, leading to population pressures in some regions. Ecosystem Imbalance: Amphibians are both predators and prey, playing vital roles in food webs. Their decline can lead to overpopulation of insect pests or affect the diets of predators. § Loss of Biodiversity: Amphibians contribute significantly to global biodiversity, and their extinction would represent a profound loss. Conservation Efforts § Habitat Protection: Establishing protected areas and restoring degraded habitats. § Captive Breeding Programs: Breeding and reintroducing endangered species into the wild. § Public Awareness: Educating communities about the importance of amphibians and reducing harmful practices. § Policy Advocacy: Implementing laws and international agreements to safeguard amphibians and their habitats. Reptiles: The First Amniotes Subphylum Vertebrata §Ectothermic (Cold-blooded): Reptiles rely on external heat sources to regulate their body temperature. They often bask in the sun to warm up and seek shade or burrow to cool down. §Scaly Skin: Reptiles have dry, scaly skin made of keratin. This helps prevent water loss and provides protection. Their skin is shed periodically as they grow, a process known as ecdysis. §Amniotic Eggs: Reptiles lay eggs with a leathery or calcareous shell that provides protection and prevents desiccation. The eggs contain an amniotic sac that allows for the development of the embryo in a controlled environment. §InternalFertilization: Most reptiles reproduce through internal fertilization. In many species, males use specialized structures to transfer sperm into the female's body. §Lungs for Breathing: Unlike amphibians, reptiles rely solely on lungs for respiration. They have well-developed lungs for efficient gas exchange, and most species are obligate air-breathers. §Heart Structure: Reptiles generally have a three-chambered heart (except crocodilians, which have a four-chambered heart), which helps to separate oxygenated and deoxygenated blood. §Excretion:Reptiles excrete nitrogenous waste as uric acid, which conserves water. This adaptation is particularly important in arid environments. §Cold-Blooded Metabolism: Reptiles have slower metabolisms compared to mammals and birds, as they do not generate their own heat and must depend on the external environment for thermal regulation. §Diverse Range of Habitats: Reptiles can be found in a variety of habitats, from deserts and forests to aquatic environments. Some species are fully terrestrial, while others are semi-aquatic or fully aquatic. §Adaptations for Locomotion: Reptiles have different forms of locomotion, including walking, slithering (in snakes), and swimming (in aquatic reptiles). Their limbs (or absence thereof, as in snakes) are adapted to their mode of life.  Reptiles: § Shell: Turtles have a protective shell made of bone, with two parts: the top (carapace) and bottom (plastron). § Cold-blooded: They rely on the environment to regulate their body temperature. § Beak: Turtles don’t have teeth, but they have sharp beaks for eating. § Limbs: § Aquatic turtles have webbed feet or flippers for swimming. § Tortoises have thick, sturdy legs for walking on land. Morphology: § Shape: Aquatic turtles have streamlined bodies, while tortoises have a round, heavy body. § Neck: Long and flexible for most species; some can pull their heads into their shells for protection. Reproduction: § Egg-layers: Female turtles lay eggs on land (even sea turtles). They don't care for their young once the eggs are laid. § Temperature: The temperature of the environment can determine the sex of the baby turtles. Habitat: § Aquatic Turtles: Live in lakes, rivers, and oceans. § Tortoises: Live on land, often in deserts or grassy areas. § Semi-Aquatic: Some turtles live both in water and on land. Examples: § Sea Turtles (e.g., Green Sea Turtle, Leatherback Sea Turtle) – Live in the ocean. § Freshwater Turtles (e.g., Painted Turtle, Red-eared Slider) – Live in ponds and rivers. § Tortoises (e.g., Galápagos Tortoise, African Spurred Tortoise) – Live on land, often in dry areas. § Box Turtles – Live in both water and land environments, with a hinged shell for protection.  