1. Body Cavity:

• Acoelomate
• Pseudocoelomate
• Coelomate

Acoelomate

No body cavity between gut and outer covering.

Pseudocoelomate

Body cavity partially lined with mesoderm.

Coelomate

Body cavity fully lined with mesoderm.

Segmentation:

• Division into repeated segments that may contain organs/structures

Animal Kingdom Subdivisions

1. Subkingdom Parazoa: Only sponges, lack true tissues.
2. Subkingdom Eumetazoa: All other animals, with true tissues.

Subkingdom Parazoa - Phylum Porifera

• Organization: Cellular level (no true tissues or organs).
• Body Plan: Sac type with one opening.
• Symmetry: Asymmetrical.
• Reproduction: Mostly hermaphroditic; capable of sexual and asexual reproduction (budding or fragmentation).
• Feeding: Filter feeders using specialized cells: choanocytes and amoebocytes

Choanocytes (Collar Cells)

Create water currents with flagella, trap and digest particles.

Amoebocytes

Transport nutrients, remove wastes, and store food in the mesohyl layer.

Class Calcarea

Calcium carbonate spicules.

Class Demospongiae

Spongin fibers; most flexible (80% of sponges).

Class Hexactinellida

Silica spicules, often glass-like.

subkingdom eumetazoa

• Cnidaria
• Ctenophora
• Platyhelminthes
• rotifera
• Arthropoda
• Nematoda
• Mollusca
• Annelida:

Phylum Cnidaria

Coelenterata.

• Tissues: True tissues present.
• Mesoglea: Jelly-like layer between the epidermis and gastrodermis.
• Symmetry: Radial symmetry.
• Nervous System: Non-centralized nerve nets.
• Digestion: Food is brought into a gastrovascular cavity for extracellular digestion; nutrients absorbed via phagocytosis.
• Specialized Cells: Cnidocytes containing nematocysts (stinging cells).
• Body Plan: Sac-like.

classes of cnidaria

hydrozoa

scyphozoa

cubozoa

anthozoa

Class Hydrozoa:

• Dominant Stage: Polyp.
• Examples: Obelia (colonial organism).
• Reproduction: Medusa stage, if present, used for sexual reproduction. Larvae are called planula.

Class Scyphozoa:

• Common Name: True jellyfish.
• Dominant Stage: Medusa.

Class Cubozoa:

• Common Name: Box jellies, sea wasps.
• Notable Species: Chironex fleckeri (highly venomous).

Class Anthozoa:

• Stage: Only polyp stage.
• Includes: Corals and sea anemones.
• Function: Coral skeletons build reefs; some have symbiotic relationships with dinoflagellates (zooxanthellae).

Phylum Ctenophora

• Common Name: Comb jellies (due to eight comb rows).
• Characteristics:
• Radial symmetry.
• Largest animals using cilia for locomotion.
• Tissue level of organization.

• Protostomes:

• Blastopore becomes the mouth.
• Determinate cleavage.
• Spiral cleavage.
• Mesoderm arises from splitting of endoderm.
• Coelom arises from splitting of solid mesoderm

• Deuterostomes:

• Blastopore becomes the anus.
• Indeterminate cleavage.
• Radial cleavage.
• Mesoderm arises from outpocketings of the endoderm wall.
• Coelom forms as a cavity in a pouch of mesoderm.

Phylum Platyhelminthes Flatworms.

• Characteristics:
• Branched gastrovascular cavity.
• Digestion is both intracellular and extracellular.
• No circulatory or respiratory systems.
• Excretion via flame cells in protonephridia.
• Triploblastic (three germ layers) and acoelomate.
• Organ level of organization.
• Body is dorsally flattened.
• Type: Protostome.

classes of Platyhelminthes

Class Turbellaria

Class Trematoda

Class Cestoda

Class Turbellaria:

• Includes: Planaria.
• Features:
• Mostly free-living.
• Light-sensitive regions (eyespots).
• Capable of primitive learning.

Class Trematoda

Fluke.

• Characteristics:
1. All members are parasites, either endoparasitic (internal) or ectoparasitic (external).
2. May have complex life cycles involving multiple hosts

Class Cestoda

Tapeworm.

• Characteristics:
1. Head region is called the scolex.
2. Body is composed of repeating packets of reproductive organs called proglottids.
3. Can have two or more hosts.
4. Absorbs nutrients directly across its body surface from the host's digestive tract.

Phylum Rotifera Rotifers (meaning "wheel bearers")

• Characteristics:
1. Cell constant: all members of a species have the same number of cells.
2. Loss of cells is not compensated by mitosis.
3. Possess jaws called trophi for grinding food.
4. Can reproduce via parthenogenesis (development of eggs without fertilization).
5. Multicellular, exhibiting bilateral symmetry and triploblastic organization.

Phylum Nematoda

Roundworms

• Characteristics:
1. Have only longitudinal muscles.
2. Can be free-living or parasitic.
3. Found in diverse habitats, including soil, freshwater, marine environments, and inside plants and animals.
4. Hydrostatic skeleton.
5. Examples include Trichinella (from undercooked pork), hookworms, pinworms, and filarial worms (causative agent of elephantiasis).
6. Exhibit bilateral symmetry and triploblastic organization.

