Download 40-7 Water vascular system

Chapter 40: Echinoderms and
chordates
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Deuterostomes
•
•
During embryonic development, blastopore
becomes anus
Phylum Echinodermata
– sea stars, sea cucumbers, sea urchins
•
Phylum Chordata
– acorn worms, sea squirts, lancelets, vertebrates
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Fig. 40.1: Deuterostome phylogeny
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Echinoderms
•
•
•
Sea stars, sea cucumbers, sea urchins, sea lilies,
brittle stars
Pentameric symmetry in adults
Characteristics
– calcareous endoskeleton
– bilaterally symmetrical larvae
– water vascular system
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Classification
•
Class Crinoidea (sea lilies, feather stars)
• Class Asteroidea (sea stars)
• Class Concentricycloidea (sea daisies)
• Class Ophiuroidea (brittle stars)
• Class Echinoidea (sea urchins, heart urchins, sand
dollars)
•
Class Holothuroidea (sea cucumbers)
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Anatomy
•
Endoskeleton
– calcite (CaCO3) spicules or ossicles embedded in
integument
•
Larva
– free-swimming, bilaterally symmetrical
– pentameric symmetry develops at metamorphosis
•
Water vascular system
– coelomic canals
– gas exchange and locomotion
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Water vascular system
•
•
•
Water enters through sieve-like madreporite
Stone canal → ring canal → radial canals
Stone canal
– calcified tube, connects madreporite to ring canal
•
Ring canal
– runs around base of arms
•
Radial canals
– run along arms; tube feet and ampullae for locomotion
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Fig. 40.3: Structure of a sea star
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Chordates
•
Acorn worms, sea squirts, lancelets, vertebrates
• Bilateral symmetry
• Characteristics
– notochord
– pharyngeal slits
– dorsal hollow nerve cord
•
Oldest fossils from Cambrian (530 million years
ago)
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Classification
•
Subphylum Hemichordata (acorn worms,
pterobranchs)
•
•
•
Subphylum Urochordata (sea squirts, tunicates)
Subphylum Cephalochordata (lancelets)
Subphylum Craniata (fish, amphibians, reptiles, birds,
mammals)
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Anatomy
•
•
Characteristics of chordates are present at some
stage of the life cycle
Notochord
– dorsal rod between nerve cord and gut, attachment point
for blocks of muscles (myotomes)
•
Pharyngeal slits
– paired openings in pharynx, used for filter feeding in
some chordates
•
Dorsal nerve cord
– hollow nerve cord above notochord, expanded anteriorly
to form brain in some chordates
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Subphylum Hemichordata
•
Acorn worms, pterobranchs
• Characteristics
–
–
–
–
•
tripartite body: proboscis, collar, trunk
pharyngeal slits filter food particles from water
mouth in groove between proboscis and collar
dorsal nerve cord in collar
Marine, solitary (acorn worms) or colonial
(pterobranchs)
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Subphylum Urochordata
•
Sea squirts, tunicates, salps
• Characteristics
– notochord and dorsal nerve cord in pelagic forms (larvae
and adults)
– incurrent and excurrent siphon for water intake and
expulsion
– pharyngeal slits filter food particles from water
– adult body encased in tunic composed of tunicin (form of
cellulose)
•
Marine, solitary or colonial, sessile or pelagic
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Subphylum Cephalochordata
•
Lancelets
• Characteristics
–
–
–
–
–
•
notochord extends for full length of body
muscle blocks (myotomes) along body
pharyngeal slits filter food particles from water
oral hood with buccal cirri around mouth
dorsal and tail fins, paired metapleural folds
Marine, solitary, benthic
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Subphylum Craniata
•
Jawless fish and vertebrates
– oldest fossil craniates are lower Cambrian (530 million
years ago)
•
Characteristics
– head with cranium (skull) of cartilage or bone
– brain with cranial nerves
•
Marine, freshwater or terrestrial, solitary, mobile
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Agnatha
•
•
Lampreys and hagfish
Characteristics
– cartilaginous skeleton
– notochord persists in adults
– lack jaws
•
•
Extinct jawless fish were bottom-dwelling filter or
detritus feeders
Modern jawless fish are blood-feeding
ectoparasites or scavengers
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Gnathostomata
•
•
Vertebrates (fish, amphibians, birds, reptiles and
mammals)
Characteristics
– vertebrae replace notochord in adult
– projections from vertebrae protect nerve cord and aorta
– neural crest cells give rise to many structures in the head
and other parts of the body
– dentine and enamel often form teeth or denticles
•
Evolution of jaws from gill-arches allowed
vertebrates to exploit a range of diets
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Fig. 40.13: Evolution of jaws
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Chondrichthyes
•
Cartilaginous fish: sharks, rays, skates, chimaeras
• Characteristics
–
–
–
–
•
skeleton of cartilage (frequently calcified)
fins with broad bases
lack swim bladder
denticles in skin and along jaws
Marine or freshwater (few species), benthic or
pelagic
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Actinopterygii
•
•
Ray-finned fish: sturgeons, paddlefish,
barramundi, eels, seahorses, butterflyfish etc.