Reptiles: Unique Jaw Structure: The tuatara has a specialized "beak-like" jaw, with two rows of teeth on the upper jaw that fit between the teeth of the lower jaw. This makes them different from lizards and other reptiles. Third Eye (Pineal Eye): The tuatara has a "third eye" on top of its head, which is light-sensitive and thought to help with regulating circadian rhythms and seasonal behaviors. Nocturnal: Tuataras are primarily nocturnal, being most active at night due to the cooler temperatures. Morphology: Body Shape: Tuataras are lizard-like in appearance, with a spiny crest along their back and a robust body. Size: Adult tuataras typically grow to around 60 cm (24 inches) in length, making them relatively large reptiles compared to most other species of lizards. Limbs: Tuataras have well-developed, sturdy legs with claws, similar to lizards, although they are not as agile. Reproduction: Slow Reproduction: Tuataras are slow to mature and have a low reproductive rate. They reach sexual maturity at around 10–20 years of age. Egg-Layers: Tuataras lay eggs, typically between 5 and 15 eggs per clutch. The eggs incubate for a long time, up to 12–15 months, which is one of the longest incubation periods among reptiles. No Parental Care: Like most reptiles, tuataras do not provide care for their young after they hatch. Habitat: Endemic to New Zealand: Tuataras are only found in the wild on a few small islands off the coast of New Zealand. They thrive in temperate environments, particularly in coastal areas with rocky terrain and sparse vegetation. Burrows: They live in burrows, often made by seabirds, where they stay to avoid the heat of the day and predators. Cool Environment: Tuataras are adapted to cool environments, as they can tolerate lower temperatures than most reptiles. They are especially active at night. Examples: Tuatara (Sphenodon punctatus): The only living species in the order Rhyncocephali. It is a critically endangered species, primarily found on predator-free islands in New Zealand, where conservation efforts are focused on protecting it.  Reptiles: Scaly Skin: All squamates have dry, scaly skin that they shed. Limbs: Lizards: Most have 4 legs. Snakes: No legs, they slither. Amphisbaenians: Mostly limbless or tiny, hidden legs for burrowing. Tongue: Forked tongue for sensing smells and chemicals. Ectothermic: Cold-blooded, they rely on the environment for warmth. Flexible Jaws (in snakes): Snakes can unhinge their jaws to swallow large prey. Morphology: Lizards: Four legs, long tails, and many can shed their tails for defense. Snakes: Long, limbless bodies that slither. They have flexible jaws for eating large prey. Amphisbaenians: Worm-like bodies, adapted for digging. Reproduction: Sexual: Most reproduce sexually, with internal fertilization. Eggs or Live Birth: Some squamates lay eggs, while others give birth to live young. No Parental Care: Most species don’t care for their young after birth. Habitat: Squamates live in many places like deserts, forests, grasslands, and even water (like sea snakes). Lizards are found in various climates from tropical forests to deserts. Snakes live in forests, grasslands, deserts, and water. Amphisbaenians live underground, mostly in tropical areas. Examples: Lizards:Geckos (small, climbing lizards). Komodo Dragons (large, predatory lizards). Snakes: King Cobra (large venomous snake). Boa Constrictor (large non-venomous snake). Amphisbaenians: Worm Lizard (burrowing, limbless reptile).  Reptiles: Semi-Aquatic: They live in both water and on land. Cold-Blooded: They rely on the environment to regulate their body temperature. Powerful Jaws: Strong teeth for catching and holding prey. Armored Skin: Tough skin with bony plates for protection. Eyes and Nostrils on Top of the Head: These let them see and breathe while mostly submerged. Morphology: Body Shape: Long body with a strong tail for swimming, short legs for walking. Teeth and Jaws: Large teeth for gripping prey. Crocodiles have visible fourth teeth; alligators’ teeth are hidden when their mouths are closed. Tail: Strong and long, used for swimming and balance. Eyes and Nostrils: Positioned on top for breathing and seeing while in the water. Reproduction: Egg-Layers: They lay eggs in nests, with hard, leathery shells. Temperature Determines Sex: The temperature at which the eggs are incubated affects whether they hatch as males or females. Parental Care: Females guard their nests and help the babies to water after they hatch. Habitat: Found in freshwater and saltwater