BIOL 212 INVERTEBRATES BIOLOGY (MOVEMENT)

Movement in Animals

Locomotion in Animals

• Definition: Movement of an organism from one place to another; essential for searching food, water, shelter, and reproduction.

• Forms of Animal Movement: Varies from minor cytoplasmic streaming to vigorous striated muscle contractions.

• Mechanism: Relies on contractile proteins which change shape to elongate or contract.

  • Composed of:

    • Ultrathin fibrils (fine, striated, or tubular).

    • Powered by ATP.

Invertebrate Animals

• Definition: Animals without a backbone.

• Examples: Many types including:

  • Sponges, Corals, Jellyfish

  • Worms, Starfish, Sea Urchins

  • Mollusks (snails, octopuses)

  • Arthropods (insects, spiders, crabs)

• Muscle Attachment: Varies across invertebrates; for instance, arthropods attach muscles to a rigid chitinous exoskeleton.

Forms of Invertebrate Locomotion

1. Amoeboid Movement

   • Mechanism: Exhibited by amoeba; involves flowing cytoplasm creating projections known as pseudopodia.

   • Process:

     • Cytoplasm flows into bulges, forming pseudopodia which enables crawling effectively at about 5µm/s.

     • Plasma membrane has adhesive properties that stick to substrates helping in movement.

2. Movement by Fibrils

   • In protozoans, seen in:

     • Cilia: Numerous small hair-like structures that beat to move the organism.

     • Flagella: Longer, whip-like tail used for locomotion (e.g., Euglena).

   • Speed: Organisms using fibrils can move at speeds of 20-200µm/s.

3. Ciliary Movement

   • Involves cilia moving in coordinated strokes to propel the organism.

   • Characteristics of Stroke:

     • Effective strokes occur when cilia are parallel to body surface.

     • Recovery strokes are slower and bent out of phase, allowing the maneuverability of movement.

4. Hydrostatic Skeleton Movement

   • Uses incompressible fluid to maintain body shape and facilitate movement (e.g., in earthworms).

   • Muscle arrangements: Circular & longitudinal muscles contract antagonistically to enable movement.

5. Limbs and Legs Movement

   • Arthropods and other invertebrates utilize rigid skeletal structures to support and enable movement.

   • Walking mechanisms in terrestrial environments involve jointed elements allowing for flexion and extension.

Muscular System of Invertebrates

• Functional differences from vertebrates exist: e.g., arthropods may have multiple motor nerve inputs per muscle fiber.

• Muscles operate antagonistically; thus, contraction on one side necessitates the opposite reaction to produce movement.

Locomotion in Various Invertebrates

1. Jellyfish: Utilize mesogloea for propulsion through jet propulsion methods.

2. Platyhelminthes (flatworms): Display looping and gliding movement via their muscular systems and hydrostatic skeleton.

3. Molluscs: Gastropods move using a muscular foot and employ ciliary action in small forms.

4. Arthropods: Centipedes and millipedes utilize a more complex gearing system to run, showcasing variations in energy expenditure for locomotion.

   • Centipedes: Carnivorous, fast with top gear use.

   • Millipedes: Herbivorous, slow-moving with bottom gear use.

Evolution of Limbs

• Evolution from primitive parapodia in polychaetes to legs in arthropods shows adaptation to various locomotor strategies.

• Leg movement is categorized by different "gears" indicating speed:

  • Bottom Gear: Movement is slow when legs are mostly on the ground.

  • Middle Gear: Equal protraction and retraction speed.

  • Top Gear: Leg off ground, rapid movement.

Wing Movement in Insects

• Structure of Wings: Membranous and supported by veins.

• Mechanics: Utilize synchronous or asynchronous muscles for wing movement.

• Energy Usage: High demand for energy and oxygen, managed via spiracles and tracheae.

• Types of Muscle:

  • Synchronous: Contraction tied to nervous impulses.

  • Asynchronous: Contract faster than nerve impulses come, allowing rapid movement.