Download 3/12/2015 An Introduction to Vertebrates II – The Bilateria Chapter 33B:

3/12/2015
Chapter 33B:
An Introduction to Vertebrates II –
The Bilateria
1. Lophotrochozoa
2. Ecdysozoa
3. Deuterostomia
Invertebrates
Porifera
ANCESTRAL
PROTIST
Eumetazoa
Lophotrochozoa
Bilateria
Common
ancestor of
all animals
Cnidaria
Ecdysozoa
Deuterostomia
Characteristics of Bilaterians
Bilaterians have the following characteristics:
• body plans with bilateral symmetry
• triploblastic development – endoderm, ectoderm & mesoderm
• most have a coelom and 2 digestive openings – mouth & anus
The Bilaterians consist of 3 major clades:
LOPHOTROCHOZOA
ECDYSOZOA
DEUTEROSTOMIA
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1. Lophotrochozoa
Porifera
Cnidaria
Ecdysozoa
Bilateria
Lophotrochozoa
Deuterostomia
Overview of the Lophotrochozoa
The clade Lophotrochozoa is based largely on molecular (DNA)
data, however there are other features that members of this
group tend to share:
• some have a lophophore – a ring of ciliated tentacles surrounding
the mouth
• some have a trochophore larval stage – free swimming ciliated
larva
• includes the following groups of animals: flatworms, rotifers,
ectoprocts, brachiopods, molluscs & annelids…
The Flatworms (Phylum Platyhelminthes)
The flatworms have the following general characteristics:
• they are triploblastic acoelomates
• they have a proctostome – a single opening to a
gastrovascular cavity
• gas exchange occurs by diffusion at the body surface
• osmotic balance is maintained through protonephrida
(“pre-kidneys”)
Flatworms have no circulatory system, so their flat shape increases the
surface area for the exchange of gases and other materials.
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Maximizing
Surface
Area
MAKE CONNECTIONS: Maximizing Surface Area
Folding
Flattening
SA: 6 (3 cm  3 cm) = 54 cm2
V: 3 cm  3 cm  3 cm = 27 cm3
• nutrient & waste
exchange are
most efficient the
greater the
surface area
relative to the
volume of the
organism
Thylakoid
1 µm
Projections
SA: 2 (3 cm  1 cm) + 2 (9 cm  1 cm)
+ 2 (3 cm  9 cm) = 78 cm2
V: 1 cm  3 cm  9 cm = 27 cm3
Diagrams comparing surface area (SA) for two
different shapes with the same volume (V)
Branching
• increased through
flattening & folding
Planarians
The main lineage of flatworms is the Rhabditophorans which
includes the planarians, flukes and tapeworms.
• planarians live in fresh water &
prey on smaller animals
Pharynx
Gastrovascular
cavity
Mouth
Eyespots
Ventral nerve cords
Ganglia
• planarians have light sensitive
eyespots and centralized nerve
nets more complex than the
cnidarians
• They are hermaphrodites that
can reproduce sexually or
asexually through fission
(splitting in two and regrowing
the missing half)
Trematodes (Flukes)
Human
host
All flukes are parasites with
complex life cycles involving
multiple hosts.
• flukes parasitic to humans
(e.g., liver flukes, lung flukes &
blood flukes) have life cycles
that involve snail species
Male
Female
1 mm
Blood Fluke
Life Cycle
Mature flukes
Motile
larva
Ciliated
larva
Snail host
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Cestodes (Tapeworms)
All tapeworms are also parasites with life cycles involving
multiple hosts.
100 µm
• absorb digested nutrients in the host’s intestine
• attach to the intestinal wall via hooks and suckers
on the scolex
• produce progressively mature
reproductive segments called
proglottids that detach from the
distal end full of eggs and pass out
with host feces
Hooks
Sucker
Proglottids with
reproductive
structures
Scolex
Rotifers
Rotifers (phylum Rotifera) tiny aquatic
animals smaller than many protists.
• have a pseudocoelom and
specialized organs
Crown
of cilia
around
mouth
Jaws
Anus
Stomach
0.1 mm
Lophophorates: Ectoprocts & Brachiopods
Lophophorates have
a true coelom and
ciliated tentacles
around the mouth.