environments like rivers, lakes, and marshes in tropical and subtropical regions. Examples: Crocodiles: Saltwater Crocodile (largest living reptile). Nile Crocodile (found in Africa). Alligators: American Alligator (found in the southeastern U.S.). Chinese Alligator (found in China). Caimans: Spectacled Caiman (found in Central and South America). Black Caiman (found in the Amazon). Gharials: Gharial (long-snouted crocodilian found in India and Nepal). Diversity of Modern Birds 1. Taxonomy of Birds: Birds are classified into two main groups: §Paleognaths (Flightless birds): These birds have a primitive skeletal structure and include large, flightless species like ostriches, kiwis, and emus. They are mostly found in the Southern Hemisphere. §Neognaths (Modern flying birds): This is the larger group and includes nearly all bird species. These birds are capable of flight and have a more developed skeletal structure. Neognaths include groups like passerines (songbirds), raptors (hawks and eagles), waterfowl (ducks and geese), and parrots. 2. Major Groups of Modern Birds: §Passerines (Perching birds): The largest and most diverse group of birds. They include songbirds like sparrows, robins, and finches. They are characterized by three toes pointing forward and one backward, which helps them perch on branches. §Raptors: Birds of prey, such as eagles, hawks, and owls, which have strong talons and beaks for hunting. §Waterfowl: Ducks, geese, and swans, which are adapted to aquatic environments with webbed feet for swimming. §Shorebirds: Waders like sandpipers, herons, and plovers, found along beaches and wetlands, often with long legs and bills for probing the mud. §Parrots: Brightly colored birds like macaws, cockatoos, and parakeets, known for their intelligence and ability to mimic sounds. §Pigeons and Doves: Small to medium-sized birds found worldwide, often with a stocky build and strong flying abilities. §Hummingbirds: Tiny birds known for their ability to hover and rapid wingbeats, feeding on nectar from flowers. Diversity of Modern Birds 3. Key Adaptations: Feathers: All modern birds have feathers, which are key to flight, insulation, and mating displays. Beaks: Birds have specialized beaks adapted to their diet. For example, hawks have sharp beaks for tearing meat, while finches have strong, conical beaks for cracking seeds. Flight: Most birds are adapted for flight with light bones, powerful wings, and strong muscles. However, flightless birds like penguins and ostriches have evolved other adaptations, such as swimming or running. Size: Birds vary greatly in size, from the tiny bee hummingbird (the smallest bird) to the ostrich, the largest living bird. Migration: Many bird species migrate over long distances to find food or reproduce. Examples include swallows and geese. 4. Behavior and Ecology: Feeding Habits: Birds have diverse feeding strategies, including carnivorous birds of prey (e.g., eagles), herbivorous species like parrots and pigeons, and omnivores like crows. Nesting: Birds build nests in various locations depending on species—trees, cliffs, the ground, and even man-made structures. Some species, like emperor penguins, don’t build nests at all but keep their eggs on their feet. Communication: Birds communicate using songs, calls, and body language. Songbirds are particularly known for their complex vocalizations, which are often used to attract mates or defend territories. Courtship: Many birds perform elaborate displays to attract mates, including colorful plumage, dancing, or intricate vocalizations. 5. Conservation and Threats: Many bird species are threatened or endangered due to habitat loss, climate change, hunting, and invasive species. Notable examples include the California condor and the Kakapo. Conservation efforts focus on protecting habitats, breeding programs, and efforts to reduce threats from human activities. The Mammals: The Warm-Blooded Vertebrates Subphylum Vertebrata Diversity of Mammals is vast, encompassing more than 6,400 species that vary greatly in size, shape, behavior, and habitat. Mammals can be found on every continent and in almost every environment, from the deepest oceans to the highest mountains. Here's an overview of the diversity within mammals: 1. Major Groups of Mammals: Mammals are traditionally classified into three main groups based on reproductive methods: 1.1 Monotremes (Egg-laying Mammals): Characteristics: The only mammals that lay eggs. They have a mix of reptilian and mammalian features. Examples:Platypus (Ornithorhynchus anatinus): A semi-aquatic mammal from Australia known for its duck-like bill and webbed feet. Echidnas (Spiny anteaters): Egg-laying mammals with spines on their backs, found in Australia and New Guinea. 