Untitled

• Summarized notes on animal evolution, characteristics, and various phyla

Animal Evolution and Characteristics

• The earliest animals emerged approximately 700 million years ago
• Multicellularity was a crucial evolutionary shift in animal development
• Early animal fossils date back to 560 million years ago during the Ediacaran Period

Defining Characteristics of Animals

• Eukaryotic
• Multicellular
• Heterotrophic: obtains nutrients by ingesting and internally digesting food
• Possesses no cell walls, and uses collagen for adhesion

Evolutionary Milestones

• Prokaryotes first appeared 3.5 billion years ago in the Archean Era
• Eukaryotes emerged 1.8 billion years ago in the Protozoic Era
• The first multicellular organism emerged 1.2 billion years ago in the Protozoic Era
• The Cambrian explosion marked a significant increase in animal diversity

Body Plan Symmetry

• Animals exhibit different symmetry types
• Asymmetry: lacking a defined symmetry
• Radial symmetry: symmetry around a central axis
• Bilateral symmetry: having a left and right side

Embryonic Development

• Two primary developmental pathways involve the formation of complex germ layers: ectoderm, endoderm, and mesoderm
• Protostome development: Spiral cleavage, with cell fate determined early, and the blastopore becomes the mouth; solid masses of mesoderm form the coelom (e.g., mollusks and annelids)
• Deuterostome development: Radial cleavage, with undetermined cell fate, and the blastopore becomes the anus; the mesoderm folds of the archenteron to form the coelom (e.g., echinoderms and chordates)

Body Cavities

• Acoelomate: lacking a body cavity, with tissue filling the space
• Pseudocoelomate: having a "false" body cavity, where the mesoderm and endoderm are not connected
• Coelomate: possessing a true body cavity, where the mesoderm and endoderm connect, aiding in nutrient, gas, and waste transport, providing structural support, cushioning organs, and allowing independent organ growth

Germ layers

• Diploblastic: having two germ layers, the endoderm and ectoderm
• Triploblastic: having three germ layers, including the endoderm, ectoderm, and mesoderm

Phylum Porifera - Sponges

• Suspension feeders: capture food particles suspended in water
• Water flow is critical for survival; choanocytes capture food particles suspended in water; water enters through the spongocoel and pores, exiting through the osculum
• Cellular processes involve phagocytosis as the primary method of food absorption; amebocytes distribute nutrients throughout the sponge's body
• Spongin is a protein that comprises the sponge's "skeleton"
• Capable of producing both sperm and egg cells
• Spiky spicules that provide protection

Phylum Ctenophora - Comb Jellies

• Diploblastic: two germ layers
• Radial symmetry
• Structural features include eight rows of cilia for movement and two tentacles with colloblasts to capture prey
• Modified gastrovascular cavity and a nerve net enable sensation and response to stimuli; contractile tissue aids movement
• Evolutionary tree suggests its emergence around 770 million years ago

Phylum Cnidaria - Corals, Jellies, Sea Anemones

• Diploblastic: possess two germ layers
• Radial Symmetry
• Contractile tissue and a nerve net for movement and sensation
• Possess a gastrovascular cavity for digestion
• Specialized stinging cells (nematocytes) capture prey

Phylum Platyhelminthes - Flatworms

• Triploblastic: possessing three germ layers
• Acoelomate: lacking a body cavity
• Exhibit cephalization with a primitive brain
• Capable of regeneration and can be free-living or parasitic

Phylum Mollusca - Snails and Slugs

• Features a hemocoel containing hemolymph
• Open circulatory system
• Possesses a complete digestive tract
• Consists of a foot, visceral mass, and mantle
• Often has a calcium carbonate covering for protection
• Contains a radula, a specialized spiky tongue

Phylum Annelida - Segmented Worms

• Larger coelom
• Complete digestive tract
• Closed circulatory system (primarily blood)
• Segmentation
• Circular and longitudinal muscles to allow movement

Phylum Nematoda - Roundworms

• Hemocoel facilitates the movement of gases and food
• Lacks a circulatory system
• Protective cuticle to keep from dehydration
• Complete digestive tract
• Ecdysis occurs for growth
• Only longitudinal muscles
• Can be free-living or parasitic

Phylum Arthropoda - Insects, Crustaceans

• Small coelom and a large hemocoel
• Displays the highest amount of species diversity
• Cuticle comprised of exoskeleton
• Ecdysis
• Jointed appendages
• Segmentation into head, thorax, and abdomen
• Myriapods consist of centipedes and millipedes
• Chelicerates consist of arachnids and horseshoe crabs
• Pancrustaceans consist of crustaceans and insects

Phylum Echinodermata - Sea Stars and Sand Dollars

• Deuterostome development
• Larvae are bilateral, while adults are semi-radial
• Features an endoskeleton with spines that build up the internal skeleton
• Employs a water vascular system for gas and nutrient transfer
• Utilizes tube feet for movement

Phylum Chordata

• Key characteristics:
  • A notochord provides skeletal support
  • A dorsal hollow nerve cord develops into the central nervous system
  • Pharyngeal slits/clefts develop into gills or ears
  • A post-anal tail extends beyond the digestive tract

Invertebrate Chordates

• Lancelets have basic chordate features
• Tunicates, also known as sea squirts, exhibit chordate features as larvae

Vertebrae Development

• Gradual increase
• Neural crest contributes to skull, teeth, and nervous system
• Backbone replaces the notochord
• Increasing specialization

Vertebrate Chordates

• Hagfish and lampreys
• Cartilaginous fish lack a minimized skeleton, have non-covered gills (e.g., sharks, skates, and rays)
• Boney fish which have a flap over the hills
• Lungs derived trait that is a swim bladder

Amphibians

• Earliest tetrapods
• Tied to water
• Must stay moist for gas exchange (e.g., frogs, salamanders, and caecilians)

Amniotes

• Eggs have extraembryonic membranes designed for protection
• Hard outer shell

Reptiles

• Diapsids have two holes behind the eye socket where jaw muscles come into contact
• Shelled eggs

Birds

• No bladder, no teeth, hollow bones, a 4-chamber heart, and large and efficient lungs

Mammals

• Synapsids have one hole behind their eye socket
• Have hair/fur
• Endothermic
• Teeth different size & shape
• Have mammary glands and milk
• Have a 4 chambered heart and efficient lungs

Mammals - Monotremes

• Egg laying mammals
• The most primitive extant mammals are the echidnas and platypus
• Lacks nipples with mammary glands

Mammals - Marsupials

• Placenta provides food, oxygen, and nourishment
• Nipple provide milk for offspring

Mammals - Eutherian

• More complex placenta
• Have more Complex embryonic development in uterus
• Nipple provides milk

Mollusca Subclasses

• Gastropoda possess feet, eyes, tentacles, radula, shell, snails, and slugs
• Bivalva possess shells, adductor muscles, bivalves, and oysters
• Cephalopoda possess brains, big head, arms, and tentacles

Arthropoda Subclasses

• Crustaceans consist of a segmented body, exoskelleton, crabs, and lobsters
• Myropoda: wingless, many-legged
• Chelicerata: Chitinous exoskelleton, Segmented abdomen, spiders, horshoe crab, mites
• Insects exoskelleton, wings, 3 body segments, jointed appendages, 6 legs, and fl