Lecture 27 Echinoderms & Chordates Flashcards
what consists of the deuterstomia clade?
echinoderms and chordates
what are echinoderms?
sea stars and sea urchins
calcareous skeleton
what are chordates?
include vertebrates
what are characteristics of deuterstomia?
- bilaterally symmetrical, triploblastic
- radial indeterminate cleavage
- anus is from blastopore
how are deuterstomia defined by
- defined by DNA SIMILARITIES
what are echinoderm characteristics?
- slow moving and sessile
- most have radial symmetry with multiples of five (pentaradial symmetry) except for sea cucumbers – secondarily bilateral
- larvae have bilateral symmetry
- mouth at centre of arms and faces down
- thin epidermis covers endoskeleton of ossicles (hard calcareous plates may have spines)
- unique WATER VASCULAR SYSTEM
what are tube feet?
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what are echinoderm characteristics?
- slow moving and sessile
- most have radial symmetry with multiples of five (pentaradial symmetry) except for sea cucumbers – secondarily bilateral
- larvae have bilateral symmetry
- mouth at centre of arms and faces down
- thin epidermis covers endoskeleton of ossicles (hard calcareous plates may have spines)
- unique WATER VASCULAR SYSTEM
- tube feet
- diffuse NS with no central brain/ganglia
- separate sexes
- broadcast spawning – external sexual reproduction
what are tube feet?
network of hydraulic canals branching into extensions that function in locomotion and feeding
-connects to sea water via special porous ossicle : madreporite
what three classes of echinoderms do we focus on?
- asteroidea (starfish sea dasies)
- echinoidea (sea urchins and sand dollars)
- holothuroidea (sea cucumbers)
what is class asteroidea?
- sea stars or starfish – five or more arms radiating from a central disk
- undersurface of each arm bears tube feet which grip substrate with adhesive chemicals
- predatory – tube feet pry open bivalves
- regeneration, can regrow lost arms
what is class echinoidea?
- sea urchins and sand dollars
- no arms but have five rows of tube feet
- slow moving - spines used for locomotion and protection
- sea urchins feed on seaweed using a jaw-like structure on their underside
what is class holothuroidea?
- sea cucumbers
- elongated (in oral-arboral axis)
- secondarliy bilaterally symmetrical
- 5 rows tube feet, some around mouth to serve as feeding tentacles
- lack spines - endoskeleton reduced to scattered ossicles
- deposit or suspension feeders
- shoot out internal organs if disturbed
what is phylum chordata?
- bilaterian animals that belong to clade deuterstomia
- coelomates with segmented bodies
- evolved separately for the last 500 million years
- more than 90% have backbones – thus vertebrates
- chordates comprise all vertebrates, and two groups of invertebrates – urochordates and cephalochordates
what are the four key synapomorphies of chordates?
- notochord
- dorsal, hollow nerve cord
- pharyngeal slits or clefts
- muscular, post-anal tail
what is the notochord?
- a longitudinal, flexible rod located dorsally between the digestive tube and nerve cord
what is the notochord?
- a longitudinal, flexible rod located dorsally between the digestive tube and nerve cord
- provides skeletal support
- present in all chordate embryos
- in most vertebrates, more complex jointed skeleton develops – adult retains only remnants of embryonic notochord – reduced to disks between vertebrae
what is the dorsal, hollow nerve cord?
- unique to chordates (in other animals it is solid and ventral)
- develops from a plate of ectoderm that rolls into a tube dorsal to the notochord
- nerve cord develops into CNS – brain and spinal cord
what are pharyngeal slits or clefts?
- in most, grooves in pharynx posterior to mout – allow water that enters mouth to exit without continuing through the entire digestive tract
- fxn: suspension feeding structure in invertebrate chordates, gas exchange, develop into parts of the ear, head and neck in tetrapods
what is the muscular post-anal tail?
- tail contains skeletal elements and muscles – propulsive force, rudder, balance
- in many it is greatly reduced during embryonic development
what is the muscular post-anal tail?
- tail contains skeletal elements and muscles – propulsive force, rudder, balance
- in many it is greatly reduced during embryonic development
what are other characteristics of chordates?
segmentation: ex muscle blocks and vertebral column (not seen in urochordata)
what occurs instead of segmentation in urochordata?
- muscles arranged in chevrons
- contraction allows swimming
what is subphylum cephalochordata?
deuterstomes - chordates - LANCELETS
- marine sedentary filter feeders that retain characteristics of chordate body plan in adults
what is subphylum urochordata?
deuterstomes - chordates - tunicates
- more closely related to other chordates than are lancelets
- tadpole larvae stage has all 4 chordate synapomorphies
- adults DONT look like chordates
- filter water through mucous covered pharyngeal basket to filter food
