ls6 bl4106 chordata i fish lancelet & seasquirts 2013
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Interesting lectureTRANSCRIPT
Phylum Chordata (I)
Lecture Series 6
Learning Outcomes • Outline the five distinctive hallmarks about chordates • Identify representatives from the following taxonomic
groups: – Subphylum Cephalochordates – Subphylum Urochordates – Subphylum Craniates
• Superclass Agnatha • Superclass Gnathostomata
– Class Chondrichthyes – Class Actinopterygii – Class Sarcopterygii
• Describe feeding and locomotion mechanisms in the taxonomic groups stated
Fig. 34-2
Lobed fins
Legs
Amniotic egg
Milk
Jaws, mineralized skeleton
Lungs or lung derivatives
Vertebral column
Head
Notochord
Common ancestor of chordates
ANCESTRAL DEUTERO- STOME
Echinodermata (sister group to chordates)
Chondrichthyes (sharks, rays, chimaeras)
Cephalochordata (lancelets)
Urochordata (tunicates)
Myxini (hagfishes)
Petromyzontida (lampreys)
Mammalia (mammals)
Actinopterygii (ray-finned fishes)
Actinistia (coelacanths)
Amphibia (frogs, salamanders)
Dipnoi (lungfishes)
Reptilia (turtles, snakes, crocodiles, birds)
Chordates Evolution (6:58’): http://www.youtube.com/watch?v=ypYesuV3PoI
Derived Characters of Chordates • All chordates share a set of derived
characters • Some species have some of these traits
only during embryonic development • Five key characters of chordates:
1. Notochord 2. Dorsal, hollow nerve cord 3. Pharyngeal slits or clefts 4. Endostyle or Thyroid Gland 5. Muscular, post-anal tail
Fig. 34-3
Dorsal, hollow
nerve cord
Anus Muscular,
post-anal tail
Pharyngeal slits or clefts
Notochord
Mouth
Muscle segments
Endostyle
5 Chordate Hallmarks 1. Notochord • The notochord is a longitudinal, flexible rod
between the digestive tube and nerve cord • It provides skeletal support throughout most of the
length of a chordate • In most vertebrates, a more complex, jointed
skeleton develops, and the adult retains only remnants of the embryonic notochord
2. Dorsal tubular nerve cord • The nerve cord of a chordate embryo
develops from a plate of ectoderm that rolls into a tube dorsal to the notochord
• The nerve cord develops into the central nervous system: the brain and the spinal cord
3. Pharyngeal pouches and slits • Functions of pharyngeal slits:
– Suspension-feeding structures in many invertebrate chordates
– Gas exchange in vertebrates (except vertebrates with limbs, the tetrapods)
– Develop into parts of the ear, head, and neck in tetrapods
4. Endostyle or Thyroid Gland • Functions of endostyle:
– Secretes mucus that traps small food particles brought into the pharyngeal cavity
– Endostyle is present in protochordates and lamprey larvae
– Some cells in the endostyle secrete iodinated proteins. – The cells are homologous with thyroid gland of adult
lamprey and the remainder of vertebrates – In ancestral chordates, an endostyle and perforated
pharynx act as an efficient filter-feeding apparatus
5. Postanal tail • Chordates have a tail posterior to the anus • In many species, the tail is greatly reduced
during embryonic development • The tail contains skeletal elements and
muscles • It provides propelling force in many aquatic
species
Lancelets • Lancelets (Cephalochordata) are
named for their bladelike shape • They are marine suspension feeders
that retain characteristics of the chordate body plan as adults
• Water enters mouth and passes through numerous pharyngeal gill slits
• Bears all 4 hallmarks of chordata
Fig. 34-4
Dorsal, hollow nerve cord
Notochord
Tail
Cirri
Mouth
Pharyngeal slits
Digestive tract
Atrium
Atriopore
Segmental muscles
Anus
2 cm
Urochordata (tunicates)
• 3000 spp • Marine • Most sessile but some free-swimming • They possess a tough non living tunic, test
that surrounds animal • Only larval form shows all hallmarks of
chordata • Adult form does not have notocord, tail
and dorsal nerve cord reduced to single ganglion
• Tunicates (Urochordata) are more closely related to other chordates than are lancelets
• They are marine suspension feeders commonly called sea squirts
• As an adult, a tunicate draws in water through an incurrent siphon, filtering food particles
• Predatory tunicates (0:23’): http://www.youtube.com/watch?v=e8jM94pNssc
Metamorphosis of sea squirt
Adult Tunicates or Sea Squirts
Sea Squirts (0:14’): http://www.youtube.com/watch?v=s95rfGnclX0
Craniates are chordates that have a head
• The origin of a head provided a new way of feeding for chordates: active predation
• Craniates share some characteristics: a skull, brain, eyes, and other sensory organs
• In aquatic craniates the pharyngeal clefts evolved into gill slits
