Animal Biology and Classification Notes

Animals

Definition of Animals

• Multicellular eukaryotes

• Heterotrophs (organisms that ingest their own food)

• Distinguished by:

  • Body symmetry (asymmetry, radial, bilateral)

  • Number of embryonic tissue layers (diploblasts vs. triploblasts)

  • Presence/absence of a body cavity (coelomates, pseudocoelomates, acoelomates)

  • Patterns of early embryonic development

• Species exhibit diverse body plans and adaptations across various habitats.

Major Taxonomic Groups of Animals

• Animal Phyla:

  • Choanoflagellates

  • Porifera (sponges)

  • Cnidaria (corals, jellyfish, sea anemones)

  • Ctenophora

  • Acoelomorpha

  • Rotifera

  • Platyhelminthes (flatworms)

  • Protostomes: Lophotrochozoa, Ecdysozoa

  • Deuterostomes: Annelida, Mollusca, Nematoda, Arthropoda, Echinodermata, Chordata

Types of Body Symmetry

• Asymmetry: No definite shape (e.g., sponges)

• Radial symmetry: Multiple planes of symmetry (e.g., sea anemones)

• Bilateral symmetry: One plane of symmetry leading to left and right halves (e.g., lizards)

Early Embryonic Development and Germ Layers

• Ectoderm: Forms the skin and nervous system

• Mesoderm: Develops into muscles, connective tissue, skeleton, kidneys, and circulatory/reproductive organs

• Endoderm: Creates lining of gut and organs derived from it

Body Plans and Tissue Layers

• Acoelomate: No coelom (body cavity), only digestive cavity.

• Pseudocoelomate: Partially developed coelom, digestive cavity present.

• Eucoelomate: True coelom; digestive cavity and body cavity are present and separate.

Gamete Formation and Fertilization

• Gametes: Sperm and egg produced in gonads (testes and ovaries) via meiosis.

• Fertilization: Egg (n) + sperm (n) = diploid zygote (2n).

• Fertilization membrane prevents additional sperm from fertilizing the egg.

Fertilization Methods

• Internal Fertilization:

  • Occurs within the female body; requires more energy and results in fewer offspring.

• External Fertilization:

  • Typically occurs in water; produces many gametes susceptible to environmental conditions; aims for high fertilization probability.

Classification of Animals

• Sponges (Porifera):

  • Lack distinct body plan and tissues.

  • Filter feeders using ostia for water intake and osculum for water outflow.

Cnidarians

• Body Features:

  • Radial symmetry, diploblastic (two tissue layers).

  • Possess tentacles with cnidocytes (stinging cells) for prey capture.

  • Exhibit polyp (sessile) and medusa (motile) forms.

Protostomes

• Definition:

  • Embryonic development involves a mouth developing from the blastopore.

  • Characterized by bilateral symmetry and cephalization.

  • Triploblastic with division of labor through organ systems.

Major Lineages of Protostomes

• Lophotrochozoa:

  • Includes Platyhelminthes, Annelida, and Mollusca.

• Ecdysozoa:

  • Includes arthropods and nematodes.

Platyhelminthes (Flatworms)

• Groups: Free-living planarians, parasitic flukes, and tapeworms.

• Body is acoelomate and lacks a true body cavity.

• Incomplete digestive system with gastrovascular cavity.

Annelida (Segmented Worms)

• Features:

  • Eucoelomate, metameric body structure with segmentation.

  • Complete digestive tract functioning throughout the segmented body.

Mollusca (Mollusks)

• Main Groups: Chitons, gastropods, bivalves, cephalopods.

• Eucoelomate with complete digestive tract and diverse anatomical features like the radula (except bivalves).

Earthworm Anatomy

• Must know region-specific structures:

  • Pharynx

  • Hearts

  • Seminal vesicles

  • Seminal receptacles

  • Esophagus

  • Crop

  • Gizzard

  • Dorsal blood vessel

  • Intestine

• Note: Relate these to their respective organ systems (digestive, reproductive, cardiovascular) for practical exams!