Detailed Notes on Deuterostomes and Major Vertebrate Groups

Echinoderms

• Phylum Echinodermata

  • Exclusively marine organisms.

  • Deuterostomes with an endoskeleton made of calcareous ossicles.

  • Characterized by pentaradial symmetry as adults (bilateral symmetry during larval stage).

  • Common examples: sea stars, brittle stars, sea urchins, sand dollars, and sea cucumbers.

Symmetry and Endoskeleton

• Symmetry: Adult echinoderms exhibit pentaradial symmetry; however, they are bilaterally symmetrical in their larval stage.

  • Oral Surface: Defines where the mouth is located, opposite the aboral surface.

• Endoskeleton: Composed of calcium carbonate ossicles; epidermis covers it.

  • Can be loosely or tightly joined.

  • All echinoderms have mutable collagenous tissue, allowing for changes in body shape and rigidity.

Starfish Anatomy

• Water-vascular System: Radially organized system crucial for locomotion and feeding.

  • Water enters through the madreporite, flows through the stone canal to the ring canal, and extends into radial canals.

  • Tube Feet: Used for locomotion, feeding, gas exchange; may or may not have suckers.

  • Ampulla: Muscular sac that aids in movement.

Regeneration and Reproduction

• Capable of regenerating lost parts; some reproduce asexually by splitting, but most reproduce sexually.

  • Gonochoric: Separate sexes; gametes released into water leading to free-swimming larvae, with each echinoderm class having a characteristic larval type.

Echinoderm Classes

• Five Taxonomic Classes:

  1. Asteroidea (starfish)

  2. Holothuroidea (sea cucumbers)

  3. Echinoidea (sea urchins, sand dollars)

  4. Crinoidea (sea lilies)

  5. Ophiuroidea (brittle stars)

Chordates

• Phylum Chordata: Distinct internal endoskeleton different from echinoderms (internal, not external).

  • Includes fishes, amphibians, reptiles, birds, mammals.

Chordate Shared Derived Traits

1. Nerve Cord: Runs along the dorsal side; becomes the spinal cord in vertebrates.

2. Notochord: May be replaced by vertebral column during development.

3. Pharyngeal Slits: Present in all vertebrate embryos; develop into facial structures and gills.

4. Postanal Tail: Retained during some stage of development.

Other Chordate Characteristics

• Chordate muscles are arranged in segments called somites.

• Most chordates withdraw from a common internal skeleton facilitating muscle work.

Chordate Subphyla

• Three Subphyla:

  1. Urochordata: Non-vertebrate; tunicates and salps.

  2. Cephalochordata: Non-vertebrate; lancelets.

  3. Vertebrata: Vertebrates with a spinal column.

Subphylum Urochordata

• Tunicates: Larvae have notochord; adults are immobile filter feeders.

Subphylum Cephalochordata

• Lancelets retain their notochord throughout life; primarily burrowing organisms.

Subphylum Vertebrata

• Vertebrates: Chordates with a spinal column that encloses the dorsal nerve cord.

  • Characterized by a distinct head with advanced sensory organs.

Key Innovations Among Vertebrates

• Neural crest: Forms structures unique to vertebrates, such as jaws and teeth.

• Internal Organs: Various complex organs including heart and liver, with a closed circulatory system.

• Endoskeleton: Composed of bone or cartilage, allowing substantial body size and movement.

General Vertebrate Body Plan

• Commonly features a head with a brain, vertebral column, dorsal nerve cord, and limbs; including adaptations for unique functions.

History of Vertebrates

• The first vertebrates appeared in the oceans approximately 530 million years ago.

  • They exhibited basic body plans with a mouth at one end and fins at the other, evolving through significant phases:

  • Jawless fishes (Agnatha)

  • Jawed fishes became prominent

  • Amphibians on land

  • Reptiles as dominant terrestrial vertebrates

  • Birds and mammals emerged post-extinction of dinosaurs.

Fishes

• Most diverse vertebrate group with over half of all vertebrate species.

  • Basis for amphibians’ invasion of terrestrial environments.

Key Characteristics of Fishes

• Vertebral Column: Most fishes have a backbone, but hagfish and lampreys are exceptions.

  • Jaws and Paired Appendages: Adaptations for effective feeding and mobility.

  • Internal Gills: Specialized for extracting oxygen from water.

  • Single-loop Blood Circulation: Efficient transport of oxygen.

Major Fish Groups

• Diverse groupings, examples include:

  • Actinopterygii (Ray-finned): Most species-rich class with bony structures.

  • Actinistia (Coelacanths): Ancient lineage appearing unchanged since the Mesozoic.

  • Dipnoi (Lungfishes): Adapted to breathe air and live on land.

  • Chondrichthyes: Cartilaginous fish (sharks, skates).

History of Fishes

• Early jawless fish left a mark on evolutionary history, leading to later advancements through the development of jaws and paired fins in their descendants.

Emergence of Sharks and Bony Fish

• Significant evolutionary changes occurred in the Devonian period, shifting predator dominance from earlier forms to sharks and various bony fishes.

Class Chondrichthyes

• Includes sharks, skates, and rays with specialized adaptations for predation and robust skeletal structures composed of cartilage.

Bony Fishes

• Characterized by a true bony skeleton. Features include:

  • Swim Bladder: Helps maintain buoyancy.

  • Gill Covers: Movable operculum assists in gill ventilation.

Amphibians

• First vertebrates to transition onto land.

  • Key Adapations:

  1. Legs for support on land.

  2. Lungs for breathing air.

  3. Cutaneous respiration to supplement lung function.

  4. Separate pulmonary circuits for efficient blood circulation.

  5. Partially divided heart facilitates effective oxygen delivery.

Ichthyostega

• Considered one of the earliest amphibians, showcasing transitional traits between fish and amphibians.

Tiktaalik

• A significant transitional fossil between a fish and amphibian, possessing features necessary for surviving on land.

Main Amphibian Groups

• Three Groups:

1. Anura: Frogs and toads, prominent skin adaptations for diverse environments.

2. Caudata: Salamanders with distinct elongation and moist habitats.

3. Apoda: Legless caecilians.

Reptiles

• Class Reptilia: Recognizable features include amniotic eggs, dry skin, and thoracic breathing.

• Adaptations for terrestrial living, including:

  • Amniotic egg: protections against desiccation.

• Major Orders of Reptiles encompass turtles, lizards, snakes, and crocodilians, each with specific adaptations and ecological roles.

Birds

• Class Aves: Distinguished by feathers and adaptations for flight, such as lightweight skeletons. Key innovations include:

  • Hollow bones.

  • Physiological mechanisms enhancing flight efficiency.

Mammals

• Class Mammalia: Defined by features like hair and mammary glands. These adaptations have permitted:

  • Endothermy with high metabolic rates.

  • Specialized teeth corresponding with diverse diets.

Evolution of Primates

• Primates display unique adaptations for climbing and survival in trees, including grasping limbs and complex social structures.

• Distinction between prosimians and anthropoids signifies evolutionary pathways leading to modern humans.

Hominoids and Hominids

• Primates evolved with distinguishing traits separating them from non-human relatives.

  • Shared characteristics with hominoids, enhanced cognitive functions, and tool usage among later hominids.

Early Humans

• The evolutionary path leads through significant species including Homo habilis, Homo erectus, and modern Homo sapiens, each demonstrating increasing brain size and social complexity.