aquatic chordates

chordate characteristics

• present in all chordates at an embryonic or adult stage

  • notochord

  • dorsal nerve cord

  • pharyngeal gill slits

  • post-anal tail

chordate subphyla

• urochordata

• cephalochordata

• vertebrata

urochordata

• tunicates & sea squirts

• marine

• solitary or colonial forms

• most adults sessile

cephalochordata

• genus Branchiostoma (formerly amphioxus)

• common name: lancelet

• costal areas

• burrow in sandy substrates, filter-feeders

vertebrata

• largest and most diverse subphylum

• shares 4 basic chordate traits with tunicates and lancelets

• novel traits:

  • cranium

  • vertebral column

  • jaws (for the most part)

  • endoskeleton

key innovations in vertebrate evolution

• jaws evolved from anterior gills arches of ancient jawless fishes

• teeth evolved from modified scales on the skin

• muscular gut and jaws facilitated predatory lifestyles

• closed circulatory system with heart and oxygen transport proteins enable high metabolic rates

• paired limbs for locomotion

five major groups of fishes

• myxiniformes

• petromyzontiformes

• chondrichthyes

• actinopterygii

• sarcopterygii

gnathostomata

• characteristics

  • upper and lower jaws evolved from anterior gill arches of jawless fishes

  • paired fins

sarcopterygii

• coelocanths, lungfishes, and tetrapods

• characteristics

  • single bone at base of paired fin/limb that articulates with the rest of the body

acinopterygii

• ray-finned fishes

• characteristics

  • fins composed of several long flexible rays connected with webbing

  • ~30,500 species

types of scales

• ganoid

  • nonteleost bony fishes

• placoid

  • cartilaginous fishes

• cycloid

  • teleosts

• ctenoid

  • teleosts

external anatomy

• morphology can affect feeding and type of habitat fish occupy

  • fish with small, upturned mouths generally are herbivores and/or surface feeders like silversides, mosquitofish, and topminnows

  • fish with down-turned mouths are generally bottom feeders loke hogsuckers

what body shape tells us

• fish like walleye, with a body long and tapered towards the ends (fusiform), are the best swimmers and need open water

• fish that are wide and flat tend to stay on the bottom (stencat madtom)

• fish that are rounded and thin from side to side, laterally compressed (compressiformed) tend to hover in the water and are not particularly fast swimmers (sunfish)

amphibia

• first terrestrial verts

• frogs, salamanders, newts

• “two lives'“- transitions from aquatic to land

  • lose post anal tail & gill slits

• requires moist environments

  • at least for reproduction & early development

• external fertilization

• three chambered heart

reptilia

• turtles, lizards, snakes, alligators, crocodiles

• evolved from amphibious ancestor- broke dependency to aquatic environment

• tough, scaly skin

  • prevents desiccation

• first sign of amniotic egg

  • key for transition to land

  • keeps embryo moist

• internal fertilization

aves

• descendants of reptiles

• adapted for flight

  • feathers

  • wings

  • light bones

  • flight muscles/ breastbone

• four-chambered heart

• extensive respiratory system

mammalia

• more efficient control over their body temperatures than even birds

• hair provides insulation

• mammary glands provide milk to nourish the young

• teeth are specialized for cutting, shearing or grinding; thick enamel helps prevent teeth from wearing out