Lophophore
Creeping bryozoan,
an ectoproct
•
ectoprocts are sessile
filter feeders with a
hard exoskeleton
•
brachiopods have a
hinged shell similar to
some molluscs and are
typically attached to
the sea floor
Lophophore
Lampshell, a brachiopod
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Molluscs
Metanephridium
The phylum
Mollusca includes
animals having a
general body plan
consisting of a
muscular foot,
visceral mass,
and mantle:
Visceral
mass
Heart
Coelom
Intestine
Digestive tract
Gonads
Mantle
Stomach
Mantle
cavity
Mouth
Shell
Radula
Anus
Gill
Foot
Nerve
cords
Esophagus
Mouth
Radula
…more on Molluscs
Molluscs also have the following features:
• most species have separate sexes though some such as the snails
are hermaphrodites
• many have ciliated trochophore larval stages
• most have a water-filled mantle cavity and feed with a radula
Molluscs are divided into 4 main classes:
POLYPLACOPHORA
BIVALVES
GASTROPODS
CEPHALOPODS
Polyplacophora (Chitons)
Chitons are marine animals armored with 8 dorsal plates.
• adhere to rocky
surfaces via a
muscular foot and
feed on algae
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Gastropods
Most gastropods (e.g., snails, slugs, abalone) have a single spiral
shell, are herbivores, and move slowly via a muscular foot.
• ~3/4 of all
molluscs are
gastropods
• most are
marine though
some live in
fresh water or
are terrestrial
(a) A land snail
(b) A sea slug (nudibranch)
Bivalves
Bivalves (e.g., clams, oysters, mussels, scallops) are filter feeders
with a shell divided into 2 hinged halves and a mantle cavity
Coelom
with gills used for gas exchange.
Hinge area
Mantle
Gut
Heart Adductor muscle
(one of two)
Digestive
gland
Anus
Mouth
Excurrent
siphon
Shell
Palp
Foot
Cephalopods
Mantle
cavity
Gonad
Gill
Water
flow
Incurrent
siphon
Squid
Cephalopods have beak-like
jaws surrounded by tentacles
derived from a modified foot.
Octopus
• includes species of
octopus, squid, cuttlefish
& nautilus
• have closed circulatory
system and complex nervous
system (considered the most
intelligent invertebrates)
Chambered
nautilus
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Annelids
Annelids are coelomates with segmented body composed of a
series of fused rings, that fall into 2 distinct clades – ERRANTIA
and SEDENTARIA:
Parapodia
• the ERRANTIA contain
pairs of parapodia on
each segment, each with
numerous chaetae –
bristles made of chitin
Sedentarians
Sedentarians tend to be less mobile than errantians, many of which
burrow into the surrounding substrate or live in protective tubes:
• tube-dwelling sedentarians typically have
elaborate gills or tentacles used for filter feeding
• this clade also
includes the
earthworms &
leeches
Earthworms
• earthworms are a good example of annelids,
having a closed circulatory system and a
complete digestive tract (mouth & anus)
Epidermis Cuticle Coelom
Circular muscle
Metanephridium
Dorsal
vessel
Chaetae
Metanephridium
Clitellum
Pharynx
Crop
Intestine
Cerebral
ganglia
Gizzard
Mouth
Intestine
Nephrostome
Skin
Esophagus
Septum (partition
between segments)
Longitudinal muscle
Anus
Ventral vessel
Fused
nerve cords
Subpharyngeal
ganglion
Ventral nerve cords
Circulatory system vessels
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2. Ecdysozoa
Porifera
Cnidaria
Lophotrochozoa
Ecdysozoa
Deuterostomia
Overview of the Ecdysozoa
The clade Ecdysozoa is the most diverse group of animals, most
of which are covered by a tough cuticle that is periodically
shed and replaced by molting.
The 2 largest phyla are the:
NEMATODA (roundworms)
ARTHROPODA
Nematodes
The Nematodes or roundworms have a complete digestive tract
but lack a circulatory system.
• some such as Trichinella are parasites that live and feed in animal tissues
Encysted juveniles
Muscle tissue
50 µm
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Arthropods
2/3 of all animal species are arthropods which have the
following general features.
