Lecture 20 Flashcards
Deuterostomia characteristics
- bilateral symmetry
- triploblastic
- radial, indeterminate cleavage
- enterocoelous coelom
- blastopore does not become mouth
Deuterostomia 2 phyla
- Echinodermata (7000)
2. Chordata
Phylum Echinodermata
sea stars, sea urchins, sea lilies, sea cucumbers, all aquatic
echinodermata morphology
- thin epidermis covers endoskeleton made of many ossicles
- pentaradial symmetry (larvae bilaterally symmetrical) possibly evolved with Hox genes
- oral and aboral sides
- unique water vascular system
- tube feet for locomotion, feeding, gas exchange
- diffuse nervous system with no brain
ossicles
small calcareous plates, can be close or widely distributed, give prickly texture
water vascular system
network of hydraulic canals branching into extensions called tube feet, connects to sea water via special porous ossicle called the madreporite, fluid in the canals is sea water plus extra potassium, and some proteins plus free-roaming cells
echinodermata reproduction
- usually separate sexes
2. most engage in broadcast spawning (but larvae are brooded if internal fertilization)
broadcast spawning
fertilization occurs in open water, larva is planktonic
3 main echinoderm classes
- Asteroidea
- Crinoidea
- Holothuroidea
class asteroidea
sea stars/starfish, walk on tube feet, predatory
class crinoidea
sea lilies, feather stars, oral side faces up, suspension feeders
sea lilies
stalked and mostly sessile crinoids
feather stars
crinoids that lack stalks and walk using arms
class holothuroidea
sea cucumbers, secondarily bilaterally symmetrical, tube feet around mouth elaborated as feeding tentacles, skeleton reduced to scattered ossicles
larval cloning
echinoderms important models for studies of deuterostome-style development
phylum chordata 4 synapomorphies
- notochord
- dorsal hollow nerve cord
- pharyngeal slits/clefts
- muscular post-anal tail
notochord
flexible rod located dorsally between the digestive tube and the nerve cord, adds stiff but not rigid support along body, present in all chordate embryos and some adults (adults of most vertebrates reduced to pads between
vertebrae)
dorsal hollow nerve cord
unique to chordates (nerve cords in other animals are
solid, ventral), develops from plate of ectoderm dorsal to notochord, plate rolls into tube during embryonic development, anterior portion develops into brain
in most chordates
pharyngeal slits/clefts
slits connect pharynx (posterior to mouth) to external
environment, function as suspension-feeding devices in many invertebrate chordates, in aquatic vertebrates, are
gill slits, in terrestrial vertebrates pharyngeal clefts do not turn into slits, but the homologous pharyngeal pouches are important in structuring parts of head and neck
muscular post-anal tail
most adult chordates have muscular tail posterior to anus (most non-chordates have digestive tract that extends nearly whole length of body), tail provides propulsive force in swimming species
segmentally arranged muscles
present in all chordates except Urochordata, develop from blocks of mesoderm along notochord, arranged in chevrons, contraction causes notochord to flex from side to side (swimming), thus chordates are segmented
2 groups invertebrate chordates
- cephalochordata (25)
2. urochordata (1250)
cephalochordata
lancelets, amphioxus, marine, suspension feeders
urochordata
tunicates, salps, marine, adults are mostly sessile suspension feeders, tadpole larvae have all 4 synapomorphies and are active swimmers with muscular tail, adult has enormous pharyngeal basket with many slits, some planktonic, some permanently in larval form (paedogenesis)
paedogenesis
attaining reproductive adulthood while retaining morphology of juvenile
