61.9.1.Deuterostomes

DEUTEROSTOMES

General Overview

  • Definition: Deuterostomes are a group of animals characterized by the development of the anus from the blastopore during embryonic development.

  • Key Characteristics:

    • Radial cleavage: During cell division, the embryonic cells align above each other.

    • Enterocoely: Coelom (body cavity) forms through outpocketing of the gut.

    • Bilateral symmetry: Adults exhibit bilateral symmetry in structure.

Major Groups of Deuterostomes

  1. Echinodermata (Phylum)

    • Common Name: Spiny-skinned animals.

    • Extant Species: Approximately 7,000.

    • Habitat: Mostly benthic marine environments.

    • Classes:

      • Asteroidea (sea stars)

      • Ophiuroidea (brittle stars)

      • Echinoidea (sea urchins and sand dollars)

      • Holothuroidea (sea cucumbers)

      • Crinoidea (sea lilies and feather stars)

    • Synapomorphies:

      • Pentaradial symmetry in adults

      • Endoskeleton made of calcareous plates

      • Mutable collagenous tissue

      • Water vascular system (a hydraulic system used for locomotion and feeding)

      • Capable of regeneration and autotomy (the ability to intentionally lose a limb).

  2. Hemichordata (Phylum)

    • Bilateral Symmetry: Display a more primitive bilateral symmetry.

    • Classes:

      • Enteropneusta (acorn worms, which are usually small, benthic, and can be solitary or colonial)

      • Pterobranchia (small colonial organisms that possess a U-shaped digestive tract).

  3. Chordata (Phylum)

    • Defining Synapomorphies:

      • Presence of a notochord

      • Dorsal hollow nerve cord

      • Pharyngeal gill pouches or slits

      • Endostyle (which may develop into thyroid gland)

      • Postanal tail

    • Subphylum Classifications:

      1. Urochordata (including tunicates)

      2. Cephalocordata (including lancelets)

      3. Vertebrata (including all vertebrates)

    • Evolutionary Notes:

      • The evolution of vertebrates includes the development of cranium and vertebral column, leading to advanced nervous and skeletal systems.

Differences between Deuterostome and Protostome Development

  • Blastopore Formation:

    • Protostomes: Blastopore becomes mouth, anus forms secondarily.

    • Deuterostomes: Blastopore becomes anus, mouth forms secondarily.

  • Cleavage Patterns:

    • Protostomes: Spiral cleavage.

    • Deuterostomes: Radial cleavage.

  • Coelom Formation:

    • Protostomes: Coelom forms by splitting (schizocoelous).

    • Deuterostomes: Coelom forms by outpocketing (enterocoelous).

  • Embryonic Development:

    • Protostomes: Mosaic embryo formation.

    • Deuterostomes: Regulative embryo formation.

Conclusion

  • The study of deuterostomes provides insights into the evolutionary lineage of complex organisms, particularly vertebrates, and helps comprehensively understand the physiological, anatomical, and developmental aspects within this broad grouping of animals.