23. Ecdysozoa

UNIVERSITY OF ALBERTA BIOL 108

  • Introduction to Biological Diversity

  • Lecture A2 - Yan-yin Wang

Introduction to Ecdysozoa

  • Source: Campbell et al. (2024)

  • Key Characteristics:

    • True tissues

    • Bilateral symmetry

    • Triploblastic germ layer

  • Clade Bilateria:

    • Contains Lophotrochozoa, Ecdysozoa, and Deuterostomia

  • Ecdysozoa:

    • Monophyletic group recovered by molecular phylogenetic analyses

    • Comprises eight phyla, phylogenetic relationships among them are unclear

    • Prominent phyla include Nematoda and Arthropoda

Shared, Derived Traits of Ecdysozoans

  • Source: Becker et al. (2018)

  • Cuticle in Ecdysozoans:

    • Covers bodies and is periodically moulted

    • Composed of tough, non-living organic material, primarily chitin (glycosamine polymer)

  • Functions of the Cuticle:

    • Provides mechanical protection

    • Acts as a barrier against desiccation

    • Forms exoskeleton for structural support

Anatomy of the Cuticle

  • Layers of Cuticle:

    • Procuticle: Contains chitin

    • Endocuticle: Innermost layer

    • Exocuticle: Middle layer

    • Epicuticle: Thin, waxy, water-resistant outer layer; lacks chitin

  • Variability in Composition:

    • Arthropods exhibit sclerotisation, producing hardened cuticle components (sclerites)

    • Only specific regions of cuticle undergo sclerotisation, leading to armor plates and flexible regions for mobility

Ecdysis

  • Definition: Process of shedding the entire cuticle to allow growth

  • Significance:

    • Allows for regeneration of damaged tissues (e.g., missing limbs)

    • Facilitates removal of external parasites

Process of Ecdysis

  • Steps of Ecdysis (8 Steps):

    1. Apolysis: Inactivity, separation of old cuticle from epidermis

    2. Moulting Fluid Secretion: Inactive enzymes secreted to facilitate peeling

    3. New Proto-Epicuticle Formation: Deposited on epidermis for initial protection

    4. Activation of Moulting Fluid: Digests old endocuticle and aids in new cuticle buildup

    5. Reabsorption of Moulting Fluid: Ensures nutrients are utilized for new cuticle

    6. New Epicuticle Deposition: Protects underlying structures

    7. Moulting of Old Cuticle: May involve swallowing air to aid the process

    8. Sclerotisation of New Cuticle: Final stages where sclerotisation of the new cuticle occurs

Reflective Questions for Exam Preparation

  • What are the basic layers of cuticle?

  • Describe the process of ecdysis.

  • Can some of the moulting steps be considered adaptive? Why?