1.2 Marsupials (Pouched Mammals): Characteristics: Marsupials give birth to underdeveloped young that continue to develop outside the womb in a pouch. Examples: Kangaroos and Wallabies: Native to Australia, known for their strong hind legs and large tails. Koalas: Arboreal marsupials that live in eucalyptus trees. Tasmanian Devil: A carnivorous marsupial found in Tasmania. Opossums: The only marsupials found in North America. 1.3 Eutherians (Placental Mammals): Characteristics: These mammals give birth to more fully developed young, nourished via a placenta during pregnancy. Examples: Primates: Includes humans, apes, monkeys, and lemurs. Known for their complex brains and social behaviors. Carnivores: Includes lions, tigers, wolves, bears, and weasels. These animals are primarily meat-eaters and often have sharp teeth and claws. Cetacea: Whales, dolphins, and porpoises are fully aquatic mammals adapted to life in the water. Chiroptera: Bats are the only mammals capable of sustained flight. Rodents: The largest order of mammals, including rats, mice, squirrels, and beavers. They typically have sharp, continuously growing incisors. Ungulates (Hoofed Mammals): Includes horses, cows, deer, and pigs, many of which are herbivores with specialized digestive systems for processing plant material. Elephants: The largest land mammals, with trunks and tusks, found in Africa and Asia. Carnivores: Animals like wolves, lions, bears, and otters. Lagomorphs: Rabbits, hares, and pikas known for their long ears and strong hind legs. 2. Mammalian Diversity in Terms of Habitat: Terrestrial Mammals: The majority of mammals live on land. Examples include elephants, lions, and deer, which are adapted to forests, savannas, deserts, and mountains. Aquatic Mammals: Some mammals have adapted to life in the water. This group includes: Whales, dolphins, and porpoises (Cetacea). Seals, sea lions, and walruses (Pinnipedia). Otters, which live in freshwater environments. Flying Mammals: Bats are the only mammals capable of true flight. They occupy a wide range of habitats from forests to urban areas. 3. Mammalian Adaptations: Mammals have adapted to a wide variety of environments and lifestyles: Reproduction and Parental Care: Most mammals provide extensive care for their young, including feeding milk, protecting them, and teaching them survival skills. 4. Notable Mammalian Examples: Humans: As primates, humans have developed complex social systems, language, and technology. Dogs and Cats: Common domesticated mammals that have been bred for various purposes such as companionship, herding, and hunting. Big Cats: Lions, tigers, leopards, and cheetahs are large carnivorous mammals known for their strength, agility, and hunting skills. Rodents: The most diverse group of mammals, including animals like rats, squirrels, and beavers. Marine Mammals: Includes whales, dolphins, and manatees, which are adapted for life in the ocean.  Characteristics of Mammals q Hair or Fur: All mammals have hair or fur at some point in their life, which helps with insulation, camouflage, and sensory functions. q Mammary Glands: Female mammals have mammary glands that produce milk to nourish their young. This is a defining feature of the group. q Warm-Blooded (Endothermic): Mammals are warm-blooded, meaning they can regulate their own body temperature internally, regardless of the environment. q Vertebrates: Mammals have a backbone (vertebral column) made of vertebrae, part of an internal skeleton. q Live Birth (Most Species): Most mammals give birth to live young (viviparous), except for monotremes (platypus and echidna), which lay eggs. q Three Middle Ear Bones: Mammals have three bones in the middle ear (ossicles)—the malleus, incus, and stapes—that are involved in hearing. q Specialized Teeth: Mammals typically have different types of teeth (incisors, canines, molars) for different functions like cutting, tearing, and grinding food. q