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Introduction To Animals
The Invertebrates
Introduction
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What is an Animal: five criteria,
(1) Animals are multicellular, heterotrophic eukaryotes.
(2) Animal cells lack cell walls that provide structural
supports for plants and fungi.
(3) Animals have two unique types of tissues: nervous
tissue for impulse conduction and muscle tissue for
movement.
(4) Most animals reproduce sexually, with the diploid
stage usually dominating the life cycle
(5) The transformation of a zygote to an animal of
specific form depends on the controlled expression
in the developing embryo of special regulatory genes
called Hox genes.
Most Animal
Reproduction
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The larva - sexually immature stage that is
morphologically distinct. Think Butterfly!!
Metamorphosis
 Complete and Incomplete
Animal Origins
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animal kingdom is
monophyletic.
Likely a colonial flagellated
protist that lived over 700
million years ago in the
Precambrian era.
Hello Cousin!!!
Ideas
Universal Genes have let us understand
just how easy diversification would have
been.
DIVERSITY
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35 phyla of animals
phylogenetic tree is always under construction
in the light of new evidence
the molecular evidence of the past decade has
challenged some of these long-held ideas about
phylogenetic relationships
When Did Animals Diversify
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The Cambrian Explosion
This lasted about 40 million years (about 565 to 525
million years ago)
Nearly all the major animal body plans appear in
Cambrian rocks
Fossilized animal embryos in China - 570 mya
Fossilized burrows from rocks 1.1 bya.
Molecular evidence suggests the origin of
multicellular animals to be approx. 1 bya
Diversification
3 main hypotheses for what caused the
diversification of animals.
(1) Ecological Causes: predator-prey relationships
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(2) Geological Causes: Atmospheric oxygen
(3) Genetic causes: Hox genes within the embryo.
The Universality of these body building genes is
astounding!!!!!
Invertebrates
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Over 1.6 million extant species of animals
Our sense of animal diversity is biased in favor
of vertebrates,
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less than 2% of all animal species.
98% of all species are Inverts.
Estimate between 5 and 100 million species of
animals on earth.
(Parazoa)
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Phylum Porifera: sponges
closest to the colonial choanoflagellates
Made of a loose federations of cells
Sessile animals
Lack nerves or muscles.
9,000 or so species of sponges range in height
from about 1 cm to 2 m and most are marine.
About 100 species live in fresh water.
Suspension feeders
Sponges Cont…
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2 cell layers separated by a gelatinous region,
the mesohyl.
Wandering though the mesohyl are
amoebocytes.
 They take up food from water and from
choanocytes.
 secrete tough skeletal fibers within the
mesohyl.
Fibers are either sharp spicules of calcium
carbonate or silica or flexible fibers from a
collagen protein called spongin
Sponges Cont..
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Most sponges are
hermaphrodites
Some use fragmentation.
capable of extensive
regeneration
Eumetazoa (Radiata)
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Includes Cnidaria and Ctenophora
Cnidarians (hydras, jellies, sea anemones, and
coral animals)
10,000 living species, most of which are
marine.
Gastrovascular cavity
2 variations: the sessile polyp and the
floating medusa.
Cnidarians Cont..
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Cnidarians are carnivores
Have cnidocytes for feeding and defense.
 Cnidae shoot out a thread
 Cnidae called nematocysts are stinging
capsules
Muscles and nerves exist in their simplest
forms in cnidarians.
Know all 3 classes!
3 Classes of Cnidaria
Phylum Ctenophora
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Comb Jellies
Ctenophora means “comb-bearer”
Have a pair of long retractable tentacles.
 These tentacles armed with (colloblasts)
Bilateria (Protostomia)
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2 clades: Lophotrochozoa and Ecdysozoa
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Lophotrochozoa is made up of 6 phyla:
Platyhelminthes, Rotifera, Lophophorates
(Bryozoans Phoronida, & Brachiopods),
Nemertea, Mollusca, and Annelida
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Ecdyzoan has 2 phyla: Nematoda and
Arthropoda
Platyhelminthes
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Platyhelminthes: Acoelomates with
gastrovascular cavities
20,000 species of flatworms living in marine,
freshwater, and damp terrestrial habitats
 many parasitic species, flukes and
tapeworms.
