Chapter 32: The Deuterostomes

Overview of Content

Focus on understanding Deuterostomes through the following detailed objectives, guiding study and comprehension.

Key Learning Objectives

1. Review of Protostome vs. Deuterostome Development

• Protostomes exhibit spiral cleavage, whereas deuterostomes demonstrate radial cleavage.

• In protostomes, the blastopore develops into the mouth, while in deuterostomes, it becomes the anus.

• Development may be traced using earlier cladograms that illustrate these patterns.

2. Ancestral and Derived Features

• Ancestral Features Leading to Echinoderms: Radial symmetry, water-vascular system, and a calcareous endoskeleton.

• Derived Features Leading to Chordates: Presence of a notochord, dorsal nerve cord, pharyngeal slits, and post-anal tail.

• Derived Features Leading to Vertebrates: Development of vertebral column, cranium, and complex nervous tissue.

• Four Major Phyla of Deuterostomes: Echinodermata, Chordata, Hemichordata, and Xenacoelomorpha.

3. Characteristics of Echinoderms

• Echinoderms are exclusively marine organisms with a unique water-vascular system utilized for locomotion and feeding.

• They exhibit pentaradial symmetry as adults, with bilateral symmetry in larval stages.

• Examples include sea stars (Asteroidea), sea urchins (Echinoidea), and sea cucumbers (Holothuroidea).

4. Major Classes of Echinoderms

• Asteroidea (Sea Stars): Have multiple arms radiating from a central disc. They are predators and have the ability to regenerate limbs.

• Crinoidea (Sea Lilies and Feather Stars): Have a cup-shaped body with long feathery arms for filter feeding.

• Echinoidea (Sea Urchins and Sand Dollars): Characterized by a hard shell (test) and movable spines, they are primarily grazers and scavengers.

5. Features of Chordates and Vertebrates

• Shared derived features include a notochord, dorsal hollow nerve cord, and pharyngeal slits.

• Vertebrates additionally possess a vertebral column, a cranium encasing the brain, and specialized sense organs.

6. Characteristics of Invertebrate Subphyla

• Urochordata (Tunicates): Have a sac-like body, with gill slits in adults. The larval stage retains all chordate characteristics.

• Cephalochordata (Lancelets): Share all four key chordate features throughout life; filter feeders that live buried in sand.

7. Vertebrate Cladogram

• The major groupings within vertebrates include:

  • Craniates: Organisms with a skull, including jawless fish.

  • Vertebrates: Craniates with a backbone.

  • Tetrapods: Include amphibians, reptiles, mammals, and birds.

  • Amniotes: Tetrapods with an amniotic egg, including reptiles and mammals.

• Specific classes include Myxini, Petromyzontida, Chondrichthyes, Actinopterygii, Actinistia, Dipnoi, Amphibia, Reptilia, Aves, and Mammalia.

8. Major Features and Clades of Vertebrates

• Jawless Fish (Class Myxini, Petromyzontida): Soft-bodied, lack vertebrae and jaws.

• Cartilaginous Fish (Class Chondrichthyes): Sharks and rays with cartilage skeletons.

• Bony Fish (Class Actinopterygii): Have a swim bladder and varying reproduction strategies.

• Amphibians (Class Amphibia): Undergo metamorphosis and have diverse respiratory structures.

• Reptiles (Class Reptilia): Adapted to land with certain modifications for reproduction.

• Birds (Class Aves): Endothermic, feathers, and distinct endothermic characteristics.

• Mammals (Class Mammalia): Include monotremes, marsupials, and placental mammals with derived traits like hair and mammary glands.

9. Reproductive Strategies

• Oviparous: Species that lay eggs (e.g., birds).

• Viviparous: Animals that give live birth (e.g., most mammals).

• Ovoviviparous: Animals that have eggs that hatch inside the body (e.g., some snakes).

10. Ray-Finned vs. Lobe-Finned Fish

• Ray-Finned Fish: Have thin, flexible fins supported by rays; generally bony.

• Lobe-Finned Fish: Possess fleshy, lobed fins; demonstrated a closer evolutionary relationship to tetrapods.

11. Evolution of Tetrapods from Lobe-Finned Fish

• Evidence shows that lobe-finned fish adapted their lobed fins for walking on land, giving rise to early terrestrial vertebrates.

• This transition involved both skeletal and physiological adaptations for life on land.

12. Clades of Modern Birds

• Major clades include Neornithes (modern birds) and their derived features include adaptations for flight and endothermy.

• Comparison focuses on features like body size, beak shape, and feather types relative to ecological niches.

13. Comparison of Mammal Types

• Protherians (Monotremes): Egg-laying mammals (e.g., platypus), with characteristics similar to reptiles.

• Metatherians (Marsupials): Carry and nurse young in pouches (e.g., kangaroos) with short gestation periods.

• Eutherians (Placental Mammals): Longer gestation periods with more developed young at birth, possessing complex organ systems.