Animal Systematics

Systematics

• The study of biological diversity and classification

• classification of living organisms by evolutionary relationship

Classification

• Carolus Linnaeus (1707-1778) – Swedish naturalist

• Developed the modern taxonomic classification system

Linnean System of Classification

KingdomPhylumClassOrderFamilyGenusSpecies

AnimaliaChordata

MammaliaPrimates

HominidaeGorilla

Gorilla gorilla

Revised Linnean SystemDivision KingdomPhylum

SubphylumSuperclass

ClassSubclassInfraclass

OrderSuperfamily

FamilySubfamily

GenusSpecies

Subspecies

EukaryaAnimaliaChordata

VertebrataTetrapodaMammalia

Theria EutheriaPrimates

AnthropoideaHominidaePonginaeGorilla

Gorilla gorillaGorilla gorilla beringei

Binomial Nomenclature

• Genus + species• Examples:

– Rana catesbeiana: bull frog– Turdus migratorius: American robin– Homo sapiens: modern human– Mucosa domestica: house fly

• Subspecies sometimes included– Gorilla gorilla beringei: mountain gorilla

What is an Animal

• Eucaryotic – cells divided into organelles

• Multicellular• Heterotrophic

– do not produce own nutrients• Lack cell walls• Tissues linked by proteins (e.g. collagen)

What is an Animal

• Cells often linked by cell junctions– gap, adhesion, tight

• Possess electrogenic cells – nerve cells and muscle cells

• Reproduce sexually (diploid)– sperm + egg → zygote → blastula → gastrula

→ larva → adult

Major Evolutionary Divergences Among Animals

• Development of Tissues• Development of Body

Plans• Development of Body

Cavities• Developmental Origin

of the Coelom

Development of Tissues

• Development of aggregations of similar cells into patterns and layers

• Parazoa (sponges) – lack tissues• Eumetazoa – possess tissues

Development of Body Plans

• Pattern of body and structure• Number of embryonic cell layers• Radiata (e.g. jellyfish, hydra)

– radial symmetry– diploblastic (2 germ cell layers)

• Bilatera (everything else)– Blateral symmetry– Triploblastic (3 germ cell layers)

Development of Body Cavities

• Acoleomates (flatworms)– no body cavities

• Pseudocoelomates (rotifers, roundworms)– body cavity not surrounded by

mesoderm (pseudocoelom)• Coleomates (everything else)

– body cavity enclosed by mesoderm (coelom)

Developmental Origin of the Coelom

• Coelomates are divided into two gorups based upon:

1. Pattern of cell cleavage during early development

2. When cell developmental fate is determined3. How the coelom is formed4. How the digestive tract is formed during

gastrulation

Protostomes

• Mollusks, earthworms, insects, etc.• Spiral cleavage

– cell division diagonal to vertical axis

• Determinant cleavage– development into tissues determined

very early in cleavage

• Schizocoelous– coelom forms by splitting solid

masses of mesoderm in

• Blastopore forms mouth

Deuterostomes• Starfish, vertebrates• radial cleavage

– cell division at right angles to vertical axis

• indeterminant cleavage– development into tissues determined

later in cleavage• enterocoelous

– coelom forms by mesoderm layer budding from archenteron

• blastopore forms anus

Parazoa:Phylum Porifera

• sponges• little cell differentiation• sessile • no nerve or muscle cells• porous body

– enables water circulation through the body

– flow driven by choanocytes– food collected and digested

by amoebocytes

Radiata:Phylum Cnidaria

• Corals, jellyfish, anemones, corals

• gastrovascular cavity– central compartment

with single opening• two basic body plans:

– polyp – usually sessile– medusa – motile form

Radiata:Phylum Cnidaria

• tentacles arranged around opening to the gastrovascular cavity

• lined with nematocysts– stinging cells

• possess nerve cells forming nerve net– no central nervous system

• possess muscle-like cells

Radiata:Phylum Ctenophora

• Comb jellies• Similar in appearance to

jellyfish• Possess comb-like plates

of cilia used for locomotion

• Collect food with tentacles covered with colloblasts (lasso cells)

Acoelomates:Phylum Platyhelminthes

• Flatworms• gastrovascular cavity with one

opening• true muscle tissue• primitive excretory system (water

balance)• sensory organs in head

(photoreceptors, chemoreceptors)• central nervous system (ganglia in

head w/ ventral nerve cords)

Acoelomates:Phylum Platyhelminthes

• Major Classes– Turbellaria

• planarians (free living)– Monogenea and

Tremotoda• flukes (parasites)

– Cestoidea • tapeworms (parasites)

Pseudocoelomates:Phylum Rotifera

• Rotifers• complete digestive tract

– separate mouth and anus• pseudocoelomic fluid

acts as circulatory system

• cilia lining crown draw water into the mouth

Pseudocoelomates:Nematoda

• Nematodes (roundworms)• complete digestive tract• pseudocoelomic fluid acts

as circulatory system• longitudinal muscle

orientation• aquatic habitats, soils,

plant and animal parasites

Protostome Coelomates:Phylum Nemertea

• Proboscis worms• acoelomous body, except for

fluid-filled sac used to extend proboscis

• similar excretory, sensory and nervous systems to flatworms

• complete digestive tract• closed circulatory system

(blood confined to vessels)

Protostome Coelomates:Lophophorate Phyla

• possess lophophore– ciliated fold around

mouth• no head• U-shaped digestive

tract

Protostome Coelomates:Lophophorate Phyla

• Bryozoans – sessile, resemble

moss, hard exoskeletons

• Phoronids – horseshoe worms

• Brachiopods– resemble bivalves

Protostome Coelomates:Phylum Mollusca

• Mollusks• Major Classes:

– Class Polyplacophora• chitons

– Class Gastropoda • snails and slugs

– Class Bilvalvia • clams, oysters, mussels, etc.

