Animal Diversity, Structure, and Function: Study Notes

Animal Diversity

What is an Animal?

Animals are multicellular, heterotrophic eukaryotes whose cells develop into tissues from embryonic layers. They are defined by a combination of characteristics that distinguish them from other life forms.

• Heterotrophic: Animals obtain energy by ingesting other organisms.

• Multicellularity: Composed of multiple cells with specialized functions.

• Tissues: Groups of similar cells acting as functional units; unique to animals are nervous and muscle tissue.

Nutritional Mode

• Animals are efficient consumers, using adaptations to detect, capture, eat, and digest food.

• They ingest food, unlike fungi (which absorb) or plants (which photosynthesize).

Cell Structure and Specialization

• Animal cells lack cell walls; instead, they are supported by structural proteins like collagen.

• Tissues are collections of specialized cells separated by membranes.

• Nervous and muscle tissue are defining features of animals.

Reproduction and Development

• Most animals reproduce sexually; the diploid stage dominates the life cycle.

• After fertilization, the zygote undergoes cleavage (rapid cell division), forming a blastula (hollow ball of cells).

• The blastula undergoes gastrulation, forming a gastrula with embryonic tissue layers.

Body Plans and Symmetry

• Animals are categorized by body symmetry, tissue layers, body cavities, and developmental modes.

• Symmetry:

  • Radial symmetry: Body parts arranged around a central axis (e.g., jellyfish).

  • Bilateral symmetry: Distinct left/right, dorsal/ventral, anterior/posterior (e.g., humans).

• Tissue Layers:

  • Diploblastic: Two layers (ectoderm and endoderm).

  • Triploblastic: Three layers (ectoderm, mesoderm, endoderm).

• Body Cavities:

  • Coelomate: True body cavity (coelom) from mesoderm.

  • Pseudocoelomate: Body cavity from mesoderm and endoderm.

  • Acoelomate: No body cavity.

• Functions of Body Cavities:

  • Cushion organs, act as hydrostatic skeleton, allow organ movement.

Protostome vs. Deuterostome Development

• Protostome: Spiral, determinate cleavage; mouth develops from blastopore.

• Deuterostome: Radial, indeterminate cleavage; anus develops from blastopore.

• Indeterminate cleavage allows for identical twins and embryonic stem cells.

Introduction to Invertebrates

Overview

• Invertebrates: Animals without a backbone; over 95% of animal species.

• Highly diverse, occupying nearly every habitat.

Phylum Porifera (Sponges)

• Basal animals lacking true tissues.

• Support: Spicules (calcium carbonate/silica) and spongin fibers.

• Filter feeders; water flows through pores into the spongocoel, out the osculum.

• Hermaphroditic, often sequentially.

Structure	Function
Mesohyl	Gelatinous matrix between cell layers
Epidermis	Outer cell layer
Pores	Entry points for water
Spongocoel	Central cavity
Choanocytes	Flagellated cells for water flow and food capture
Amoebocytes	Transport nutrients, produce skeletal fibers

Phylum Cnidaria

• Includes jellies, corals, hydras; diploblastic, radial symmetry.

• Body plan: Sac with gastrovascular cavity (single opening).

• Two forms: Polyp (sessile) and Medusa (motile).

• Carnivorous; use cnidocytes (stinging cells) with nematocysts (stinging organelles).

Group	Examples	Notes
Medusozoans	Jellies, box jellies, hydrozoans	Produce medusa stage; some highly toxic
Anthozoans	Corals, sea anemones	Only polyp stage; corals form symbiosis with algae

Phylum Platyhelminthes (Flatworms)

• Marine, freshwater, terrestrial; many are parasites (flukes, tapeworms).

• Acoelomates; gastrovascular cavity with one opening.

Phylum Syndermata (Rotifers and Acanthocephalans)

• Rotifers: Tiny, mostly aquatic; have alimentary canal; reproduce by parthenogenesis.

• Acanthocephalans: Sexually reproducing parasites of vertebrates.

Phylum Ectoprocta and Brachiopoda

• Ectoprocta: Sessile, colonial, moss-like appearance.

• Brachiopoda: Resemble clams, have hinged shells.

Phylum Mollusca

• Soft-bodied, often with calcium carbonate shell.

• Body plan: Muscular foot (movement), visceral mass (organs), mantle (may secrete shell).

• Feed with radula (scraping organ).

Class	Examples
Polyplacophora	Chitons
Gastropoda	Snails, slugs
Bivalvia	Clams, oysters
Cephalopoda	Squids, octopuses, cuttlefish, nautiluses

Phylum Annelida

• Segmented worms (coelomates) with bodies of fused rings.

• Major groups: Errantia (mobile) and Sedentaria (less mobile).

Phylum Nematoda

• Roundworms; found in diverse habitats.

• Cylindrical, tapered ends; no circulatory system; undergo ecdysis (molting).

Phylum Arthropoda

• Segmented body, jointed appendages, exoskeleton of protein and chitin.

• Most diverse animal phylum; found in nearly all habitats.

Phylum Echinodermata

• Sea stars, sea urchins, etc.; slow-moving or sessile marine animals.

• Bilateral larvae, five-part adult body plan, unique water vascular system, endoskeleton.

Vertebrate Diversity

What is a Vertebrate?

• Animals with a backbone (vertebrae).

• Over 57,000 species, including the largest animals on Earth.

• Great diversity in form and function.

Phylum Chordata

• Bilaterian animals; includes all vertebrates and two invertebrate groups: Urochordates and Cephalochordates.