Vertebrates are craniates that have a backbone
• During the Cambrian period, a lineage of craniates evolved into vertebrates
• Vertebrates became more efficient at capturing food and avoiding being eaten
Overview of Vertebrate Diversity Subphylum Vertebrata
Superclass Agnatha Superclass Gnathostomata Class Chondrichythes (cartilaginous fishes) Class Actinopterygii (ray-finned fishes) Class Sarcopterygii (lobe-finned fishes)
Class Amphibia Class Reptilia Class Aves Class Mammalia
1. Fish
2. Tetrapods
Jawless Fish Lampreys Hagfish
–Superclass Agnatha • Class Myxini (hagfishes) • Class Petromyzontida (lampreys)
–Superclass Gnathostomata • Class Chondrichythes (cartilaginous fishes)
–Subclass Elasmobranchii (sharks and rays) –Subclass Holocephali (chimeras)
• Class Actinopterygii (ray-finned fishes) –Subclass Chondrostei (chondrostean ray-
finned fishes) –Subclass Neopterygii (modern bony fishes)
• Class Sarcopterygii (lobe-finned fishes)
Superclass: Agnatha (Jawless fishes)
• Lack jaws • No paired fins • Taxonomy
– Class Myxini (hagfishes) – Class Petromyzontida (lampreys)
Myxini (Hagfishes) • Lack jaws & lack vertebrae • Only 43 marine species • Detritivore • Once dead body is found, it latches via
toothed plates and uses its tongue to rasp off bits of tissue
• For more leverage, it will tie a knot in their tail then slowly bring it forward so that it presses against the side of prey
• Hagfish predatory & slime defence (3:30’): http://www.youtube.com/watch?v=F8aVgSIDJjM
• Mucus Man (2:08’): http://www.youtube.com/watch?v=zdGGZJTmqEU
Lampreys
• Oldest living lineage of vertebrates but still lack jaws
• Marine or freshwater • Parasitic and non-parasitic forms
– Non-parasitic forms do not feed and die after spawning
– Parasitic forms attach to fish with sucker-like mouth, rasp off flesh with teeth and suck blood
• Fish attacked by lampreys
"Silent Invaders" Sea Lamprey 2013 (2:58’): http://www.youtube.com/watch?v=9JQ6oHjpeqU
Superclass Gnathostomata
• Jaws present • Paired limbs • Taxonomy:
– Class Chondrichythes (cartilaginous fishes) – Class Actinopterygii (ray-finned fishes) – Class Sarcopterygii (lobe-finned fishes)
• Today, jawed vertebrates, or gnathostomes, outnumber jawless vertebrates
Fig. 34-13-3
Skeletal rods
Cranium Gill slits
Mouth
Jaws evolved from the skeletal rods of the anterior pharyngeal slits. The remaining gill slits maintained their function in gas exchange.
• Cartilaginous skeleton • Bone entirely absent • Taxonomy:
– Subclass Elasmobranchii (sharks and rays) – Subclass Holocephali (chimeras)
Class Chondrichthyes (sharks, rays chimera)
Different species of sharks
Subclass Elasmobrachii (sharks and rays)
• Sharks – Predaceous – 5-7 gill slits – Tracks prey using lateral line and well
developed olfactory organs – Sharks have heterocercal tail which provides
lift as they swim – Placoid scales on skin which are modified to
form rows of teeth at mouth
Lateral line in shark
Rows of teeth
A. heterocercal - B. protocercal - C. homocercal - D. diphycercal
Lion of the ocean
• Great White Ambush (2:31’): http://www.youtube.com/watch?v=AOwdkMTwp6w
• Planet Earth Shark Jump (1:06’): http://www.youtube.com/watch?v=n-t2ayKadD0
• Rays – Dorsalventrally flattened – Enlarged pectoral fins used for swimming – Spiracles on top where water enters – Mouth and gill slits on ventral side
Subclass Holocephali (chimeras)
• 30 species • Fossil chimeras
appeared 120-50 million years ago where they were more abundant
• Mixed diet of seaweed and other marine prey
Ray-Finned Fishes and Lobe-Fins
• The vast majority of vertebrates belong to a clade of gnathostomes called Osteichthyes
• Osteichthyes includes the bony fish and tetrapods
• Nearly all living osteichthyans have a bony endoskeleton
• Most fishes breathe by drawing water over gills protected by an operculum
• Fishes control their buoyancy with an air sac known as a swim bladder
Fig. 34-16
Intestine
Adipose fin (characteristic of trout)
Cut edge of operculum
Swim bladder Caudal
fin
Lateral line
Urinary bladder Pelvic
fin
Anus
Dorsal fin Spinal cord
Brain
Nostril
Gills
Kidney Heart
Liver
Gonad
Anal fin
Stomach
Ray-Finned Fishes
• Class Actinopterygii, the ray-finned fishes
• The fins, supported mainly by long, flexible rays, are modified for maneuvering, defense, and other functions
Butterfly fish
Fig. 34-17
(a) Yellowfin tuna (Thunnus albacares)
(b) Clownfish (Amphiprion ocellaris)
(c) Sea horse (Hippocampus ramulosus)
(d) Fine-spotted moray eel (Gymnothorax dovii)
Lobe-Fins
• The lobe-fins (Sarcopterygii) have muscular pelvic and pectoral fins
• Three lineages survive and include coelacanths, lungfishes, and tetrapods
Fig. 34-18
Moving to land…