Transcript Animals File - Moodle

Lecture Topics
• What is an animal?
• Evolutionary trends in animals
• Introduction to some representative
animal phyla
What is an Animal?
• Animals are very diverse but do share some
general common characteristics
– Multicellular heterotrophic eukaryotes
– Ingest food
– Diploid
– Capable of locomotion
– Reproduce sexually, but asexual
reproduction is common
– Lack cell walls
• Appear to be a monophyletic group
Evolutionary trends
• Germ Layers – embryonic cell layers
– Begin with single undifferentiated layer
• E.g., Porifera
– Diploblastic – two germ layers:
• E.g., Cnidaria
• Ectoderm (outer) Skin & nerves
• Endoderm (inner) Gut
– Triploblastic – adds a third germ layer
– E.g., Arthropoda
• Mesoderm (middle) Muscle, many organs
Evolutionary trends
• Digestive tract
– Begins with no digestive tract
• E.g., Porifera
– Blind sac with food in and waste back out
• E.g., Cnidaria
– One way gut – tube within a tube
• E.g., Annelida
Triploblastic
Body Plans
• Acoelomates
– Solid body
construction
• Pseudocoelomates
– Lined on only
outer side with
mesoderm
– No mesentery
• Coelomates
– Completely
surrounded by
mesoderm
– Mesentery
suspends gut from
body wall
Evolutionary trends
• Body symmetry
– Asymmetry = None
• Porifera
– Radial symmetry = Symmetric
(mirror image) about oral-aboral axis
• Cnidaria (mostly?)
– Bilateral symmetry = Symmetric
only about one plane
• Pretty much everything else
Sections,
Directions,
and
Symmetry
Evolutionary trends
• Cephalization -- formation of a distinct
head
– Associated with Bilateral symmetry
– Puts sensory organs and mouth in the
lead
– Generally considered an adaptation for an
active lifestyle
– Contrast Porifera, Cnidaria,
Echinodermata with Annelida and
Arthropoda
Segmentation, Metamerism, and
Tagmatization or Tagmosis
• Segmentation – division of body into distinct
segments able to operate independently of
one another
• Metamerism – serial repetition of body parts
– Contrast Nematoda vs Annelida or Arthropoda
• Tagmatization – organization of segments
into functional units (e.g., head, thorax,
abdomen)
– Contrast Annelida vs. Arthropoda
Sponges: Phylum Porifera
• Germ Layers – None – Very loosely
organized – can sift cells and will
regenerate
• Digestive tract – None – Choanocytes filter
food from water, amebocytes transfer
nutrients
• Coelom – None
• Symmetry – None
• Segmentation – None
Unique Structures
• Spicules – Silica or calcium carbonate
• Spongin – Flexible protein
• Choanocytes – Collar cells – similar to
choanoflagellates
– Drive water flow in ostia and out osculum
Osculum
Epidermal
cell
Spongocoel
Incurrent
pores
Water movement
Porocyte
Spicule
Collar cell
Flagellum
Microvillus
Collar
Amoeboid cell
in mesohyl
Nucleus
Figure
28-6b
Page 542
Jellyfish, Anemones, Corals,
Hydra : Phylum Cnidaria or
Coelenterata
• Germ Layers – Two, with gelatinous
mesoglea between endoderm and ectoderm
• Digestive tract – Blind sac – food enters and
exits through mouth
• Coelom – None
• Symmetry – Radial
• Segmentation – None
Unique Structures
• Cnidocytes with Nematocycts – Stinging
cells with venomous harpoons
• Polyp – Sessile form e.g., Anemone, Hydra
• Medusa – Swimming form, e.g., Jellyfish
Two major clades of animals:
Protostomes vs. Deuterostomes
• Embryonic origin of gut
– Protostome = First Mouth – Mouth arises from
blastopore – first invagination of blastula (hollow
ball of embryonic cells)
– Deuterostome = Second mouth – Anus arises
from blastopore
• Early development
