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The Animal Kingdom

The Coelomate Protostomes

  • Classification in the animal kingdom.

Higher Invertebrates

  • Focus on three phyla:

    • Mollusca

    • Annelida

    • Arthropoda

  • Known as Higher Invertebrates due to the presence of a coelom.

Overview of Invertebrate Phyla

  • Distinct phyla include:

    • Sponges

    • Cnidarians

    • Flatworms

    • Nematodes

    • Mollusks

    • Annelids

    • Arthropods

    • Echinoderms

    • Chordates

Phylum Mollusca

  • About 50,000 species.

  • Second largest animal phylum.

  • Includes:

    • Classes considered:

      • 4 out of 7 total classes.

    • Members include: oysters, clams, mussels, scallops, snails, slugs, squids, octopuses, nautiluses.

  • Habitat: present in saltwater, freshwater, and land.

  • Body Structure:

    • Bilaterally symmetrical with varying shapes and sizes.

      • Sizes range from 1mm clams to 21-meter squids.

Common Characteristics of Mollusks

  • General features include:

    • Visceral Mass: Soft-bodied portion containing internal organs.

    • Muscular Foot: A strong muscular structure for movement.

    • Mantle: A fold of skin that surrounds the body organs and secretes the shell in shelled species.

Circulatory System and Reproduction

  • Open circulatory system where blood bathes the internal organs directly.

  • Free-swimming larval stages include:

    • Trochophore – develops into

    • Veliger larva with a shell and foot.

  • Some feed on crops:

    • Snails and slugs can be destructive to agriculture.

Classification of Mollusks

  • Class Polyplacophora:

    • Chitons with a shell of 8 plates.

  • Class Gastropoda:

    • Includes snails and slugs;

    • Unique radula for feeding.

    • Can retract into shells.

  • Class Bivalvia:

    • Composed of clams and oysters with two-part shells.

    • Filter feeders handling food using siphons.

  • Class Cephalopoda:

    • Includes squids and octopuses, known for their intelligence and mobility.

    • Closed circulatory system with advanced nervous systems.

Phylum Annelida

  • Contains approximately 15,000 species.

  • Body segmented by septa, allowing for improved locomotion.

  • Found in diverse environments.

  • Classes of Annelids:

    • Class Polychaeta: Marine segmented worms with parapodia.

    • Class Oligochaeta: E.g., earthworms; important for soil health.

    • Class Hirudinea: Leeches, often bloodsuckers with specialized anatomy.

Phylum Arthropoda

  • Comprising around 1 million species.

  • Distinct features include an exoskeleton, jointed appendages, segmented bodies, and a complex nervous system.

  • Adaptations for survival in various environments, including land and water.

  • Subphylum Classes:

    • Class Insecta: Largest group, known for flight and adaptability.

    • Class Arachnida: Spiders and scorpions, noted for their predatory habits.

    • Class Crustacea: Includes crabs and lobsters, primarily marine animals.

Phylum Echinodermata

  • Known for spiny skin, includes starfish and sea cucumbers.

  • Unique Aspects:

    • Radial symmetry in adults, bilateral in larvae.

    • Water vascular system facilitates movement and feeding in sea stars.

    • Capable of regeneration.

Conclusion

  • The animal kingdom encompasses a diverse range of organisms classified into numerous phyla, each with unique features and ecological roles. Understanding these classifications aids in comprehending biodiversity and evolutionary relationships.