Deuterostomes and Chordates Overview

Overview

This lecture covers Deuterostomes, focusing on Echinoderms and Chordates, and details the evolutionary features, major groups, and key adaptations of vertebrates.

Animal Phyla and Classification

• There are nine main animal phyla, classified by embryonic development.
• Protostomes develop the mouth first; Deuterostomes develop the anus first.

Echinoderms

• Echinoderms are marine deuterostomes with adults showing radial symmetry.
• They possess a water vascular system and tube feet.

Chordates

• Chordata is the ninth animal phylum, defined by four shared features.
• Some chordates, like tunicates and lancelets, are invertebrates.
• Tunicates and lancelets resemble ancestral chordates and have distinct anatomy.

Craniates and Vertebrates

• Some chordates have a cranium (skull); some also have vertebrae (spinal column).
• Hagfishes and lampreys are craniates without jaws, with long, slender bodies.

Evolutionary Adaptations in Chordates

• Some chordates evolved jaws, enabling more efficient feeding.
• Fishes are aquatic vertebrates with jaws; some are cartilaginous, others have bony skeletons.
• Bony fishes split into two major lineages.

Tetrapods and Amniotes

• Amphibians were the first tetrapods (four-limbed vertebrates).
• Amphibians live on land and in water, and have three main lineages.
• Amniotes, including reptiles and mammals, possess the amniotic egg, allowing reproduction away from water.

Reptiles and Mammals

• Reptiles were the first vertebrates to thrive fully on land, divided into five major groups.
• Turtles and tortoises have tough shells; birds are warm-blooded, feathered reptiles adapted to flight.
• Mammals are warm-blooded, have hair, and produce milk; they share a common ancestor with reptiles.
• Mammalian groups: monotremes (lay eggs), marsupials (bear live young), eutherians (bear live young).

Key Terms & Definitions

• Deuterostome — Animal group in which the anus forms before the mouth during embryonic development.
• Echinoderm — Marine deuterostome with radial symmetry and a water vascular system.
• Chordate — Animal with a notochord, dorsal nerve cord, pharyngeal slits, and post-anal tail.
• Craniate — Chordate with a skull.
• Tetrapod — Vertebrate with four limbs.
• Amniote — Vertebrate with an amniotic egg.
• Monotreme — Egg-laying mammal.
• Marsupial — Mammal bearing live young, often in a pouch.
• Eutherian — Placental mammal.

Action Items / Next Steps

• Review mastering concepts for sections 21.2 to 21.16.
• Prepare for clicker question #5 and review the solution.
• Study the summary of chordate diversity for exam preparation.