phylum Chordata • around AT LEAST since Cambrian – 2 cm long, no appendages or eyes

• for 200 my restricted to ocean, ~360 mya evolved appendages, moved to land

• ~60,000 (?) extant species– 5500 spp. mammals (and 1/5th of those = bats)

• although numbers not impressive, size is:– land = 90,000 lbs, ocean = 220,000 lbs

phylum Chordata• subphylum Urochordata - sea squirts, tunicates• subphylum Cephalochordata - lancets, amphioxus• subphylum Craniata– class Myxini - hagfish– class Cephalaspidomorphi - lamprey– class Chodrichthyes - sharks, rays, mantas– class Osteichthyes - bony fish– class Amphibia - amphibians– class Reptilia - lizards, turtles, snakes– class Aves - birds– class Mammalia (Prototheria, Theria, Eutheria)

Gnathostomes

Vertebrates

debated… so going to follow

your frosh textbook…

• notochord – present in all embryos, not all adults– flexible rod, between digestive tube and (maybe) nerve cord

- support, purpose = muscle attachment

• dorsal hollow nerve cord– develops from ectoderm– in some develops into central nervous sys.

• pharyngeal gill slits or pouches– embryos develop pouches, which develop into slits in some

(humans becomes ear, thymus, etc.)

• post-anal tail– chordate tail extends past anus– all embryos have, lost in many adults (locomotion)

What makes a chordate?

hemichordates

• closest chordate outgroup– deuterostome, no wat vasc sys

• studies focus on development– embryogenesis homologs

• <200 spp.• Camb-Carbon fossils– extinct graptolites (sawblades)

subphylum Urochordata

• tunicates (“tunic”), sea squirts– ~3000 spp., all marine, filter feeders– solitary or colonial

• have all 4 as larvae– adults retain only gill slits

• larval stage = dispersal – short (few minutes?)

• adult stage = sessile

subphylum Cephalochordata

• lancelets, amphioxus– ‘both pointed’

• brain but no head• have all 4 as larvae AND adults• ~25 marine spp, fish like, reduced

nervous system• locally common, food resource– naturally Jamaica (Discovery Bay),

Asia commercial harvest

subphylum Craniata

• chordates with a head– have all 4 as larvae and adults, 9 classes– hagfish, lampreys & 7 classes of gnathostomes

e.g., BF1 and Otx cause swelling of dorsal nerve cord tip in lancelets

same genes regulate fore, mid, and hind brain in craniates

class Myxini • hagfish, agnathans, slime eel– ~30 spp., all marine

• cold oceans, both hemispheres• skull of cartilage, no jaws or

vertebrae• dead/dying fish, mostly annelids• slow metabolism – months w/o

eating• most ~1’ long, some 2-3’• spontaneously change sex

class Cephalaspidomorphi• lamprey, have vertebrae of cartilage– some highly reduced

• blood suckers– mouth best way to tell apart

• ~30 spp., marine and freshwater– cold water only

amphioxus:• notocord• epidermis• myomeres• digestive• reproductive?

lamprey external:• eyes• buccal funnel/mouth/teeth• nostril• gills• fins• cloaca

lamprey internal:• heart and ostia• brain• pineal gland• liver• olfactory sac• cranial cartilage • eye• notocord• nervous tissue• myomeres• ovary• intestine• gills• kidney? (up by liver)