Deuterostomes Overview

Chapter 34: Deuterostomes

Overview of Deuterostomes

Deuterostomes include two main phyla: Echinodermata and Chordata. This group is characterized by developmental attributes where the first opening during embryonic development becomes the anus, in contrast to protostomes where the mouth develops first.

Phylum Echinodermata

Echinoderms are exclusively marine organisms featuring:

  • Endoskeleton: Composed of calcium carbonate ossicles covered by epidermis.
  • Pentaradial Symmetry: Adults exhibit five-part symmetry, while larvae are bilaterally symmetrical. This transition in symmetry indicates that echinoderms evolved from bilaterally symmetrical ancestors.
Key Characteristics and Structure
  • Water Vascular System: This unique system is radially organized and comprises a ring canal leading into radial canals that extend into body branches. It features:
    • Tube feet, used for movement and feeding, which may or may not have suckers.
    • Ampulla, a muscular sac that aids in the operation of tube feet.
  • Regeneration and Reproduction: Echinoderms have remarkable regenerative capabilities; many can regenerate lost parts and reproduce both asexually (via splitting) and sexually (by releasing gametes into the water).
Classifications within Echinoderms
  1. Asteroidea (Sea Stars): Most possess five or more arms; play a crucial role as predators in marine ecosystems.
  2. Echinoidea (Sea Urchins & Sand Dollars): Characterized by a lack of arms and double rows of tube feet, these creatures also feature protective spines.
  3. Ophiuroidea (Brittle Stars): This class is the largest among echinoderms; their arms are distinctively easy to tear off, a process known as autotomy.
  4. Crinoidea (Sea Lilies & Feather Stars): Often found attached to the sea floor, these echinoderms have feathery arms.
  5. Holothuroidea (Sea Cucumbers): Notable for their elongated bodies and leathery texture, these are also important in nutrient recycling in marine environments.

Phylum Chordata

Chordates have a distinct set of features relevant during some stage of their life cycle:

  • Notochord: A flexible rod that provides skeletal support.
  • Dorsal Hollow Nerve Cord: This structure eventually develops into the brain and spinal cord in vertebrates.
  • Pharyngeal Slits: Openings in the throat area that develop into gill structures in aquatic organisms or disappear in terrestrial ones.
  • Postanal Tail: Extending beyond the digestive tract's anus.
Subphyla of Chordata

Chordata is divided into three subphyla:

  1. Urochordata (Tunicates): Marine organisms with a sac-like body.
  2. Cephalochordata (Lancelets): Small, fish-like marine animals that retain chordate characteristics throughout their life.
  3. Vertebrata: Characterized by having a vertebral column, this subphylum includes all animals with a backbone.
Key Characteristics of Vertebrates
  • Vertebral Column: This bony structure encases the dorsal nerve cord and is a hallmark of vertebrate evolution.
  • Neural Crest: A unique group of embryonic cells that gives rise to various structures, including a significant part of the skull.
  • Endoskeleton: Composed of either cartilage or bone, facilitating size and movement.
Evolutionary History of Vertebrates

The first vertebrates emerged approximately 545 million years ago. They likely began as small, jawless fish-like creatures, evolving into various forms over time:

  • Jawed Fish (Chondrichthyes): Including sharks and rays, dominant predators of the Devonian period.
  • Ray-finned Fish (Actinopterygii): The most diverse vertebrate group currently, with over 30,000 species.
  • Lobed-finned Fish (Sarcopterygii): Ancestors of terrestrial vertebrates who evolved adapted structures for life on land.
Transition to Land: Amphibians and Reptiles
  • Amphibians: First vertebrates to conquer land, showing adaptations like legs and lungs but still reliant on water for reproduction.
  • Reptiles: Developed features such as amniotic eggs and scales, allowing for a more profound terrestrial existence, independent of water bodies for reproduction.
Class Mammalia

Mammals exhibit unique characteristics:

  • Hair: Provides insulation and sensory functions.
  • Mammary Glands: Allow females to nurse their young.
Subcategories of Mammals

Mammals are categorized into two main groups:

  1. Monotremes: Egg-laying mammals like the platypus.
  2. Therians: Include marsupials (like kangaroos) and placental mammals (most modern mammals) that give live birth.
Evolutionary Development of Primates

Primates, including humans, exhibit advanced features aiding in their survival in tree-dwelling environments. They are characterized by grasping fingers, binocular vision, and increased brain size—features that support complex social interactions and tool use.

Modern Human Evolution

Homo sapiens emerged around 600,000 years ago, showcasing significant brain development, use of tools, and complex social structures. The evolution of walking upright set the groundwork for the development of various cultures and advanced physical adaptations over time.

Questions for Study
  • Recognize the classifying traits of echinoderms and vertebrates.
  • Understand the evolutionary milestones in chordate and vertebrate history.
  • Differentiate between major groups within the deuterostomes and their unique features.