Lecture #14 Phylum Chordata: The vertebrate Phylum

Phylum Chordata only 45,000 species characteristics: – 1. bilaterally symmetrical – 2. notochord – 3. pharyngeal gill slits – 4. dorsal, hollow nerve cord – 5. post-anal tail – 6. complete digestive system – 7. thyroid gland – 8. ventral, contractile heart Numbers 1 – 5 may be in a unique combination and are found at some stage in development

Chordate classification characteristics: Notochord? No  Echinoderms Notochord? Yes  keep evolving Brain? No  Urochordate (tunicate) Brain? Yes  keep evolving Head/Cranial cavity? No  Cephalochordate (lancelet) Cranial cavity? Yes  keep evolving Vertebral column? No  Hagfish Vertebral column? Yes  Lampreys & keep evolving baby!!! Chordates Echinodermata (sister group to chordates) Craniates Vertebral column Head Brain Notochord Ancestral deuterostome Cephalochordata (lancelets) Myxini (hagfishes) Cephalaspidomorphi (lampreys) Urochordata (tunicates)

Phylum Chordata notochord: – supportive rod that extends most of the animal’s length – extends into the tail – dorsal to the body cavity – flexible to allow for bending but resists compression – composed of large, fluid-filled cells encased in a fairly stiff fibrous tissue – will become the vertebral column in many chordates

Phylum Chordata dorsal, hollow nerve cord: – runs along the length of the body – dorsal to the notochord – expands anteriorly as the brain – develops from ectoderm – BUT: in most vertebrates – nerve cord is solid and is ventral to the vertebral column

Phylum Chordata pharyngeal gill slits: – series of openings in the pharyngeal region of the embryo – develop as a series of pouches separated by grooves – in some embryos – grooves develop into slits – used in primitive chordates for filter feeding – in aquatic vertebrates – transformed these slits/pouches into gills – embryonic in terrestrial chordates

Phylum Chordata SubPhyla: – Urochodata: sea squirts (tunicates) notochord, pharyngeal gill slits, and tail present in free- swimming larvae – Cephalochordata: amphioxus all four chordate traits persist through life – Hyperotreti: hagfishes jawless, no paired appendages – Vertebrata: vertebrates

Subphylum Cephalochordata known as the lancelets earliest diverging group of chordates get their name (Lancelet) from their blade-like shape embryos develop: a notochord, a dorsal, hollow nerve cord, pharyngeal gill slits and a post-anal tail filter-feeders – cilia draw water into the mouth swim like fishes – chevron shaped muscles on either side of the notochord Pharyngeal slits or clefts Mouth Brain Dorsal, hollow nerve cord Notochord Muscle segments Muscular, post-anal tail Anus

Subphylum Urochordata tunicates embryonic/larval stage has the characteristics of the chordate larva swims to a new substrate and undergoes metamorphosis – to form the adult tunicate retain the pharyngeal gill slits in the adults water flows in through an incurrent siphon - filtered by a net of mucus on the pharyngeal gill slits Incurrent siphon to mouth Excurrent siphon Pharynx with numerous slits Atrium Tunic Excurrent siphon Anus Intestine Esophagus Stomach

Craniates chordates with a head head – consists of a brain, surrounded by a skull, and other sensory organs living craniates all share a series of unique characteristics most basic craniate – hagfish AyU

Vertebrates branching off from the primitive chordates involved innovations in the nervous system and skeleton – vertebraes have a more extensive skull – development of the vertebral column composed of vertebrae most vertebrates – vertebrae enclose a spinal cord (replaces the notochord) – development of fin rays in aquatic vertebrates – development of limbs in terrestrial vertebrates adaptations in respiration and circulation – more efficient gas exchange system – gills are modified in aquatic vertebrates; lungs in the terrestrial vertebrates – more efficient heart – 2 to 4 chambered adaptations in thermal regulation – warm blooded vs. cold blooded adaptations in reproduction – amniotic egg – placental animals

Vertebrate Taxonomy most basal vertebrate – lamprey – jawless development of jaws marked the evolution of the gnathostomes development of ray-finned fishes development of lobed fins marked the evolution of lobe- finned fishes development of limbs marked the development of amphibians and reptiles development of mammary glands marked the development of mammals lungs marked the evolution

Vertebrate classification requirements: Vertebral column? No  Hagfish Jaws? No  Lampreys Bony skeleton? No  Sharks, Rays Lobed fins? No?  Ray finned fish Lung derivatives? No  Coelocanth Legs? No  Lungfish Amniotic egg? No  Amphibian Milk? No  Reptile What’s left??? MAMMALS!! Chordates Echinodermata (sister group to chordates) Craniates Vertebrates Gnathostomes Osteichthyans Lobe-fins Tetrapods Amniotes Milk Legs Amniotic egg Mineralized skeleton Jaws Vertebral column Head Brain Notochord Ancestral deuterostome Cephalochordata (lancelets) Myxini (hagfishes) Cephalaspidomorphi (lampreys) Chondrichthyes (sharks, rays, chimaeras) Actinopterygii (ray-finned fishes) Actinistia (coelacanthus) Dipnoi (lungfishes) Urochordata (tunicates) Amphibia (frogs, salamanders) Reptilia (turtles, snakes, crocodiles, birds) Mammalia (mammals) Lobed fins Lung derivatives