– Protostomes – Determinate, spiral cleavage,
coelom originates from solid mass of cells
– Deuterostomes– Indeterminate, radial cleavage,
coelom originates as pouches off gut
Fig. 32.3
Phylogeny undergoing revision
• Protostomes now divided into two clades
– Spiralia
– Ecdysozoa (animals that molt)
• Flatworms previously considered separate clade -Acoelomates
• Nematodes and rotifers previously considered
pseudocoelomates (not protostome coelomates) but
molecular evidence suggests protostome ancestry
(details change with new data)
• Now flatworms, nematodes, and rotifers considered
simplified coelomates
– Flatworms in Platyzoa within Spiralia
– Nematodes in Ecdysozoa
Segmented Worms:
Phylum Annelida
•
•
•
•
•
Germ Layers – Three
Digestive tract – One way gut
Coelom – True coelom
Symmetry – Bilateral
Segmentation – Yes, with metamerism
Snails, Bivalves, Cephalopods:
Phylum Mollusca
• Germ Layers – Three
• Digestive tract – One way gut
• Coelom – True coelom with mesentery –
lined with mesoderm on both inner (gut)
and outer (body wall) surfaces
• Symmetry – Bilateral
• Segmentation -- ? Chitons have serial
plates
Unique Structures
• Radula – Rasping structure on “tongue”
• Calcium carbonate shell (absent in slugs,
internal in most cephalopods) secreted by
mantle
Giant squid
Architeuthis dux
• World’s largest invertebrate (18m, 900kg)
Ecdysozoa
Protostomes that molt
• Arthropods – Rulers of the planet!
(insects, spiders, crustaceans, etc.)
Insects, Arachnids, Crustaceans,
Myriapods, etc.: Phylum Arthropoda
•
•
•
•
•
Germ Layers – Three
Digestive tract – One way
Coelom – True coelom
Symmetry – Bilateral
Segmentation – Yes, with tagmatization
(head, thorax and abdomen or
cephalothorax and abdomen or
head and trunk)
Unique Structures
• Jointed Appendages
• Chitinous exoskeleton (remember
chitin?…)
• Wings (insects)
• Chelae (crabs)
Photographer: Alan Gornick Jr.
©Aris Multimedia Entertainment, Inc. 1994
Deuterostomes
• Echinoderms
• Chordates
Phylum Echinodermata
•
•
•
•
•
Germ Layers: Three
Digestive tract: One way
Coelom
Symmetry: Bilateral (“pentaradial”)
Segmentation: In arms?
Unique Structures
• Water vascular system with tube feet
• Pedicellaria -- tiny pincers on flexible
stalks
• Dermal skeleton of calcium carbonate
Digestive
gland
Stomach
Gonad
Digestive
gland
Tube feet
Tube feet
Anus
Ampulla
Gonad
Spine
Dermal gill
Pedicellariae
Tube feet
5 mm
Figure 30-2
Page 577
Phylum Chordata
• Very successful
• Includes 3 subphyla, some invertebrate
– Urochordata – tunicates
– Cephalochordata – lancelets
– Vertebrata
Vertebrata
Cephalochordata
(lancelets)
Urochordata
(tunicates)
Hemichordata
(acorn worms)
Echinodermata
(sea stars,
sea urchins)
Chordata
2 out of 3
chordate
subphyla are
invertebrates
Cranium,
vertebral
column
Notochord,
dorsal tubular nerve cord,
pharyngeal slits,
postanal tail
Deuterostome
ancestor
Tadpole Larva
Cephalochordata
(lancelets)
Chordata
Deuterostome
ancestor
Figure 30-6
Page 581
Subphylum Cephalochordata:
The Lancelet or Amphioxus
Branchiostoma sp.
Tentacles
Nerve
cord
Notochord
Gill slits
Intestine
Caudal fin
Tentacles
Endostyle
Atrium
Gonads
Atriopore
Anus
Chordate
ancestor
Jaws
Vertebrae
Jawless fishes
Limbs
Lungs (for swim
bladder)
Mammalia
Aves
(birds)
Reptilia
Amphibia
Dipnoi
(lungfishes)
Actinistia
(coelacanths)
Actinopterygii
(ray-finned fishes)
Chondrichthyes
(cartilaginous fishes)
Cephalaspidomorphi
(lampreys)
Myxini
(hagfishes)
Cephalochordata
(lancelets)
Urochordata
(tunicates)
Craniates
V e r t e b r a t e s
Amniotes
Amniotic egg