Size from nearly microscopic to tapeworms
over 20 m long
Triploblastic
Flatworms are divided into four classes:
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Turbellaria, Monogenia, Trematoda, and Cestoidea
Cont…
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Turbularians: Ex. Planarians,
are carnivores or scavengers in unpolluted
ponds and streams.
lack organs specialized for gas exchange and
circulation, wastes are removed by diffusion,
move using cilia,
has a head with a pair of eyespots to detect
light
lateral flaps that function mainly for smell,
can learn to modify their responses to stimuli,
reproduce asexually through regeneration
The Monogeneans& Trematodes
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(class Monogenea) and
the trematodes live as
parasites in or on other
animals.
 Many have suckers
 A tough covering
protects the parasites.
 Reproductive organs
nearly fill the interior of
these worms.
 The fluke Schistosoma
infects 200 million
people
Class Cestoidea
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Tapeworms
 parasitic.
 The adults live mostly
in vertebrates
 scolex anchor the
worm in the digestive
tract of the host.
A long series of
proglottids
Ultimate parasite
Phylum Rotifera
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1,800 species
tiny animals (0.05 to 2 mm),
most of which live in freshwater
have a complete digestive tract
pseudocoelom, a body cavity that is not completely lined
with mesoderm
Phyla Lophophorate
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includes the Bryozoa, Phoronida, and Brachiopoda.
named after a common structure, the lophophore.
 lophophore circular fold of the body wall bearing
ciliated tentacles that surround the mouth.
 The cilia draw water toward the mouth of these
suspension-feeders.
Cont…
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Bryozoans colonial animals
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Phoronids tube-dwelling marine worms ranging
from 1 mm to 50 cm in length.
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resemble mosses.
hard exoskeleton
the lophophore extend through pores in the
exoskeleton.
Almost all the 5,000 species of bryozoans are marine.
extend the lophophore from the tube when feeding and
pull it back in when threatened,
15 species of phoronids
Brachiopods, resemble clams and other bivalve
mollusks.
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All of the 330 extant species of brachiopods are marine,
30,000 species of these brachiopods in the fossil record
Phylum Nemertea
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proboscis worms or ribbon worms
bodies much like that of flatworms.
length from less than 1 mm to more than 30 m
900 species are marine, but a few species inhabit fresh
water or damp soil,
some are active swimmers, others burrow into the sand.
nemerteans have a complete digestive tract and a
closed circulatory system
Phylum Mollusca
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150,000 known species of diverse forms
snails and slugs, oysters and clams, and
octopuses and squids
Most mollusks are marine, though some inhabit
fresh water, and
some snails and slugs live on land,
mollusks are soft-bodied animals, but many are
protected by a hard shell of calcium carbonate
Foot, Visceral mass, Mantle
Radula
General Body Plan
8 classes of Mollusca Only 4
Prominent
Phylum Annelida
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Have segmented bodies.
15,000 species
length from less than 1 mm to 3 m
Annelids live in the sea, most freshwater
habitats, and damp soil.
digestive system consists of a pharynx, an
esophagus, crop, gizzard, and intestine.
Closed circulatory system
Metanephridia
brainlike pair of cerebral ganglia
cross-fertilizing hermaphrodites
Cont…
Poly-Hir.
Ecdysozoa
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Ecdysis
Phylum Nematoda and Phylum Arthropoda.
1. Phylum Nematoda- nonsegmented pseudocoelomates
covered by tough cuticles
Roundworms are found in most aquatic habitats
90,000 described species 1 mm to more than a meter
sheds its old cuticle and secretes a new, larger one
have a complete digestive tract and use the fluid in their
pseudocoelom to transport nutrients since they lack a
circulatory system
engage in sexual reproduction.
 play a major role in decomposition and nutrient recycling.
 The soil nematode, C. elegans, has become a model
organism in developmental biology
Nematoda Cont…
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Over 50 nematode
species, including
various pinworms and
hookworms, parasitize
humans
 Trichinella spiralis
 Heartworms
Arthropods
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segmented coelomates
exoskeletons and jointed appendages
estimated at a billion billion (1018) individuals
2 out of every 3 organisms known are
arthropods.
