Lecture 14 - hemichordates + chordates Flashcards
hemichordates cavity?
coelomates
2 groups of hemichordates
1) Enteropneusts - acorn worms
2) pterobranchs - sea angels
where are you likely to find acorn worms?
in muddy deposits but can live in various places
3 parts of acorn worm body
1 - proboscis - collects food - deposit feeder
2 - collar - concentration of nervous tissue
3 - trunk - gill slits for respiration found here
acorn worm nervous system
nerve net
acorn worm larval stage
tornria - similar to echinoderms
3 facts about pterobranchs
- very small
- sessile
- colonial
why are pterobranchs in the same group as acorn worms
they also have proboscic, collar and trunk
how do they protect themselves
withdraw their lopophore into their secreted case
what are sea angels traced back too
graptolites (cambrian - devonian)
what are hemichordates 5 resemblance to chordates
- no notochord
- no tail
- nervous tissue can be hollow but not dorsal nerve chord
- collect food externally dont use gills for feeding
- do have gill slits
what are hemichordates 3 resemblance to echinoderms
- similar larval stages
- similar nervous system
- some fossil forms are believed to have gill slits
4 basic features of chordates
- notochord - between gut and nervous system providing support for muscle contraction
- dorsal hollow nerve chord
- gill slits - feeding and respiration
- post anal tail
what are the 3 groups of chordates?
- urochrodates (tunicates)
- cephlachordates (lancelets)
- invertebrates
describe urochordates
- tadpole larval stage where they have all the characteristic feature of chordates - after metamorphis they lose all chordate features
