Tripart body (3 parts) - proboscis, collar and trunk
characters similar to chordates - dorsal nerve cord(deuterostomes) (not hollow) and ventral nerve cord as well (protostomes) and stomachord (endoderm, not homologous)
Homologous with chordates - pharyngeal slits, iodine sequestering in pharynx, some with post anal tail in juveniles
A) trunk
B) proboscis
C) mouth
D) collar
Enteropneusta (Acorn worm)
Benthic filter feeders using cilia to generate feeding current and mucus to trap food particles
Mucus generated dorsally in the pharynx food collects ventrally
Pterobranchia (feather ones)
colonial filter feeders with collar modified into ciliated tentacles
not in the phylum chordata because only a few of the chordate synapomorphies certain ----
pharyngeal slits
iodine sequestering cells
post anal tail
Chordates are upside down hemichordates
Chordate body plan
Chordate body plan... continued
at some point in their life all chordates have 4 basic characteristics (shared and derived)
dorsal nerve chord (hollow)
Notochord
Pharyngeal slits
Muscular post anal tail
Chordate body plan .... continued
Notochord - a hydrostatic organ with fluid filled cells/ spaces contained in a fibrous sheath. Segmented muscles act on notochord to produce undulating motion>
Fibrous tube, loosely packed, fluid filled, allows for undulating swimming
Chordate body plan ... continued
Dorsal hollow nerve cord - as opposed to ventral in protostomes
Hollow due to unique ontogeny (origin) forms brain and spinal cord
develops from a plate of dorsal ectoderm that invaginates into a tube
Chordate body plan ... continued
Pharyngeal slits - openings from the pharynx to the body wall
filter feeding in protochordates, lated used for respiration in most vertebrates
homologous
Chordate body plan ... continued
muscualar postanal tail - with notochord and segmented musclture, provides very effective propulsion
Chordate body plan ... continued
endostyle - tissue along pharynx that accumulates iodine.
Mucus production in non vertebrates, hormonal in most vertebrates (thyroid)
ventral surface makes mucus
chordates are upside down hemichordates
Chordate body plan ... continued
pharyngeal pouch
Urochordata
Known as the sea squirts or tunicates
tunics are the only animals able to synthesise cellulose like plants
They have concentrate vadium in their blood cells - thought to be used of respiration?
Tadpole larval stage that disperses and most with distinct adult stage
all chordate characters apparent in larval stage
Ventral endostyle generates mucus and food collects dorsally
Urochordata: Ascidiacea (200 species)
Sessile
can be solitary or colonial
Hermaphrodites
Metamorphosis tadpole larvae short lasting
Urochordata: Larvacea (70 species)
Planktonic
adults retain some larval features - might be derived from ascidian larval forms
all species except 1 monoecious but protandrous
Live in a secreted mucus house
exceptional filter feeders (can eat bacteria)
Urochordata: Thaliacea (70 species)
free living, planktonic
derived from ascidians
Jet propulsion using feeding current - excurrent and incurrent on opposite sides of body and used for propulsion
Cephalochordata
Pikaia - an early cephalochordate from the burgess shale (good for preservation) in alberta (Middlecambrian) (114 specimens)
These fossils may have had a brain because there was evidence of swelling in the nervecord
They also had tentacles which is not usually seen
Cephalochordata: Yunnanozoon
from the lower cambrian of China, might have been an early vertebrate
This was the beginning of multicellular animals in this time frame
Cephalochordata
Adults very closely match the basic chordate body plan, but no distinct brain, eyes or neural crest tissue.
Filter feeders most sessile unless they are disturbed (burrow into the sand and chill waiting for food)
they filter feed in a similar manner to urochordates with an atrium developed from metapleural folds and atriopore find and fin rays but on homologous to those in fishes
Caecum/ hapatic diverticulitum - precursor to liver and pancreas
Cephalochordata contd
Laravel with simple mouth and exposed pharyngeal slits
metapleural folds encase the pharyngeal region to create an atrium and mouth parts at metamorphosis
Unusual development of pharynx - develops 1 side first then wraps around
Garstangs Auricularian hypothesis was influential
he thought the postanal tail was cool because the tunicates look the same in adult vs larvae but the larvae has a tail