Key Concepts of Arthropoda, Deuterostomia, and Chordata

Phylum Arthropoda

• Body plan:

  • Segmented body

  • Hard exoskeleton

  • Made of chitin

  • Molting necessary for growth

  • Paired, jointed appendages

• 3 major lineages:

  • Chelicerates

  • Myriapods

  • Pancrustaceans

Chelicerates

• Examples include:

  • Scorpion

  • Dust mite

  • Web-building spider

• Size reference:

  • Scorpions can be approximately 50 μm in size.

Myriapods

• Examples include:

  • (a) Millipede

  • (b) Centipede

Insects and Pancrustaceans

• Common ancestor of arthropods:

  • Includes the following groups:

  • Remipedians (a crustacean group)

  • Other crustaceans

  • Myriapods (includes insects and crustaceans)

  • Chelicerates

Crustaceans

• Include:

  • Lobsters

  • Crabs

  • Shrimp

  • Pill bugs

  • Barnacles

• Characteristics:

  • Many have highly specialized appendages

  • Walking legs located on thorax

  • Swimming appendages located on the tail

Insects

• Body structure:

  • Divided into three regions:

  • Head

  • Thorax

  • Post-genital region

• Internal organ system:

  • Complex and well-developed

• Wings:

  • Are extensions of the cuticle

Complete Metamorphosis

• Stages include:

  • (a) Larva (caterpillar)

  • (b) Pupa

  • (c) Later-stage pupa

  • (d) Emerging adult

  • (e) Adult

Deuterostomia

• Includes:

  • Phylum Echinodermata (sea stars and sea urchins)

  • Phylum Chordata (invertebrates and vertebrates)

• Key characteristics:

  • Radial cleavage

  • Blastopore forms the anus

Echinodermata

• General traits:

  • Slow-moving marine coelomates

  • Spiny covering on endoskeleton

  • Water vascular system branches into tube feet

  • Bilaterally symmetrical larvae

Major Classes of Echinoderms

• Holothuroidea

• Ophiuroidea

• Crinoidea

• Echinoidea

• Asteroidea

Ancestral Deuterostome

• Key features:

  • Notochord present

  • Common ancestor of chordates

  • Various vertebrate features such as jaws, mineralized skeleton, and lungs or lung derivatives

• Lineages include:

  • Echinodermata

  • Cephalochordata

  • Urochordata

  • Myxini

  • Petromyzontida

  • Chondrichthyes

  • Actinopterygii

  • Actinistia

  • Dipnoi

  • Lobed fins

  • Amphibia

  • Limbs with digits

  • Reptilia

  • Amniotic egg

  • Mammalia

  • Milk

• Key terms to understand:

  • Chordates include both vertebrates and two groups of invertebrates

Derived Characters of Chordates

• Key characteristics:

  • Notochord

  • Dorsal, hollow nerve cord

  • Post-anal tail

  • Pharyngeal slits or clefts

  • Muscular segments

Lancelets (Cephalochordata)

• Characteristics include:

  • Cirri

  • Mouth

  • Pharyngeal slits

  • Atrium

  • Digestive tract with Atriopore

  • Notochord

  • Dorsal, hollow nerve cord

  • Segmental muscles

  • Tail

  • Size: Approximately 1 cm

  • Description: Small, fish-like invertebrate chordates; marine suspension feeders

Tunicates (Urochordata)

• Characteristics include:

  • Notochord

  • Dorsal, hollow nerve cord

  • Tail

  • Excurrent siphon

  • Muscle segments

  • Incurrent siphon

• Water flow:

  • Water flows through the incurrent siphon to mouth, then out through the excurrent siphon

• Internal Anatomy:

  • Atrium

  • Pharynx with numerous slits

  • Intestine

  • Stomach

  • Anus

• Life Cycle Stages:

  • (a) A tunicate larva

  • (b) An adult tunicate

  • (c) An adult tunicate (commonly referred to as sea squirts)

Vertebrates

• Definition:

  • Chordates with a backbone

• Key features:

  • Well-developed skeletal system

  • A complex nervous system makes vertebrates efficient at capturing food and evading prey

Jawless Vertebrates

• Examples include:

  • Hagfish

  • Lamprey

Gnathostomes

• Definition:

  • Vertebrates that have jaws with teeth

• Groups included:

  • Sharks

  • Rays

  • Ray-finned fishes

  • Lobe-finned fishes

  • Tetrapods

Tetrapods

• Characteristics:

  • Gnathostomes with limbs

  • Derived characters include:

  • Four limbs and feet with digits

  • A neck

  • Fusion of pelvic girdle to backbone

  • Absence of gills (except in some aquatic species)

  • Ears

Amphibians

• Body characteristics:

  • Most have moist skin that functions in gas exchange

  • Eggs lack a shell, with external fertilization in most

  • Many amphibians live both in water and on land

Amniotes

• Definition:

  • Tetrapods that have a terrestrially adapted egg (amniotic egg)

• Components include:

  • Amnion

  • Chorion

  • Yolk sac

  • Allantois

• Groups included:

  • Reptiles (including birds)

  • Mammals

Reptiles

• Included types:

  • Dinosaurs

  • Turtles

  • Lizards

  • Snakes

  • Crocodiles

  • Birds

• Derived characters:

  • Dry skin with scales

  • Lay shelled eggs on land

  • Internal fertilization

Birds

• Bone structure includes:

  • Finger 1: Wing

  • Forearm

  • Wrist

  • Shaft

  • Vane

  • Finger 2

  • Finger 3

Mammals

• Definition:

  • Amniotes that have hair and produce milk

• Other derived characters include:

  • Kidneys

  • Endothermic

  • Efficient respiratory and circulatory systems

• Major lineages include:

  • Monotremes

  • Marsupials

  • Eutherians (placental mammals)

Monotremes

• Definition:

  • Egg-laying mammals

• Examples:

  • Spiny anteater

  • Duck-billed platypus

• Lactation:

  • Milk secreted from glands on belly

Marsupials

• Definition:

  • Include pouched mammals

• Examples:

  • Kangaroos

  • Opossums

• Reproductive characteristics:

  • Born early in development and finish growing while nursing from nipple in marsupium

Eutherians (Placental Mammals)

• Major characteristics:

  • Complex placenta

  • Complete development within the uterus, joined to the mother by the placenta