Animal Diversity

Overview of Animal Phyla

Phylum Porifera (Sponges)

• Characteristics:

  • Asymmetrical body structure

  • Sister group to sessile organisms

  • Lack true tissues

• Feeding:

  • Filter feeders

• Classification:

  • Monophyletic group: Eumetazoa (animals with symmetry)

Eumetazoa

• True tissues leading to more specialization

• Types of Symmetry:

  • Radial symmetry: multiple symmetrical planes

  • Bilateral symmetry: single symmetrical plane

Phylum Ctenophora

• Characteristics:

  • Radial symmetry

  • Eight rows of cilia called "combs"

  • Some species possess tentacles

Phylum Cnidaria (Jellies, Hydras, Anemones, Corals)

• Characteristics:

  • Radial symmetry

  • Body plans: Polyp and Medusa

  • Stinging cells (cnidocytes)

  • Gastrovascular cavity with tentacles

• Life Cycle:

  • Alternation of generations (e.g., Obelia: asexual polyps, sexual medusa)

Subphyla of Cnidaria

Subphylum Anthozoa (Corals and Anemones)

• Only polyp form (no medusa stage)

• Corals:

  • Characteristics: exoskeleton housing polyps

  • Symbiotic relationship with algae (zooxanthellae) providing glucose to corals

Subphylum Medusozoa

• Must have both polyp and medusa forms

Developmental Biology

• Embryonic development in animals:

  1. Cleavage: formation of a blastula (hollow sphere of cells)

  2. Gastrulation: formation of the gut

  3. Alimentary canal development: leads to mouth and anus

• Classification:

  • Protostome: mouth forms first

  • Deuterostome: anus forms first

Phylum Echinodermata

• Characteristics:

  • Spiny skin (calcium carbonate)

  • Water vascular system

  • Oral surface known for numerous functions

Phylum Chordata (Vertebrates and Relatives)

• Key Features:

  • Notochord as a primary support structure

  • Dorsal hollow nerve cord (precursor to the central nervous system)

  • Muscular post-anal tail for movement

  • Pharyngeal gill slits: gas exchange and filter feeding

Superphylum Lophotrochozoa

• Characteristics:

  • Presence of lophophores (tentacles with cilia)

Phylum Platyhelminthes (Flatworms)

• Characteristics:

  • Flat body structure for increased surface area

• Classifications:

  • Class Cestoda: Tapeworms

  • Class Trematoda: Flukes (e.g., freshwater)

Phylum Syndermata

• Included Groups:

  • Rotifers and Acanthocephalans (spiny-headed worms)

Phylum Mollusca

• General Structure:

  • If a shell is present, it is secreted by a mantle

• Common Classes:

  • Class Bivalvia: Clams, mussels, scallops

  • Class Gastropoda: Snails, slugs (characterized by torsion)

  • Class Cephalopoda: Squids, octopuses

Phylum Brachiopoda

• Unique Features:

  • Symmetrical vs. asymmetrical shells (bivalves vs. brachiopods)

  • Pedicel (stalk) supporting the body

  • Lophophore for feeding

Phylum Annelida

• Characteristics:

  • Body divided into segments by septa

• Classifications:

  • Class Oligochaeta: Earthworms

  • Class Polychaeta: Marine worms

  • Class Hirudinea: Leeches

Superphylum Ecdysozoa

• Features:

  • Cuticle made of chitin, molted during ecdysis

Phylum Nematoda (Roundworms)

• Characteristics:

  • Tapered ends, many free-living and some parasitic

  • Important decomposers

Phylum Arthropoda

• Largest phylum:

  • Jointed appendages, includes insects, crustaceans, arachnids

  • Subphyla:

    • Subphylum Chelicerata: Characteristics of chelicerae and pedipalps with book gills/lungs

Subphyla under Arthropoda

Subphylum Myriapoda

• Includes centipedes and millipedes

Subphylum Crustacea

• Includes insects as well as aquatic forms

Phylum Chordata - Key Features

• Synapomorphies of Chordates:

  • Notochord, dorsal hollow nerve cord, pharyngeal slits, post-anal tail

Subphylum Cephalochordata (Lancelets)

• Features:

  • First to diverge from other chordates

  • Burrow in sediment and suspension feed

Subphylum Urochordata (Tunicates)

• Characteristics: become sessile as adults, covered by a tunic

Subphylum Vertebrata

• Characteristics:

  • Possess a head and sensory organs

  • More active lifestyle requiring muscles for movement

Early Vertebrates

• Metaspriggina: Cambrian jawless fish

• Class Myxini (Hagfishes): Cartilaginous skull, no jaws, retains notochord for life, has slime glands for defense.

• Class Petromyzontida (Lampreys): Cartilaginous structures, retains notochord, partially protects nerve cord.

Jawed Vertebrates (Gnathostomes)

• Characteristics:

  • Development of jaws, more fins, originated in aquatic environments

  • Types of fins:

    • Median fins (dorsal, anal)

    • Paired fins (pectoral, pelvic) modified into limbs in tetrapods

Class Elasmobranchii (Sharks and Rays)

• Characteristics:

  • Cartilaginous skeleton, which evolved from ancestors with bony structures

Class Actinopterygii (Ray-finned Fish)

• Features:

  • Bony skeleton, swim bladder present for buoyancy

Class Sarcopterygii (Lobed-finned Fish)

• Unique Structures:

  • Muscular fins, some can breathe air via lungs alongside gills

Transition to Land (Tetrapods)

• Adaptations for land:

  • Limbs with digits, adaptation of respiratory systems

  • Key fossils from the Devonian period highlight transitions

Class Amphibia

• Unique Features:

  • Glandular skin, requires water for reproduction; external fertilization

  • Eggs lack shells for environmental exchange

Amniotes

• Adaptations allowing less dependence on water for reproduction

• Features of the Amniotic Egg:

  • Leathery shell for support

  • Amnion: protects embryo in a fluid-filled cavity

  • Chorion: gas exchange

  • Allantois: metabolic waste disposal and gas exchange

  • Yolk sac: nutrient storage

Reptiles

• Important Groups:

  • Tetrapods with lungs and scales

  • Archosaurs: ruling reptiles including birds, crocodiles, and others

Mammalia

• Key Characteristics:

  • Hair and mammary glands for nurturing young

• Subdivisions:

  • Monotremes: egg-laying mammals (e.g., echidna, platypus)

  • Marsupials: pouch-bearing mammals

  • Eutherians: placental mammals allowing extended embryonic development in utero.