Lecture 20: Echinoderms, Hemichordates, Chordates Flashcards
what makes a deuterostome?
- “mouth second”
- some are segmented
- internal segments
- monophyletic
ancestral deuterostomes: homalozoans
-have traits that we see in echinoderms and chordates (indicates that they branched off of each other after homalozoans).
echinoderms
- pentaradial symmetry in adults
- characterized by internal skeleton
- very closely related to us.
pentaradial symmetry
-5 axes of symmetry or multiple of 5
echinoderm larvae
-have bilateral larvae
water vasculature system
- water filled canals leading to the tube feet
- used for feeding, gas exchange, locomotion
madreporite and tube feet
- “mother pore”
- water flows into ring canal and circulated throughout each tube foot
- tube feet also used for attachment
oral surface
- headless bc bilateral
- it’s underneath (what they crawl on)
aboral surface
opposite of oral surface
asexual reproduction in echinoderms
-form of regeneration, many can regenerate lost parts
sexual reproduction in echnioderms
-gametes released into water (external fertilization)
extinct echinoderms
-20 classes are extinct
three groups of echinoderms
- crinoids
- echinozoans
- asterozoans
crinoids
types: sea lilies and feather stars
asterozoans
types: sea stars and brittle stars
sea lilies
- don’t move
- have main body and a bunch of arms
feather stars
-attach to surface with arms, can walk/swim
sea stars
- type of starfish
- a very important predator
- live in a range of marine environments
brittle stars
- thinner arms made of jointed hard plates
- arms are flexible and have no “suckers”
- largest group of living echinoderms
- nocturnal, can freely swim
echinozoans
-types: sea cucumbers, sea urchins, sand dollars
sea cucumber
- harmless, genetically similar to all other echinoderms
- when you cut it open, you can its pentaradial symmetry
sea urchin
- ball and socket joint connected spines
- allows them to rotate
- they pivot/sting threats
sand dollar
- flattened disk
- pentamerous
hermichordates
- sister taxa to echinoderms
- have a 3 part body plan
- types: acorn worm (up to 2m long)
chordate traits
- dorsal Hollow nerve cord
- notochord
- pharyngeal gill slits
- post-anal tail
- All seen best during embryonic development
dorsal hollow nerve cord
- runs beneath dorsal surface
- develops into brain and spinal nerve cord
notochord
- place just above gut and just below dorsal hollow nerve cord
- plays a role in nervous system development or becomes part of the vertebral column
pharyngeal gill slits
- connects pharynx to external environment and allows us to swallow
- pouches never open on terrestrial vertebrates
- it’s an ancestral trait that was lost in echinoderms but present in chordates
post-anal tail
-have it at some point in development every chordate has a tail protruding away from the anus
chordate segmentation
-all chordates are segmented
non-vertebral chordate groups
-lancelets and tunicates
non-vertebral chordate larvae and chordate traits
-the larvae have gill slits, notochord, dorsal hollow nerve cord, and post-anal tail
lancelets
-small, notochord helps them burrow
tunicates
- aka sea squirts
- vary in size
- many form colonies through asexual budding