Arthropods must be regarded as the most
successful animal phylum
3 features: body segmentation, a hard
exoskeleton, and jointed appendages.
Arthropods Cont…
Arthropods Cont…
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exoskeleton made of layers of protein and chitin.
molt (ecdysis)
have well-developed sense organs, including eyes for
vision, olfactory receptors for smell, and antennae for
touch and smell
Arthropods have an open circulatory system
 hemolymph fluid is propelled by a heart through
short arteries into sinuses (the hemocoel).
Variety of specialized organs for gas exchange.
 Gills – Book Lungs – Trachea
trilobites (all extinct) chelicerates (horseshoe crabs,
scorpions, ticks, spiders) uniramians (centipedes,
millipedes, and insects) crustaceans (crabs, lobsters,
shrimps, barnacles, and many others)
Major Classes
Phylum Trilobita
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disappeared in the Permian extinctions about
250 million years ago
Chelicerates
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cephalothorax and a posterior abdomen.
chelicerae (pincers or fangs).
Most marine chelicerates are extinct four marine
species, including the horseshoe crab, survive today
modern chelicerates
are terrestrial and
belong to the
class Arachnida.
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Arachnids
scorpions, spiders, ticks, and mites
 six pairs of appendages.four pairs of walking legs
 pair of pedipalps function in sensing or feeding
chelicerae usually function in feeding
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Spiders inject poison from glands on the chelicerae
Spiders Book Lungs
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gas exchange is carried out by book lungs.
extensive
surface area,
enhancing
exchange of
gases between
the hemolymph and air
Uniramians
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Millipedes (class Diplopoda) 2 pairs of walking legs
 eat decaying leaves and plant matter
Centipedes (class Chilopoda) are terrestrial
carnivores.
 Centipedes have poison claws
 1 pair of walking legs.
Class Insecta
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outnumber all other forms of life combined
live in almost every terrestrial habitat and in
fresh water, and flying insects fill the air
26 orders
date back to the Devonian period, 400 million
years ago.
flight evolved in Carboniferous and Permian
periods
What came 1st pollinating insects or flowers???
Flight is one key to the great success of insects
Flight—The Insects Triumph
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escape many predators, find food and mates,
and disperse to new habitats.
Wings are extensions of the cuticle and are not
true appendages. So HOW DID THEY
EVOLVE???
 Absorb heat, glide, gills, swimming
 For sure did something before flight!!!
Crustaceans
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40,000 species of crustaceans most marine and
freshwater environments
lobsters, crabs, crayfish, shrimp, and
barnacles,
multiple appendages extensively specialized.
 crayfish have 19 pairs of appendages,
adapted to a variety of tasks.
separate sexes
Isopods, with about 10,000 species, are one of
the largest groups of crustaceans.
 Most are small marine species.
 They also include the land-dwelling pill bugs
Cont…
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Copepods (Krill)
Decapods, including
lobsters, crayfish, crabs,
and shrimp, are among the
largest crustaceans.
Metamorphosis
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Incomplete metamorphosis
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Complete metamorphosis.
Insect Impact
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Insects are important natural and agricultural
pollinators.
carriers for many diseases, including malaria
and African sleeping sickness.
Insects compete with humans for food
Food for many organisms
 Billions of dollars each year are spent by
farmers on pesticides to minimize their
losses to insects.
Deuterostomia
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Made of 2 phyla: Echinodermata and Chordata
we belong to chordata.
share the deuterostome characteristics of radial
cleavage, development of the coelom from the
archenteron, and the formation of the anus from
the blastopore.
These developmental features that define the
Deuterostomia are supported by molecular
evidence- DNA
Phylum Echinodermata
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Sea stars
 sessile, or slow-moving animals.
 water vascular system, a network of
hydraulic canals branching into extensions
called tube feet.
 These function in locomotion, feeding, and
gas exchange.
Reproduce sexually
All 7,000 or so species of echinoderms are
marine