Breathe Air: Mammals have lungs and breathe air, unlike amphibians or fish, which may rely on gills or other means of oxygen exchange. q Endothermic Circulatory System: Mammals have a four-chambered heart, ensuring efficient circulation of oxygenated blood throughout the body. q Internal Fertilization: Reproduction typically involves internal fertilization, where the male's sperm fertilizes the female's egg inside her body. q Complex Brain and Nervous System: Mammals have highly developed brains and nervous systems, allowing for advanced behaviors, learning, and memory. q Placenta (In Most Species): Most mammals have a placenta during pregnancy, providing nutrients and oxygen to the developing embryo. Mammals, like all living organisms, are subject to various evolutionar y pressures that shape their physical, behavioral, and physiological traits. These pressures arise from interactions with their environment, competition, and the need to adapt to changing conditions. Below are the key evolutionary pressures experienced by mammals:  1. Environmental Pressures qClimate Change: Mammals must adapt to fluctuations in temperature, availability of water, and seasonal variations. For instance, the thick fur and fat layers of polar mammals like polar bears evolved to conserve heat in cold environments. Conversely, desert mammals, like camels, have adaptations for water conservation and heat dissipation. qHabitat Loss and Fragmentation: Urbanization and deforestation force mammals to either migrate, adapt to human-modified environments, or face extinction.  2. Predation and Defense Predator-Prey Dynamics: Predation drives the evolution of defensive adaptations like camouflage, speed, and acute senses. For example, gazelles evolved speed and agility to escape predators like cheetahs. Similarly, armadillos developed hard shells as protection against predators. Social Cooperation for Defense: Many mammals, like meerkats and primates, evolved social behaviors such as group living to better protect themselves from predators.  3. Competition for Resources q Intraspecific Competition (Within the Same Species): Mammals compete for food, mates, and territory. This pressure leads to traits like antlers in deer, used for dominance battles during mating seasons. q Interspecific Competition (Between Different Species): Competition with other species for similar resources can lead to niche differentiation. For instance, some mammals evolved specialized diets to reduce overlap with competitors.  4. Reproductive Pressures Mate Selection (Sexual Selection): Traits like the colorful displays of peacocks or the loud calls of howler monkeys arise from the need to attract mates. Sexual selection can lead to exaggerated features that may not directly benefit survival but enhance reproductive success. Parental Investment: Mammals show a range of reproductive strategies, from producing large numbers of offspring with minimal care to a few offspring with high parental investment. Species like humans and elephants evolved extended parental care to increase offspring survival.  5. Disease and Parasites Immune System Evolution: Exposure to pathogens and parasites drives the evolution of better immune responses. Mammals like bats have unique immune systems that allow them to harbor viruses without getting sick. Co-Evolution with Parasites: Mammals and their parasites are often locked in an evolutionary arms race, with each adapting to counter the other ’s strategies.  6. Human Activity as an Evolutionary Pressure Hunting and Exploitation: Overhunting by humans has led to the extinction of some mammalian species and driven others, like elephants, to evolve smaller tusks or no tusks to reduce poaching risks. Pollution: Environmental toxins can impact mammalian reproduction, behavior, and health, selecting for individuals that are more tolerant of pollutants. Domestication: Humans have artificially selected cer tain mammalian traits, leading to the domestication of species like dogs, cats, and livestock.  7. Cognitive and Behavioral Adaptations Tool Use: Primates and some mammals, like otters, have developed tool-use abilities to improve food access and survival. Problem-Solving and Intelligence: Mammals like dolphins, elephants, and humans have evolved complex brains to navigate social structures and environmental challenges.