Lab 9 Deuterostomes
Deuterostomes and Vertebrates
Overview of deuterostome development and vertebrate diversity.
Focus on understanding all bold and underlined termsāessential for identifying organisms in an exam.
Complete all instructions in RED in the lab notebook, but do not limit to just those.
Recommend note-taking on characteristics for later identification in exams.
Expectation to know phylum and class of organisms examined today, including orders for amphibians and reptiles.
Deuterostome Traits
Bilaterally symmetrical at some point during development.
Anus forms first during embryonic development.
Organisms are triploblastic (three tissue layers).
Includes the phyla Echinodermata and Chordata.
Features:
Bilateral symmetry.
Presence of tissues.
Triploblastic organization.
Deuterostomic features.
Segmentality in some cases.
Phylum Echinodermata
Exclusively marine organisms.
Endoskeleton composed of calcium carbonate plates called ossicles, located beneath the skin, causes visible bumps on the surface.
Bilateral symmetry observed in larval stages, which shifts to pentaradial symmetry in adult forms.
Deuterostome Development: Echinoderms
Example of cleavage and early development in echinoderms.
Zygote undergoes mitosis, called cleavage.
Sequential order of cleavages leads to smaller cells.
Resulting structure, the blastula, is a hollow ball of cells.
Gastrulation: The process where the blastula indents to form an archenteron (primitive gut), transforming it into a gastrula.
The indented area becomes the blastopore.
The remaining structure evolves into the digestive tract as the tube forms throughout the organism.
Slide Examination: Starfish Development Stages
Examination of the slide "Starfish Egg Early/Late Cleavage" with required labels at 100x magnification.
Zygote: Single, large, dark purple round cell.
First Cleavage Stage: Two smaller dark purple round cells surrounded by a line.
Second Cleavage Stage: 4 dark purple cells, overlapping noted.
Later Cleavage Stage: More than 4 purple cells, difficult to count.
Blastula Stage: Round ball of tiny purple cells with a darker ring on the edge.
Gastrula Stage: Similar to the blastula but with an outer ring indented, forming a pocket.
Labels for Gastrula:
Archenteron: The primitive gut.
Blastopore: The opening between the archenteron and outside.
Blastocoel: Hollow area between dermal tissues.
Endoderm: Lining of the archenteron.
Ectoderm: Outer layer of cells.
Water Vascular System in Echinoderms
Unique fluid-filled hydraulic system supporting echinoderms' body and locomotion.
Structure is radially organized with a ring canal.
Radial canals extend from the ring canal into each body branch.
Water entry via madreporite; a sieve-like plate that filters water.
Water flow sequence: from madreporite through stone canal to ring canal, and into extremities via radial canals.
Tube Feet: Hydraulic tubes used for locomotion and prey capture, extending from the radial canal; may have suckers.
Water exits through tube feet.
Sea Star Dissection: Identification of Structures
Identification of parts in the starfish:
Starfish (young):
Ossicles.
Ring canal.
Madreporite (small dark dot near ring canal).
Radial canal.
Tube feet (dark dots on the bottom).
Preserved Sea Star:
Ossicles.
Distinct madreporite.
Tube feet (filament-like structures).
Radial canal.
Phylum Chordata
Characterized by a true internal skeleton.
Major features include:
Nerve cord.
Notochord.
Pharyngeal slits.
Postanal tail.
Phylum includes groupings such as fish, amphibians, reptiles, birds, and mammals.
Vertebrates (Subphylum Vertebrata)
Defined as having a vertebral column that encloses and protects the nerve cord.
Distinct head structure with sensory organs present.
Vertebrate Timeline
Key historical milestones:
545 million years ago: Appearance of jawed fishes.
Amphibians: First vertebrates to colonize land.
Reptiles: Replaced amphibians as dominant terrestrial vertebrates.
Birds and Mammals: Emerged following the Cretaceous mass extinction.
Phylogeny of Vertebrates
Phylogenetic tree includes:
Jawless Vertebrates: Lampreys & Hagfish.
Chondrichthyes: Cartilaginous fishes (sharks, skates, rays).
Actinopterygii: Ray-finned fishes.
Actinistia: Coelacanths.
Dipnoi: Lungfishes.
Amphibia: Amphibians.
Mammalia: Mammals with traits like mammary glands, 4-chambered heart, hair, and synapsid skull.
Amniota and Tetrapoda: Includes reptiles and birds.
Testudines: Turtles.
Lepidosauria: Lizards and snakes.
Crocodilia: Crocodiles and alligators.
Aves: Birds with identifiable traits such as feathers and amniotic eggs.
Major Groups of Fish
Chondrichthyes: Cartilaginous fishes.
Actinopterygii: Ray-finned fishes.
Sarcopterygii: Includes Actinistia (coelacanths) and Dipnoi (lungfishes).
Important note: While Sarcopterygii includes tetrapods, definitions are often incomplete if limited to just these two.
Fish Characteristics
Vertebral column (exceptions: hagfish and lamprey).
