Chordates, Vertebrates

Phylum 9: Chordates

  • mammals

  • birds

  • fish

  • humans

They have…

  • tube like digestive system

  • complex organs

  • have a coelom

  • bilateral symmetry

  • deuterostomes

Can be split into 3 phyla

  1. lancelets

  2. tunicates

  3. vertebrates

Chordates all have similar embryos, when they become adults, they can look very different.

How are they similar?

  1. all chordate embryos have a nerve cord that is both dorsal and hollow

    • vertebrates call this nerve cord the spinal cord and brain

  2. all chordate embryos have a notochord that acts as a flexible support rod

    • for vertebrates, the notochord has become reduced in adults. all that is left is pads that are cushioning between the backbone that became part of the discs of cartilage that cushion between the vertebrae

  3. pharynx in throat has supporting arches that have clefts that become open slits. water can enter the mouth, take a right turn and leave the digestive system through holes in the throat (gill slits in fish)

    • in reptiles and mammals, the pharyngeal clefts only made during the embryo stage

  4. all chordates have a muscular tail called post anal tail

Lancelets

  • thin animals, couple centimeters long

  • look like flat fish without any fins or eyes

  • okay swimmers, mostly in the sand with their head sticking up

  • found in shallow marine environments

  • filter feed with gills that have openings to the digestive system

Muscles are working off of the notochord, which allows them to do a controlled back and forth (like the tail moving on a fish)

Tunicates

  • small animals that vary a lot in their looks

  • typically (as adults) sessile

    • another filter feeder that feed with gill slits

    • after food is captured, water exits out of excurrent siphon

  • sessile ones are known as sea squirts

  • other tunicates can float (ex: salps)

Vertebrates

8 clades

  1. cyclostomes

    • jawless fishes

  2. chondrichthyes

    • cartilaginous fishes (ex: sharks)

  3. actinopterygii

    • ray finned fishes

  4. coelacanth

  5. lung fish

3,4 and 5 are collectively called the bony fishes

  1. amphibians

  2. reptiles

  3. mammals

Vertebrates are smarter than lancelets and tunicates

  • more complex brain

  • have an endoskeleton including a skull

  • have a backbone of vertebrae

  • skeleton can be made of bone and/or cartilage (softer flexible tissue)

  • closed circulatory system with high blood pressure that is powered by a ventral heart

Fish heart

  • usually only has 2 chambers inside

  • upper chamber that receives blood from rest of the body

  • pushes blood through valve into lower chamber that contracts and sends blood back to the body

Cyclostomes

  • lot have gone extinct, only 2 kinds left

  • lampreys and hagfish

  • no jaws so mouth cannot hinge closed (stuck in circular shape)

  • only have rudimentary vertebrae

  • missing paired fins

  • appeared around 500 million years ago

    • ostracoderms were early jawless fish that lived in salt water, but they now live in fresh water too

    • covered in bony armor, so they stayed on the bottom

    • descendants include lamprey and hagfish

      • lampreys look like eels

      • mostly in freshwater

      • most are parasites on other fish and sucks out some blood

      • hagfish are ugly and slimy

      • they are scavengers, go after soft bodied animals, get inside dead fish

      • can produce mucus that expands in contact with water

        • if predator tries to latch on, they slide off