Lecture 27 Echinoderms & Chordates

Question 1

what consists of the deuterstomia clade?

Answer 1

echinoderms and chordates

Question 2

what are echinoderms?

Answer 2

sea stars and sea urchins

calcareous skeleton

Question 3

what are chordates?

Answer 3

include vertebrates

Question 4

what are characteristics of deuterstomia?

Answer 4

• bilaterally symmetrical, triploblastic
• radial indeterminate cleavage
• anus is from blastopore

Question 5

how are deuterstomia defined by

Answer 5

• defined by DNA SIMILARITIES

Question 6

what are echinoderm characteristics?

Answer 6

• 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

Question 7

what are tube feet?

Answer 7

d

Question 8

what are echinoderm characteristics?

Answer 8

• 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

Question 9

what are tube feet?

Answer 9

network of hydraulic canals branching into extensions that function in locomotion and feeding
-connects to sea water via special porous ossicle : madreporite

Question 10

what three classes of echinoderms do we focus on?

Answer 10

• asteroidea (starfish sea dasies)
• echinoidea (sea urchins and sand dollars)
• holothuroidea (sea cucumbers)

Question 11

what is class asteroidea?

Answer 11

• 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

Question 12

what is class echinoidea?

Answer 12

• 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

Question 13

what is class holothuroidea?

Answer 13

• 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

Question 14

what is phylum chordata?

Answer 14

• 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

Question 15

what are the four key synapomorphies of chordates?

Answer 15

• notochord
• dorsal, hollow nerve cord
• pharyngeal slits or clefts
• muscular, post-anal tail

Question 16

what is the notochord?

Answer 16

• a longitudinal, flexible rod located dorsally between the digestive tube and nerve cord

Question 17

what is the notochord?

Answer 17

• 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

Question 18

what is the dorsal, hollow nerve cord?

Answer 18

• 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

Question 19

what are pharyngeal slits or clefts?

Answer 19

• 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

Question 20

what is the muscular post-anal tail?

Answer 20

• tail contains skeletal elements and muscles – propulsive force, rudder, balance
• in many it is greatly reduced during embryonic development

Question 21

what is the muscular post-anal tail?

Answer 21

• tail contains skeletal elements and muscles – propulsive force, rudder, balance
• in many it is greatly reduced during embryonic development

Question 22

what are other characteristics of chordates?

Answer 22

segmentation: ex muscle blocks and vertebral column (not seen in urochordata)

Question 23

what occurs instead of segmentation in urochordata?

Answer 23

• muscles arranged in chevrons

- contraction allows swimming

Question 24

what is subphylum cephalochordata?

Answer 24

deuterstomes - chordates - LANCELETS

- marine sedentary filter feeders that retain characteristics of chordate body plan in adults

Question 25

what is subphylum urochordata?

Answer 25

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