40-1 copyright 2010 mcgraw-hill australia pty ltd powerpoint slides to accompany biology: an...

40-1Copyright 2010 McGraw-Hill Australia Pty Ltd PowerPoint slides to accompany Biology: An Australian focus 4e by Knox, Ladiges, Evans and SaintSlides prepared by Karen Burke da Silva, Flinders University

Chapter 40: Echinoderms and chordates


Deuterostomes• During embryonic development, the blastopore

becomes the anus• Phylum Echinodermata

– sea stars, sea cucumbers, sea urchins

• Phylum Chordata– acorn worms, sea squirts, lancelets, vertebrates


Fig. 40.1: Deuterostome phylogeny


Echinoderms• Sea stars, sea cucumbers, sea urchins, sea lilies,

brittle stars• Pentameric symmetry in adults• Characteristics

– calcareous endoskeleton– bilaterally symmetrical larvae– water vascular system


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)


Echinoderm 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


The 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


Fig. 40.3: Structure of a sea star


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)


Classification• Subphylum Hemichordata (acorn worms,

pterobranchs)

• Subphylum Urochordata (sea squirts, tunicates)

• Subphylum Cephalochordata (lancelets)

• Subphylum Craniata (fish, amphibians, reptiles, birds, mammals)


Chordate 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

Fig. 40.9: Chordate features



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)

Fig. 40.8: Acorn worm



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

Fig. 40.10a, b: Tunicates



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


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


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


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


Fig. 40.13: Evolution of jaws


Cartilaginous fishes: Chondrichthyes• Sharks, rays, skates, chimaeras• Characteristics

– skeleton of cartilage (frequently calcified)– fins with broad bases– no swim bladder– denticles in skin and along jaws

• Marine or freshwater (few species), benthic or pelagic


Ray-finned fishes: Actinopterygii• Sturgeons, paddlefish, barramundi, eels,

seahorses, butterflyfish etc.• Characteristics

– skeleton of bone– fins with narrow bases, supported by bony rays – swim bladder present– jaw formed of teeth-bearing dermal bone

• Marine or freshwater, benthic or pelagic

Fig. 40.16a: Structure of a bony ray-finned fish



Tetrapods and their relatives: 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

Fig. 40.17: Comparison between lobe-finned fish and tetrapod


Question 1:

The hagfishes and the lampreys:a) are a sister group of the sharks because they have

cartilaginous skeletons

b) have a rasping tongue homologous with the radula found in most molluscs

c) have retained paired pectoral and pelvic fins

d) are closely related parasites that bore into the sides of their hosts and then quickly secrete large quantities of mucous

e) are probably not any more related to each other than they are to the other fishes but are grouped together because they both lack jaws



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


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


Fig. 40.20: Relationships of amniotes


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– anapsid skull (lacks openings to accommodate jaw

muscles)– jaws toothless


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


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


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)

Fig. 40.29: Mammalian relationships



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


Fig. 40.31: Phylogeny of primates

Question 2:

Extinctions of animal species:a) are sufficiently rare that most animal species that have

evolved are still present on the earth today

b) always occur every 5 million years

c) only occur as a result of major global events, such as asteroid impacts or climate changes

d) have occurred at a relatively constant ‘background’ rate during periods when global environmental conditions have been relatively stable

e) do not occur as a result of competition or predation



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


Paranthropus: robust forms• 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)


Homo: increase in brain size• Oldest fossils of Homo are about 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 in Homo– 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


Out of Africa or a multiregional 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 semi-

independently from H. erectus–like ancestors simultaneously in different regions

Fig. 40.34: Suggested phylogeny of hominids


Summary• Echinoderms, hemichordates and chordates are all

deuterostomes• Echinoderms are radially symmetrical as adults• Chordates are characterised by a dorsal notochord

and pharyngeal slits • All tetrapods other than amphibians are amniotes• Amniotes evolved into two major groups: the

sauropsids and the mammals


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