– Class Cephalopoda• octopus, squid, nautiluses

Protostome Coelomates:Phylum Mollusca

• Muscular foot• visceral mass

– contains organs• gills (respiration)• complete digestive tract w/

specialized organs• open circulatory system

(blood not confined to vessels)• mantle

– covers visceral mass, secretes shell

Protostome Coelomates:Phylum Annelida

• Annelids (segmented worms)• hydrostatic skeleton• coelom in repeating segments

with alternating longitudinal and circular muscles, setae, and metanephridia (excretion)

• closed circulatory system• several specialized regions in

digestive tract• cerebral ganglia with ventral

nerve cord

Protostome Coelomates:Phylum Annelida

• Major Classes– Class Oligochaeta

(earthworms)– Class Polychaeta

(polychaetes)– Class Hirudinea

(leeches)

Protostome Coelomates: Phylum Arthropoda

• specialization of body segments– specialized limbs, etc.

• hard exoskeleton– protein and chitin

• high cephalization of sensory organs

• open circulatory systems– blood (hemolymph) not

confined to vessels

Arthropods:Chelicerates

• claw-like feeding appendages (chelicerae), lack antennae

• Class Arachnida (spiders, scorpions, ticks, mites)– 2 body segments (cepahlothorax and

abdomen)– 6 pairs of appendages

• chelicerae, pedipalps, 4 pr walking legs extend from cephalothorax

– book lungs• enhances gas exchange btw hemolymph

and air

Arthropods:Uniramians

• jaw-like feeding appendages (mandibles), 1 pair of antennae, unbranched appendages

• Class Diplopoda – millipedes • Class Chilopoda – centipedes• Class Insecta – insects

– three body segments (head, thorax, abdomen)

– many possess wings– specialized digestive system– Malpighian tubules (excretion)– tracheal system (respiration)

Arthropods:Crustaceans

• mandibles, 2 pair of antennae, branched appendages

• Class Crustacea– possess gills– salt glands (hemolymph salt

balance)• Groups

– Isopods (e.g. pill bugs)– Copepods (e.g. Cyclops)– Decapods (crabs, lobsters, etc.)

Deuterostome Coelomates :Phylum Echinodermata

• sea stars, sea urchins, sea cucumbers

• adults have radial symmetry– bilateral larvae

• endoskeleton of hard plates

• water vascular system– used to manipulate tube

feet

Deuterostome Coelomates :Phylum Chordata

• Lancelets tunicates, vertebrates• Characteristics of embryos:

1. possess notochord• longitudinal, flexible rod between

digestive tract and nerve cord2. possess dorsal hollow nerve

cord3. have pharyngeal slits

• modified for gas exchanges, jaw support, hearing, etc.

4. have muscular postanal tail

Invertebrate Chordates

• Subphylum Urochordata– tunicates– sessile marine animals– chordate characters seen

only in larvae• Subphylum

Cephalochordata – lancelets

Subphylum Vertebrata• Characteristics

– neural crest formation during embryonic development

– vertebral column + skull– pronounced cephalization of sensory and neural

apparati– closed circulatory system

• Agnathans– lack hinged jaws, notochord present throughout life

• Gnathostomes– possess hinged jaws, notochord replaced by

vertebrae, paired appendages• Tetrapods

– Possess two pairs of appendages

Superclass Agnatha

• lack hinged jaws,• notochord present

throughout life• no paired appendages• lampreys and hagfish

Superclass Gnathostoma:Jawed Fish

• Class Chondrichthyes– Sharks, rays– cartilaginous skeletons

• Class Osteichthyes – bony fish (bone skeletons)– Subclass Actinopterygii

• Ray-finned fish

– Subclass Sarcopterygii• Lobe-finned fish

Superclass Tetrapoda:Class Amphibia

• Characteristics– tetrapods (4 limbs)- terrestrial

movement– aquatic larval stage– moist, permeable skin

• Anurans– frogs and toads

• Urodeles– salamanders and newts

• Caecilians– legless, fossorial amphibians

Superclass Tetrapoda:Class (?) Reptilia

• Reptiles• Scaly, impermeable skin• Amniotes

– Lay shelled amniotic eggs• Chelonians (Testudines)

– Turtles• Lepidosaurians

– Tuatara, snakes, lizards• Archosaurs

– Crocodilians, dinosaurs, birds

Superclass Tetrapoda:Class Aves

• Birds• Amniotes• Possess feathers• Possess wings (flight)• Endothermic

– most body heat generated internally

• Two-circuit circulatory system

Superclass Tetrapoda:Class Mammalia

• Mammals• Possess hair• Possess mammary glands• Endothermic• Two-circuit circulatory system• Most give birth to young

(amniotic)• Diaphragm for active ventilation

of lungs

Superclass Tetrapoda:Class Mammalia

• Groups– Monotremes

• lay eggs • platypuses, echidnas

– Marsupials• embryo completes development in

pouch • kangaroos and opossums

– Eutherians • form placenta• cats, humans, squirrels