Jaws and paired appendages (exceptions exist as above).
Internal gills for gas exchange.
Single-loop blood circulation.
Nutritional deficiency in vertebrates stemming from an inability to synthesize aromatic amino acids, inherited by all descendants.
Class Chondrichthyes
Contains sharks, skates, and rays.
Skeleton primarily made of cartilage reinforced with calcium carbonate granules.
Exhibits internal fertilization.
Characterized by placoid scales (modified teeth).
Possesses a fully developed lateral line system that detects pressure changes in water.
Bony Fishes
Two superclasses:
Actinopterygii:
Features include ray-finned structure, no muscle in fins, leptoid or ganoid scales from dentin.
Requires identification based on specimen dissection to determine group.
Sarcopterygii:
Characterized by fleshy, paired fins supported by bones, ancestors to amphibians, with cosmoid scales.
Class Amphibia
Characteristics indicating adaptation to terrestrial environments:
Leg development.
Lungs for respiration.
Cutaneous gas exchange in addition to lungs.
Pulmonary veins allow higher pressure blood circulation to tissues.
Partially divided heart improves separation of pulmonary and systemic blood circuits.
Transition of Amphibians to Land
Critical adaptations include:
Development of legs to support body weight.
Adaptation of lungs for air-breathing.
Redesign of heart and circulatory systems suitable for larger muscle function.
Reproduction in water to prevent egg desiccation.
Systems to prevent body desiccation.
Amphibian Orders
Major classifications include:
Anura: Frogs and toads.
Caudata: Salamanders.
Apoda: Caecilians.
Identification based on described specimens and laboratory work.
Class Reptilia
Traits defining class:
Amniotic eggs: Watertight, providing crucial benefits for terrestrial life.
Keratin scales: Provide body coverage preventing water loss, leading to dry skin.
Thoracic breathing: Enhances lung capacity allowing efficient air exchange.
Parts of the Amniotic Egg
Important structures include:
Chorion: Outermost layer facilitating gas exchange.
Amnion: Encases the embryo within a fluid-filled cavity.
Yolk sac: Provides nutrition.
Allantois: Functions in waste containment during embryonic development.
Examined advantages of amniotic eggs in colonizing terrestrial environments.
Orders of Reptilia
Classification orders include:
Chelonia: Turtles and tortoises.
Rhynchocephalia: Tuataras.
Squamata: Lizards and snakes.
Crocodylia: Crocodiles and alligators.
Aves: Birds, categorically classified under reptiles.
Identify specimens down to phylum and order.
Class Aves
Essential characteristics include:
Examination of feathers for structure and function.
Retention of numerous ancestral reptilian traits such as amniotic eggs and leg scales.
Distinguishing adaptations:
Feathers as modified scales for flight and insulation.
Flight skeleton with thin, hollow bones, many fused for muscle anchorage.
Keeled breastbone for muscle attachment.
Bird Adaptations for Flight
Key adaptations include:
Feathers providing aerodynamic advantages.
Hollow bones reducing weight for better flight efficiency.
Air sacs create unidirectional airflow through lungs, enhancing oxygenation.
4-chambered heart supporting higher metabolic rates.
Bird Respiratory System
The advantage of a respiratory system featuring air sacs and one-way airflow through lungs, improving gas exchange efficiency and oxygen intake.
Class Mammalia
Diverse group totaling about 5000 species, relatively low compared to other vertebrates, with a vast majority being rodents, bats, shrews, or moles.
Key characteristics include:
Presence of hair for insulation, camouflage, or sensory function.
Mammary glands responsible for secreting milk to nourish offspring.
4-chambered heart for efficient blood circulation.
Diaphragm assisting in respiration.
Specialized teeth reflecting dietary habits.
Skulls Examination
Examination reveals eye socket location differences:
Predators exhibit front-facing eyes; prey often have side-facing eyes.
Teeth structure indicators:
Carnivores possess sharp, blade-like teeth.
Herbivores have flat teeth designed for grinding vegetation.
Classifications possible into carnivores, herbivores, or omnivores based on skull analysis.
Dissection: Perch Fish
Identify both external and internal structures.
Drawing and labeling recommended for better retention.
External Anatomy of Fish
Identification of key external features includes:
External nares.
Eye.
Teeth.
Operculum.
Various fins (spiny dorsal, pectoral, pelvic, lateral line, soft dorsal, caudal, anal).
Gills Examination
Cut operculum along dotted lines for gill exposure.
Observation of gills under a dissecting microscope, noting their structure's influence on surface area and gas exchange efficiency.
Internal Anatomy Dissection
Incisions to be made carefully to not damage organs, ensuring internal membranes are kept intact as much as possible.
Internal Structures Identification
Confirm with instructor upon identifying:
Ventral aorta.
Bulbus arteriosus.
Kidney.
Head region.
Pyloric ceca.
Stomach.
Swim bladder.
Urinary bladder.
Gonad.
Liver.
Pancreas.
Ventricle.
Sinus venosus.
Intestine.