deuterostomes I; starfish, sea squirts and amphioxus Flashcards
echinoderms classes
starfish sea urchins brittle stars sea cucumbers sea lillise
cleavage types
spiral cleavage
radial cleavage
spiral cleavage
new cells in cell division sit above grooves of old 4 cells
radial cleavage
new cells in cell division sit directly on top of four old cells
gastrulation
hollow ball of cells forms (blastula) and then moves inwards create a blastopore. This then develops further into an indented tube that will form the gut
animals with spiral cleavage
the blastopore will form the mouth at the end of the gut and create a mouth and anus end
- are protostomes; ‘first mouth’
animals with radial cleavage
blastopore marks the rear end of embryo where anus forms
- are deuterostomes; ‘second mouth ‘
bilaterian animals
protostome mode of development; lophotrochozoa and ecdysozoa
bilateria without protostome development
insects and nematodoes; have neither radial or spiral cleavage
deuterostomia grouping
some but not all animals with radial cleavage and secondary mouth formation
three major groups of deteurostomia
echinodermata
hemichordata
chordata
basal animals: chindaria
jellyfish in cnidaria
- no obvious left or right symmetry
- four fold symmetry
echinoderms evolution
- ‘number five’ pattern evlution
- include starfish and brittle stars and sea urchins and sea cucumbers and crinoid/sea lillies
has fluid filled canal in body called water vascular system
starfish evolution
five aerms moves with tiny tub efeed are predatory and hunt bivalve molluscs stomach secretes enzymes to weaken clam has fluid filled canal in body called water vascular system
brittle stars
graze on debris and detritus
sea urchins/sea cucumbers
defensive spines or elongated body
five zones around body
have tube feed zones
crinoids or sea lillies
filter feeding animals with mouth on top and five featehred arms
pentaradial symmetry
evolved from bilateral symmetry
- echinoderms LARVAE biltaeral; metamophirsis changes this to 5
- echinoderm fossils have found with several symmetries
- echinodermiata are within the bilateria; same common acnestory
hemichordates examples
acorn worms
pterobranchs
hemichordates are
non segemented
radial cleavage and secondary mouth formation
similar larave to echinoderms
small/filter food using pharanygeal slits
shared ancestor of hemichordates and vertebrates
pharyngeal slits/gills forfood/oxygen
pterobranch
miniscule tube dwelling animals with tentecales
tunicates
sea squirts/ascidians; form part of the chodata; urochordata
- amoprhous apperance
- tunic (tough outer layer) contains cellulose
- have tiny cilia
- stationionary filter feeder as adult
tunicate reclassifciation
originalyl considered molluscs; turns out they are actually chordata due to embryonic/larvae development of sea squirt starts out as tadpoles and then become sessile, filter feeders
- have a notochord
larvaceans
living relatives of sea squirts; DONT become filterfeeders but remain as larvae
chordata groups (Supphyla)
- tunicates (sea squirts and larvaceans); urochordata
- vertebrates
- cephalochordates (amphioxus)
characteristic features of chordates
- brain
- nerve cord
- notochord
- pharyngeal slits/holes
chordate feature sin fish
gills develop form pharyngeal slits
notochord becomes bone during development
chordate feature in human
we have slits in development; lose these into grooves on embryo
notochord/spinal cord
cephalochordates
or ‘amphioxus’; fish like in apperance (burrowing),
few cm in length,
have a notocord as stiffening rod with contrasting muscles for swimming,
pharyngeal slits for filtering algea
ernst haeckel on amphioxus
are they degenerate verterbtates? however represent link between invertebrates and vertertabes; features in ruidmentary form
