Deuterostomes and Chordates Overview

Deuterostomes Overview

• Includes Echinoderms and Chordates

Echinoderms

• Closely related to chordates among invertebrates.
• Characteristics:
• Larval stage is a free-swimming filter feeder, bilaterally symmetrical.
• Adult stage displays radial symmetry; lacks head, brain, or segmentation.
• Anatomy of Sea Star (Figure 19.24):
• Endoskeletal plates, tube feet, central disk, cardiac and pyloric stomachs, coelomic cavity, gonads, anus, and more.

Chordates

• Four essential characteristics present at some life stage:
• Notochord: Dorsal supporting rod, replaced by an endoskeleton in vertebrates.
• Dorsal tubular nerve cord.
• Pharyngeal Pouches.
• Postanal tail.
• Invertebrate Chordates:
• Tunicates (sea squirts) and lancelets maintain all four characteristics.
• Tunicates are sessile as adults, while lancelets retain full chordate features throughout life.

Vertebrates Evolutionary Trends

• Jawless Fishes:
• First vertebrates, cylindrical shape, smooth and scale-less skin.
• Example: Lampreys (parasitic), Hagfishes (scavengers).
• Jaws Evolution:
• Transition from jawless to jawed fish utilizing gill arches (Figure 19.28).
• Cartilaginous Fishes:
• Includes sharks, skates, rays.
• Cartilage skeleton, well-developed senses, lateral line system for pressure detection, keen sense of smell.
• Bony Fishes:
• Most diverse vertebrate group.
• Ray-finned fishes (e.g., perch, salmon) possess a swim bladder for buoyancy.
• Lung Evolution in Fishes:
• Lobe-finned fishes developed lungs, leading to the evolution of amphibians.
• Amphibians:
• Life stages include aquatic larvae and terrestrial adults.
• Adults possess small lungs, supplemented by gas exchange through skin.
• Amniotic Egg:
• Allowed for embryo development on land, providing oxygen, nutrients, and waste management.
• Reptiles:
• Includes turtles, snakes, lizards; protective keratinized scales and three-chambered hearts.
• Birds (Avians):
• Share traits with crocodiles; adaptations for flight include lightweight bones and efficient respiratory systems.
• Mammals:
• Amniotes, generating own heat, characterized by hair and mammary glands for nurturing young.
• Types of Mammals:
• Monotremes: Egg-laying mammals (e.g., platypus).
• Marsupials: Develop immature in a pouch (e.g., kangaroo).
• Placental Mammals: Majority of mammals, adapted for extensive internal development, characterized by 4-chambered hearts and constant internal temperatures.