Key Characteristics of Chordates

• Notochord: Flexible rod for skeletal support; replaced by vertebral column in most adults.

• Dorsal, hollow nerve cord: Develops into brain and spinal cord.

• Pharyngeal slits/clefts: Grooves in pharynx; function in feeding, gas exchange, or develop into head/neck structures.

• Muscular, post-anal tail: Provides propulsion in aquatic species; reduced in many adults.

Subphyla of Chordates

Subphylum	Key Features	Examples
Cephalochordata	Retain chordate features as adults	Lancelets
Urochordata	Chordate features in larval stage; adults are sessile filter feeders	Tunicates (sea squirts)
Myxini	Jawless, cartilaginous skull, produce slime	Hagfishes
Petromyzontida	Jawless, parasitic or free-living, cartilaginous skeleton	Lampreys
Chondrichthyans	Cartilaginous skeleton	Sharks, rays, chimeras
Actinopterygii	Ray-finned, bony fish	Most familiar fish
Sarcopterygii	Lobe-finned fish	Coelacanths, lungfish
Tetrapods	Four limbs, neck, fused pelvic girdle, ears	Amphibians, reptiles, mammals

Basic Principles of Animal Form and Function

Anatomy vs. Physiology

• Anatomy: Biological form of an organism.

• Physiology: Biological function.

• Form and function are closely correlated.

Animal Tissues

• Epithelial: Covers body, lines organs/cavities; shapes: cuboidal, columnar, squamous; arrangements: simple, stratified, pseudostratified.

• Connective: Binds/supports; types: loose, fibrous (tendons, ligaments), bone, adipose, blood, cartilage.

• Muscle: Movement; types: skeletal (voluntary), smooth (involuntary), cardiac (heart).

• Nervous: Receives, processes, transmits information; neurons and glial cells.

Body Control: Endocrine vs. Nervous System

• Endocrine: Hormones released into bloodstream; slow, long-lasting effects.

• Nervous: Fast, specific signal transmission via neurons.

Heat Exchange and Thermoregulation

• Organisms exchange heat by: radiation, evaporation, convection, conduction.

• Homeostasis: Maintaining internal balance; involves set point, sensors, control center, and response.

• Thermoregulation: Keeping internal temperature within a normal range.

Energy Requirements and Metabolic Rate

• Bioenergetics: Flow and transformation of energy in an animal.

• Animals are heterotrophs; require chemical energy from food.

• Metabolic rate: Total energy used per unit time; measured by heat loss, O2 consumption, CO2 production, or food/waste energy content.

Animal Nutrition

Overview

• Animals are herbivores (plants/algae), carnivores (animals), or omnivores (both).

• Diet must provide: chemical energy, organic building blocks, and essential nutrients.

Essential Nutrients

• Cannot be synthesized by the animal; must be obtained from diet.

• Four classes: essential amino acids, essential fatty acids, vitamins, minerals.

Food Processing: Four Steps

1. Ingestion: Eating/feeding.

2. Digestion: Breaking down food (mechanical and chemical).

3. Absorption: Uptake of small molecules by cells.

4. Elimination: Removal of undigested material.

Feeding Mechanisms

• Filter feeders: Sift particles from water (e.g., sponges).

• Substrate feeders: Live in/on food source (e.g., caterpillars).

• Fluid feeders: Suck fluids from hosts (e.g., mosquitoes).

• Bulk feeders: Eat large pieces of food (e.g., humans).

Mammalian Digestive System

• Accessory glands: salivary glands, pancreas, liver, gallbladder.

• Secrete digestive juices into alimentary canal.

Circulation and Gas Exchange

Open vs. Closed Circulatory Systems

• Both have circulatory fluid, vessels, and a heart.

• Open: Hemolymph bathes organs directly (e.g., insects, some molluscs).

• Closed: Blood confined to vessels, distinct from interstitial fluid (e.g., annelids, vertebrates).

Closed Circulatory System: Vessels

• Arteries: Carry blood away from heart to capillaries.

• Capillaries: Sites of exchange with tissues.

• Veins: Return blood to heart.

Single vs. Double Circulation

• Single: Blood passes through heart once per circuit (e.g., fish).

• Double: Blood passes through heart twice (pulmonary and systemic circuits; e.g., mammals, birds, amphibians).

Path of Blood Flow in Mammals

• Right ventricle → pulmonary arteries → lungs (O2 uptake, CO2 release) → pulmonary veins → left atrium → left ventricle → systemic circulation.

Respiratory System

• Air pathway: nostrils → pharynx → larynx → trachea → bronchi → bronchioles → alveoli.

• Gas exchange occurs in alveoli.

• Cilia and mucus trap and remove particles.

The Immune System

Pathogens and Defense

• Pathogens: Disease-causing agents (bacteria, viruses, fungi, parasites, toxins).

• Immune system cells interact with and destroy pathogens.

Innate vs. Adaptive Immunity

Feature	Innate Immunity	Adaptive Immunity
Presence	All animals/plants	Vertebrates only
Speed	Immediate	Slower, after innate
Barriers	Skin, mucous membranes	Bone marrow, spleen, lymph nodes, thymus

Lymphatic System

• Lymph: Fluid lost by capillaries, returned to circulation by lymph vessels.

• Lymph nodes: Filter lymph, house immune cells.

• Lymph organs: Adenoids, tonsils, thymus, spleen, Peyer’s patches, appendix.

Primary vs. Secondary Immune Response

• Primary: First exposure to antigen; slower response, formation of lymphocyte clones.

• Secondary: Faster, more efficient response due to memory cells.