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A Tour of Animal Diversity

Objectives

Students should be able to:

• Compare and contrast invertebrates and vertebrates in terms of their characteristics, physiology, and ecological roles.

• Recognize and describe body symmetry as a key feature in classification and adaptation.

• Identify major anatomical features of the following representative animals:

  • Sponges: Basic multicellular organisms with porous structures.

  • Hydra (Cnidarian): A simple animal with stinging cells found in fresh water.

  • Planarians (Flatworm): Notable for their ability to regenerate lost body parts and their flat, elongated shape.

  • Mussels (Mollusk): Bivalve mollusks that play important roles in ecosystems as filter feeders.

  • Earthworms (Annelid): Essential for soil aeration and nutrient cycling; exhibit segmentation.

  • Crayfish (Arthropod): An important aquatic invertebrate with a complex exoskeleton that provides protection and structure.

  • Grasshoppers (Arthropod, Insect): Exhibits adaptations for flight and jumping, playing a unique role in ecosystems as herbivores.

  • Sea stars (Echinoderm): Marine organisms characterized by their unique water vascular system used for movement and feeding.

  • Bony fishes (Vertebrate, bony fish): Notable for their evolutionary adaptations such as a swim bladder and streamlined bodies.

  • Frogs (Vertebrate, amphibian): Known for their life cycle involving metamorphosis from aquatic tadpoles to terrestrial adults.

  • Snakes (Vertebrate, reptile): Adapted for a carnivorous diet with various means for hunting and locomotion.

  • Rats (Vertebrate, mammal): Highly adaptable mammals with complex social behaviors and high learning abilities.

• Classify an unknown animal into one of these groups based on morphological and anatomical evidence.

Introduction

Diversity of Animals

The animal kingdom boasts more than 2 million species that have been identified, showcasing a vast diversity of body forms, sizes, and ecological niches found across all major habitats, including terrestrial, aquatic, and aerial environments. Understanding this diversity is crucial for exploring biological functions, evolutionary relationships, and ecosystem dynamics.

Common Characteristics of All Animals

• Eukaryotic Cells: All animals are composed of eukaryotic cells that contain a nucleus and organelles.

• Multicellular Structure: Animals are composed of multiple cells organized into tissues, which serve specialized functions.

• Heterotrophic Metabolism: Animals cannot produce their own food; they must consume organic material to obtain energy and sustain cellular functions.

• Absence of Cell Walls: Unlike plants and fungi, animal cells lack rigid cell walls, allowing for greater flexibility and interaction between cells.

• Movement Capability: While movement varies, all animals possess the capability of movement at some developmental stage, whether through locomotion or internal movement of cells.

Body Structure

Cells form tissues that work together to perform specific functions, such as digestion, movement, and reproduction.

Symmetry

Animal bodies exhibit symmetry, which can be categorized into three main types:

• Radial Symmetry: Symmetrical arrangement around a central axis, allowing for the organism to be divided into similar halves through multiple planes (e.g., sea stars).

• Bilateral Symmetry: A distinct left and right side that mirror each other, enabling directional movement and complex body structures (e.g., humans).

• Asymmetry: Organisms that lack symmetrical forms and do not conform to standard symmetry (e.g., most sponges).

Body Symmetry

Radial Symmetry

Characteristics include body parts arranged around a central axis. Example: Sea stars show radial symmetry in their adult form, facilitating interaction with their environment.

Bilateral Symmetry

Creatures with distinct left and right body halves, allowing for complex organ arrangements and enhanced mobility.

Anatomical Orientation

• Anterior (front)

• Posterior (back)

• Dorsal (top)

• Ventral (bottom)

Classification of Animals

Invertebrates

Invertebrates are animals without a backbone and make up approximately 95% of all animal species, displaying vast diversity.

Vertebrates

Vertebrates are characterized by the presence of a backbone, comprising a smaller proportion of the animal kingdom yet exhibiting remarkable complexity and adaptability.

Purpose of the Lab

The lab aims to investigate the morphological and anatomical characteristics of various representative animals (both invertebrates and vertebrates) to accurately classify unknown specimens and understand their ecological and biological significance.

Procedure

1. Observe representative animal specimens in a guided classroom examination.

2. Draw each specimen and label the important anatomical structures observed.

3. Complete the classification table on page 5 based on the observed features.

Animal Observations

Sponges

• Definition: Simple organisms with numerous pores and canal systems; lack true tissues and specialized cells.

• Lifestyle: Filter feeders, maintaining water flow through incurrent pores and releasing it through a central osculum.

Hydra (Cnidarian)

• Forms: Exists in two forms: as a polyp (stationary) and a medusa (free-floating); hydra examples primarily demonstrate the polyp form.

• Features: Possesses specialized stinging cells (cnidocytes) which are utilized for capturing and immobilizing prey.

Planarian (Flatworm)

• Characteristics: Notable for regeneration capabilities, enabling them to regrow lost parts and survive in hostile environments; typically possesses a flattened and elongated body structure.

• Sensory Organs: Includes two eyespots that are sensitive to light, aiding in navigation and environmental awareness.

Mussel (Mollusk)

• Anatomy: Characterized by a robust external shell made of calcium carbonate; body enclosed within two shells (valves) that are hinged together.

Earthworm (Annelid)

• Structure: Exhibits a segmented body plan with a clear bilateral symmetry; crucial for soil aeration and nutrient cycling in terrestrial habitats.

Crayfish (Arthropod)

• Definition: A highly diverse group distinguished by their hard exoskeleton and jointed appendages; inhabit freshwater environments.

• Body Regions: The body is divided into cephalothorax and abdomen, equipped with multiple appendages for locomotion and feeding.

Grasshopper (Arthropod, Insecta)

• Diversity: Highly varied, representing the most diverse group of animals in terms of species count and ecological roles.

• Body Structure: Divided into three segments: head, thorax, and abdomen; features include wings and hind legs adapted for jumping.

Sea Star (Echinoderm)

• Symmetry: Exhibits radial symmetry as adults and bilateral symmetry as larvae, displaying significant morphological changes through development.

• Anatomy: Comprises five arms, equipped with tube feet that facilitate movement, prey capture, and respiration.

Amphioxus (Chordate)

• Importance: Serves as a critical evolutionary link between invertebrates and vertebrates; a model organism for developmental biology.

• Characteristics: Possesses key features like pharyngeal gill slits, a notochord, dorsal hollow nerve chord, and post-anal tail, fundamental for vertebrate development.

Vertebrates (Perch, Frog, Snake, Rat)

• Characteristics: All vertebrates possess an endoskeleton; exhibit features concluded from evolutionary history for increased size and mobility such as:

  • Cephalization: Concentration of sensory organs at the anterior end, enabling complex behaviors.

  • Vertebral Column with a Cranium: Provides support and protection for the central nervous system.

  • Circulatory and Respiratory Systems: Complexity varies among species, enhancing survival across diverse environments.

• Classes: Seven classes of vertebrates exist (3 are fishes while 4 are tetrapods), showcasing diverse adaptations that enable terrestrial life.

Classification Table (Example from Page 5)