urochordata - west virginia universitysraylman/comparative/lectures/2uro,ceph,craniata.pdf ·...
TRANSCRIPT
• Phylum Chordata
– Subphylum Urochordata (Tunicata)
– Subphylum Cephalochordata
– Subphylum Craniata
-Vertebrata • Superclass Agnatha
• Superclass Gnathostomata
– Class Placodermi
– Class Chondrichthyes
– Class Acanthodii
– Class Osteichthyes
– Class Amphibia
– Class Reptilia
– Class Mammalia
– Class Aves
Urochordata • Sessile filter feeder – cilia move water and food,
filtering in pharyngeal ‘pouch’ (pharynx)
Water + Food
In
Gets
filtered
Water
Out
• Endostyle – ciliated groove within pharynx
– secretes mucous for food capture
– metabolizes iodine - homologous to thyroid
Endostyle
Urochordata • Monoecious (hermaphroditic) - each
individual produces male and female gametes.
Gametes
released
Urochordata
• Adult lacks most chordate synapomorphies
Urochordata
Urochordata larvae
Eyespot and
statocyst
• Phylum Chordata
– Subphylum Urochordata (Tunicata)
– Subphylum Cephalochordata
– Subphylum Craniata
-Vertebrata • Superclass Agnatha
• Superclass Gnathostomata
– Class Placodermi
– Class Chondrichthyes
– Class Acanthodii
– Class Osteichthyes
– Class Amphibia
– Class Reptilia
– Class Mammalia
– Class Aves
Cephalochordata • Motile filterfeeders
– ciliated wheel organ and pharynx
– Notochord – “hydroskeleton”
– Stiffness of notochord under neural control
amphioxus
Notochord extends
into anterior end
Cephalochordata
• Amphioxus
• Tail musculature and associated nerves & vessels are segmented.
– ‘Metamerism” myomeres
Cephalochordata
• Amphioxus
• Circulatory system with dorsal and ventral aorta.
• Metapleural fold – stability for swimming
Cephalochordata
In text, Euchordates = Somitichordates
• Pikaia gracilens - 530 million years ago
– myomeres (muscle blocks)
– skeletal notochord
– cephalization
• Cambrian explosion - ~550 million y.a.
– Burgess shale
• Phylum Chordata
– Subphylum Urochordata (Tunicata)
– Subphylum Cephalochordata
– Subphylum Craniata
-Vertebrata • Superclass Agnatha
• Superclass Gnathostomata – Class Placodermi
– Class Chondrichthyes
– Class Acanthodii
– Class Osteichthyes
– Class Amphibia
– Class Reptilia
– Class Mammalia
– Class Aves
Craniata
• Chordates with skulls, neural crest
– cartilagenous, fibrous or bony
– encases brain & sense organs
contains hagfish and all vertebrates
Hagfish
Lamprey
Craniata • Sensory, digestive and respiratory anatomy
Neural crest cells • NC cells are found in all craniates and give
rise to a variety of structures
QuickTime™ and a Animation decompressor are needed to see this picture.
• It’s nice to have a neural crest…. – pigment cells
– gill arches, jaw
– ganglia in ANS
– base of skull
– induce skin ‘structures’
Craniata vs. ‘protochordates’
• Selection for predatory characteristics
– active feeders
– muscular gut tube for filtering
Evolutionary scenarios • Craniates were originally linked
w/arthropods, annelids, mollusks
– But essential differences in development
– Segmentation is different
Garstang (p.44)
• Euchordates (Somitochordates) evolved via paedomorphosis (a type of heterochrony)
• Paedomorphosis: Adult form of the descendant species retains juvenile features of ancestral species.
Linking the subphyla
Adult salamander
w/gills
• Garstang: Mutation caused development of sexual maturity in a non-metamorphosing lineage of Urochordata – better locomotion
• Early craniates – larger, more mobile than cephalochordata. Driven by predation?
• Conodonts - 540-230 m.y. ago
– after Pikaia, the next fossil Chordates
– microfossils of teeth, probably in pharynx
Cool thing about conodonts
• A new hard substance appears: mineralized tissue – calcium phosphate (hydroxyapatite)
Hagfish • Scavenge dead, dying fish and invertebrates. Have
funnel-like mouths - tongue rasps off food.
Vertebrates • Metameric skeletal elements flanking the nerve
cord.
• Neural arch was first element to evolve
Hagfish
Lamprey
Shark
• Phylum Chordata
– Subphylum Urochordata (Tunicata)
– Subphylum Cephalochordata
– Subphylum Craniata
-Vertebrata • Superclass Agnatha
• Superclass Gnathostomata – Class Placodermi
– Class Chondrichthyes
– Class Acanthodii
– Class Osteichthyes
– Class Amphibia
– Class Reptilia
– Class Mammalia
– Class Aves
• “Ostracoderms” – 430-370 million years ago - early jawless fish
– head shields w/mineralized bone
– small bottom-dwelling
• Calcium phosphate mineralized tissue makes head shield and is related to teeth and scales
– enamel and dentine
– developmental interaction of epidermis and dermis
Ancestral jawless fish
• Usually no paired fins
• Notochord mostly remains
• Single nostril
• Main groups of modern jawless fish:
– Hagfish (Myxiniformes)
– Lamprey (Petromyzontiformes)
Similarities in these two groups are probably due
to evolutionary convergence (homoplasy)
Lamprey respiration
• Water flows in mouth, through respiratory tube and out gills
• Respiratory tube internally connects gill pores
• Specialized flap - velum can close off anterior end of respiratory tube
!!
• Branchial muscles squeeze water in and out of respiratory tube and over gills
• “Tidal ventilation”
!!
• Ammocetes - larval form of lamprey
– up to 7 years
• Uses muscular movements to make feeding current.