Phylum Nemertea

Ribbon or proboscis worms

• Characteristics:
1. Have a complete digestive tract (one-way system).
2. Possess a simple circulatory system.
3. Triploblastic and bilateral symmetry.
4. Muscle present, with a tube-in-tube body plan.
5. Classification is debated between coelomate and pseudocoelomate, but currently considered coelomate.

Phylum Mollusca

• Characteristics:
• Common Features:
1. Mantle: Tissue fold covering the visceral mass.
2. Muscular foot: Used for movement.
3. Visceral mass: Contains internal organs.
4. Radula: A conveyor belt of teeth for feeding.
5. Calcium carbonate shell: Present in some, reduced or absent in others.
• Second largest animal phylum (after Arthropoda), with diverse habitats.
• Most species are separate sexes; some are hermaphrodites (e.g., certain snails).
• Triploblastic and possess all major organ systems.

Classes within Mollusca

1. Class Polyplacophora:
2. Class Gastropoda:
3. Class Bivalvia:
4. Class Scaphopoda:
5. Class Cephalopoda:

Class Polyplacophora

Common Name: Chitons. Characteristics: Shell segmented; not segmented body.

Class Gastropoda

Includes: Snails, whelks, slugs, nudibranchs.

Characteristics: Mantle vascularized for gas exchange; torsion observed during development.

Class Bivalvia

Includes: Clams, oysters, mussels, scallops.

Characteristics: No radula; filter feeders; shell divided into two halves.

Class Scaphopoda

Common Name: Tooth shell (resembling canine teeth).

Class Cephalopoda

Includes: Octopi, squid, chambered nautilus, cuttlefish.

• Foot modified into a siphon and tentacles.
• Only mollusks with a closed circulatory system.
• Capable of complex behaviors and learning.

Phylum Annelida (Segmented Worms)

• Characteristics:
1. Each segment contains distinct organs.
2. Has closed circulatory system and hydrostatic skeleton

classes of Phylum Annelida

• Class Oligochaeta (Earthworms)
  Class Polychaeta (Marine Worms)
  Class Hirudinea (Leeches)

Phylum Onychophora (Velvet Worms)

• Characteristics:
• Exhibit traits of both Annelida and Arthropoda.

Phylum Arthropoda

• Characteristics:
1. Largest animal phylum with jointed appendages.
2. Exoskeleton made of chitin.
3. Open circulatory system and hemocoel

subphylums of Phylum Arthropoda

• Subphylum Trilobitomorpha
1. All extinct.

Subphylum Cheliceriformes
Subphylum Myriapoda
Class Chilopoda (Centipedes)

Class Diplopoda (Millipedes)

Characteristics:

• Commonly known as millipedes.
• Herbivorous diet.
• Possess two pairs of walking legs per segment.
• Among the earliest land animals.

Subphylum Pancrustacea

• Includes diverse groups such as crustaceans and insects.

Subphylum Hexapoda (Insects)

• Body divided into three regions: head, thorax, and abdomen.
• Mouthparts modified for chewing, sucking, or lapping.
• Typically have three pairs of legs and two pairs of wings (wings are extensions of the cuticle).
• Mostly terrestrial.

Class Insecta Specific Features:

• Front legs modified into mandibles.
• Possess one or two pairs of antennae and compound eyes.
• Inhabit almost all terrestrial habitats (rarely found in marine environments).
• Many species evolved during the Cretaceous period alongside flowering plants.
• Mouthparts consist of a pair of mandibles, a pair of maxillae, and a labium (lower lip).
• Legs and wings are attached to the thorax; mating structures are located on the abdomen.
• Use malpighian tubules for excretion.
• Gas exchange occurs through a tracheal system.
• Internal fertilization occurs, with two types of metamorphosis

Complete Metamorphosis:

egg → larva → pupa → adult (e.g., butterfly).

Incomplete Metamorphosis:

egg → nymph → adult (e.g., grasshopper)

Selected Orders of Insecta:

• Coleoptera
• Hymenoptera
• Hemiptera
• Lepidoptera
• Diptera
• Orthoptera
• Siphonaptera
• Isoptera
• Homoptera
• Phasmatodea
• Phtiraptera

Coleoptera

Beetles & weevils

Hymenoptera

Wasps, bees, hornets

Hemiptera

True bugs, assassin bugs, bed bugs

Lepidoptera

Butterflies & moths

Diptera

True flies & mosquitoes

Orthoptera

Grasshoppers, crickets, katydids

Siphonaptera

Fleas

Isoptera

Termites

Homoptera

Cicadas & aphids

Phasmatodea

Walking sticks

Phtiraptera

Human body louse

Subphylum Crustacea

Characteristics:

• Includes crabs, shrimp, crayfish, krill, sow bugs, pill bugs, barnacles, and lobsters.
• Body composed of two or three parts.
• Crustaceans are the only arthropods with two pairs of antennae.
• Mouthparts are adapted for chewing.
• Typically have three or more pairs of legs.
• Mostly found in marine and freshwater environments; some are terrestrial.
• Have appendages on the abdomen, unlike insects.