Arthropoda (1,000,000 species)
• a segmented body with a
hard exoskeleton made of
chitin and protein that is
molted as it grows
• jointed appendages that
come in pairs
• open circulatory system
A scorpion (an arachnid)
Cephalothorax
Antennae
(sensory
reception)
Arthropod
Body Plan
Abdomen
Thorax
Head
Eye
Swimming appendages
(one pair per abdominal
segment)
Pincer
(defense)
Mouthparts
(feeding)
Walking legs
3 Major Lineages of Arthropod
CHELICERATES
• arachnids, horseshoe crabs
MYRIAPODS
• centipedes, millipedes
PANCRUSTACEANS
• insects, crustaceans
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Chelicerates
Most marine chelicerates are extinct with the exception of
the horseshoe crabs.
The vast majority of
living chelicerates are the
terrestrial arachnids…
Arachnids
50 µm
Arachnids include spiders, mites,
ticks & scorpions.
Scorpion
Arachnids have 6 pairs of
appendages, 4 of which are
walking legs. Heart
Dust mite
Web-building spider
Book lungs
Chelicera
Pedipalp
Myriapods
• millipedes have 2 pairs of
legs per segment and eat
decaying plant matter
(a) Millipede
• centipedes have
1 pair of legs per
segment and are
carnivorous
(b) Centipede
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Pancrustaceans
Insects
Remipedians
(a crustacean group)
Common ancestor
of arthropods
Other
crustaceans
Myriapods
Chelicerates
Crustaceans
• crustaceans are mostly
aquatic (crabs, shrimp,
barnacles, krill, etc)
• also includes the terrestrial
isopods (pill bugs)
Insects
The clade Hexapoda includes all insects and their relatives,
most of which are terrestrial.
• have complex organ
systems
• many are capable of flight
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Abdomen
Thorax
Anatomy of
an Insect
Head
Compound eye
Antennae
Heart
Dorsal
artery
Cerebral ganglion
Crop
Anus
Vagina
Malpighian
tubules
Ovary
Nerve cords
Tracheal tubes
•
Mouthparts
Metamorphosis
many insects
undergo complete
metamorphosis in
which the larval
and adult stages
are very different
(a) Larva
(caterpillar)
(b) Pupa
(c) Later stage
pupa
(d) Emerging
adult
(e) Adult
•
others undergo incomplete
metamorphosis in which the
larval and adult stages
resemble each other
3. Deuterostomes
Porifera
Cnidaria
Lophotrochozoa
Ecdysozoa
Deuterostomia
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Overview of the Deuterostomes
The clade Deuterostomia includes species with radial cleavage
and an anus derived from the blastopore and contains 2 major
lineages:
ECHINODERMATA
• sea stars, urchins, sand dollars, etc.
CHORDATA (to be addressed in chapter 34)
• all vertebrates and a few
invertebrate chordates
Echinoderm Features
Digestive tract
Stomach
Anus
Spine
Gills
Madreporite
Central disk
Radial
nerve
Digestive glands
Ring
canal
• adults have
radial symmetry
with multiples of
5 (larvae have
bilateral
symmetry)
Gonads
Ampulla
Podium
Tube feet
Radial canal
• have an
endoskeleton of
calcareous plates
Living echinoderms fall into one of 5 clades:
ASTEROIDIA – sea stars & sea daisies
OPHIUROIDIA – brittle stars
ECHINOIDIA – sea urchins & sand dollars
CRINOIDIA – sea lilies & feather stars
HOLOTHUROIDIA – sea cucumbers
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Asteroidia
Includes the sea stars
which have 5 arms and
prey on bivalves by prying
them open.
Also includes the sea
daisies which absorb
their nutrients.
Ophiuroidia – “Brittle Stars”
Brittle stars have a distinct central disc from which 5 slender
arms extend.
• some species are
predatory or
scavengers and
others are filter
feeders
Echinodea – “Sea Urchins & Sand Dollars”
Sea urchins and sand dollars lack arms but have 5 rows of tube
feet.
• urchins have spines for
protection and feed on
seaweeds
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Crinodea – “Sea Lilies & Feather Stars ”
Sea lilies are sessile while feather stars crawl using long flexible
arms.
Both are suspension
feeders.
Holothuroidea – “Sea Cucumbers”
Sea cucumbers lack spines, have a reduced endoskeleton and 5
rows of tube feet.
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