The Phylum
Chordata
The Chordates
• Phylum Chordata
• Subphyla:
Urochordata,
Cephalochordata, &
Vertebrata
The Vertebrate Classes
• agnatha -jawless fish,
• chondrichthyes-cartilage fish,
• osteichtheyes- bony fish
• amphibia,
• reptilia,
• aves -birds,
• mammals
Characteristics shared by all chordates
at some stage in their lives:
• 1) notochord -stiff rod of specialized cells,
encased by a firm sheath along the length of the
dorsal side. It becomes the vertebrate
backbone
notochord development
in a zebra fish embryo
notochord in
a lancet
• 2) gill slits or pharyngeal pouches:
seen in embryos, develop into gills in fish
& other similar structures
• 3) dorsal hollow nerve cord : ( bundle of
nerves runs down the back) above the
notochord, the anterior end develops
into the brain, & the remaining part
becomes the spinal cord (part of the
Central Nervous System)
• 4) post anal tail - Extension of the body past
the anal opening - -amphioxus
propels aquatic forms
Phylum Hemichordata - Protochordates –
Lack some key chordate characteristics
• Body in three parts: proboscis, colar and
trunk
Enteropneusta – Acorn worms (solitary,
live in mud or vegetation)– filter feeders .
• Pterobranchia – (pterobranchs) – tiny
deep-sea colonial moss like animals –
No trace of a notochord.
• They live in secreted tubes.
• Larval stage – “Planktonic snails – Sea
Angels” The larva settle on substrate and
reproduce asexually by budding to create
a new colony.
Sub phylum Urochordata: “Sea
Squirts” (Tunicates)
• Larval Form = tunicate larva possess all four
characteristics
• Larvae are tadpole-like and free-living, and have an
endostyle, gill slits, dorsal nerve cord, and
notochord.
• The larval stage lasts only a few days, and ends
when the larva attaches to a substrate and
metamorphoses into an adult.
• Adult is sessile (and sometimes colonial), and
must obtain food by siphoning sea water through
its body and trapping food particles in the
endostyle.
• Their outer covering is called the tunic_ barrelshaped animals that live on the ocean bottom.
• Adapted
for
filter-feeding.
• They are hermaphrodites. Fertilization is
_external_. They have a pouch-like _pharynx_
but no notochord, nerve cord, or post anal tail.
Eat Them!
Subphylum - Cephalochordata:
Lancelets
• The Origin of the free-swimming vertebrates (Led to
Fish - actively feeding & predatory)
• Structures shows cephalzation.
1) blade-shaped animals they retain: notochord,
dorsal nerve cord, pharyngeal pouches, & post
anal tail, (They are weak swimmers, and burrow
into sand.)
2) Live in shallow warm water.
3) Use cilia to draw in water and trap food, water
leaves body through the atriopore.