Characteristics
–
–
–
–
•
skeleton of bone
fins with narrow bases, supported bony rays
swim bladder present
jaw formed of teeth-bearing dermal bone
Marine or freshwater, benthic or pelagic
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Sarcopterygii
•
Lobe-finned fish: coelacanths and lungfish
• Characteristics
– fins with broad, fleshy bases
•
Sarcopterygians are the closest relatives of
tetrapods (amphibians, sauropsids and mammals)
– similarities in pelvic girdle, pectoral and pelvic
appendages, dermal bones and heart
•
Marine or freshwater, benthic or pelagic
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Amphibia
•
Frogs, toads, newts, salamanders, caecilians
• Characteristics
–
–
–
–
–
•
skull with occipital condyles that articulate with vertebrae
single sacral vertebra
glandular skin without epidermal structures
eggs lack shells
lungs and skin used in gas exchange
Freshwater and terrestrial
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Amniotes
•
•
Vertebrates (sauropsids, mammals)
Characteristics
– extra-embryonic amnion encloses embryo in fluid-filled
sac
– embryonic allantois (outgrowth of hindgut) is used for
excretion during development
– thick, waterproof skin with scales, hair or feathers
– intervertebral disc
– atlas and axis are first two cervical vertebrae
•
Amniotes include Sauropsida (birds, ‘reptiles’) and
Mammalia
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Fig. 40.19: Relationships of amniotes
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Sauropsida: Chelonia
•
Turtles, tortoises and terrapins
• Characteristics
– body protected by dorsal and ventral shields (carapace
and plastron respectively)
– shoulder (pectoral) girdle lies inside rib cage
– skull anapsid (lacks openings to accommodate jaw
muscles)
– jaws toothless
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Sauropsida: Lepidosauria
•
Snakes, lizards and tuatara
• Characteristics
– teeth fused to edges of jaws
– some species can shed tail at pre-formed fracture points
(autotomy)
– snakes can disarticulate jaws to accommodate large prey
•
Tuataras (Sphenodon) of New Zealand are ‘living
fossils’
– only surviving members of order Rhynchocephalia
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Sauropsida: Archosauria
•
Crocodiles, birds, dinosaurs
• Characteristics
– diapsid skull with additional preorbital opening
– moveable membrane over eye
– muscular gizzard
•
Most of the diagnostic characteristics of birds are
adaptations to flight
– birds are descendants of the dinosaur lineage
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Mammalia
•
Characteristics
– epidermal hair
– milk production from mammary glands
– left aortic arch carries systemic circulation
•
Subclass Prototheria
– Order Monotremata (egg-layers)
•
Subclass Theria
– Order Metatheria (marsupials)
– Order Eutheria (placentals)
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Primates
•
•
Lemurs, tarsiers, monkeys, apes (including
humans)
Characteristics include
– prehensile digits and opposable thumb
– bicuspid premolars, molars with three to five cusps
– binocular vision, large brain
•
Strepsirhini (lemurs, lorises, galagos, pottos)
– rhinarium (nose pad) with slit-like nostrils
•
Haplorhini (tarsiers, monkeys, apes)
– nose with rounded nostrils
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Fig. 40.30: Phylogeny of primates
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The first hominids
•
•
Characteristic bipedal gait of hominids frees hands
for grasping food, holding young, nest-building and
tool-making
Sahelanthropus tchadensis (7 to 6 million years
ago)
– Djurab Desert, Chad, Africa
– ape-like brain case, short face and ‘human’ teeth
•
Australopithecus (4.4 to 2.5 million years ago)
– Ethiopia to South Africa
– forward-jutting face, brow-ridge, ‘human’ hands and molar
teeth
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Paranthropus
•
•
Tool-making hominids coexisted with Homo in
Africa
Paranthropus (2.8 to 1.6 million years ago)
– skulls with sagittal crests
– powerful jaw with large premolars
– vegetarian, used digging tools (probably for collecting
tubers and other plant material)
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Homo: increase in brain size
•
Oldest fossils of Homo are c. 2.5 million years old
– H. rudolfensis and H. habilis coexisted with
Australopithecus in Africa
•
Differences between Homo and Australopithecus
– brain capacity of Homo larger than Australopithecus
– reduction in jaw and tooth size
– evidence of tool-making (H. habilis)
•
More modern species with larger brain capacity
– H. ergaster from Africa
– H. erectus from Java (‘Java Man’) and China (‘Peking
Man’) made more sophisticated tools than H. habilis
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Origin of Homo sapiens
•
Competing theories of origin of Homo sapiens
• Out-of-Africa theory
– migration of anatomically modern humans from Africa,
replacing all other populations of Homo
– mtDNA evidence suggests a common ancestor 170 000
years ago
•
Multiregional theory
– anatomically modern humans evolved semiindependently from H. erectus-like ancestors
simultaneously in different region
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