Echinodermata & Vertebrate (Beginning)

Question 1

What distinguishes the Protostomia?

Answer 1

• Spiral mosaic cleavage
• Mouth from blastopore
• Coelom from schizocoely

Question 2

What distinguishes the Deuterostomia?

Answer 2

• Radial regulative cleavage
• Anus from blastopore
• Coelom by enterocoely

Question 3

What is the Phylum Chaetognatha?

Answer 3

• Arrow worms
• Pelagic marine predators
• Has been variously placed in Protostomia and Deuterostomia
• Developmental characters suggest that they are deuterostomes
  anus arises from blastopore
  coelom formation is enterocoelous
• Molecular data suggests that they are protostomes
  additionally, cleavage is similar to crustaceans and nematodes

Question 4

What is the Phylum Hemichordata?

Answer 4

• Formerly considered a subphylum of chordates
  reclassified because they do not have a true notochord
• Worm like bottom dwellers

Question 5

What is the Phylum Echinodermata?

Answer 5

• Sea stars, brittle stars, sea urchins, sea cucumbers and sea lillies
• A puzzle to biologists (strange symmetry)
• Echinoderms (and hemichordates) are the closest living relatives to chordates

Question 6

What are the key characteristics of the Phylum Echinodermata?

Answer 6

1) Endoskeleton
2) Pentaradial symmetry
3) Water vascular system

Question 7

Explain the spiny endoskeleton

Answer 7

• Skeleton or supporting framework within the living tissues of an organism
• Contrasts with exoskeleton
• Made of small calcareous plates bound together with connective tissue
• This endoskeleton is beneath the epidermis, but calcareous spine poke through
• Echinoderms are unappealing prey (exception: a few fish with strong teeth, other echinoderms, sea otters eat sea urchins)

Question 8

Explain the pentaradial symmetry

Answer 8

• Radial symmetry in five parts
• Some sea stars have more than five arms (start development with five)
• Bilateral symmetry is adaptive for motile animals
• Radial symmetry is adaptive for sessile animals
• Echinoderms are free moving but radial (unusual combination)
• Larvae of echinoderms are bilaterally symmetrical
• Earliest echinoderms were likely bilaterally symmetrical
  at some point during evolution they become sessile and radial
• Evolution has favoured the motile descendants of these sessile organisms
  even though they are still radial
• Some groups have secondarily evolved a superficial bilateral organization
  they still have pentaradial organization of skeletal and most organ systems

Question 9

Explain the water vascular system

Answer 9

• Unique to echinoderms
• Comprised of canals and specialized tube feet
• Functions: locomotion, food gathering, respiration and excretion

Question 10

What are the classes to the phylum Echinodermata?

Answer 10

Asteroidea (sea stars)
Ophiuroidea (brittle stars and basket stars)
Echinoidea (sea urchins, sand dollars, heart urchins)
Holothuroidea (sea cucumbers)
Crinoidea (sea lilies and feather stars)

Question 11

What is the class Asteroidea

Answer 11

• Sea stars
• Central disc that merges with tapering arms
• Pentaradial symmetry (typically five arms, may have more)
• Oral surface (near mouth)
  on underside of body
• Aboral surface (opposite mouth)
• Ambulacral groove runs along the oral surface of each arm
• Tube feet are found along the ambulacral grooves
• Madreporite is the structure where water enters the water vascular system

Question 12

What is the water vascular system of the Asteroidea?

Answer 12

• Systen opens to the outside through the madreporite (on aboral surface)
• Madreporite leads to a series of canals
• Canals are connected to the podia (tube feet)
• Podia stick through the ossicles in the ambulacral groove
• Muscles and valves control the amount of fluid flowing into the podia (creates movement)

Question 13

What is the feeding and digestive system of the Asteroidea?

Answer 13

• Many sea stars are carnivorous
  feed on molluscs, crustaceans, polychaete, echinoderms, and sometimes small fish
• The lower part of the stomach can be everted through the mouth during feeding
• Steps to eating a clam (if you are a sea star)
  Wrap yourself around prey
  Attach podia to valves and pull apart
  Insert soft everted stomach into the gap between valves
  Begin digestion
  Pull stomach back in

Question 14

What is the regeneration of the Asteroidea?

Answer 14

• Sea stars can regenerate lost parts
• Regeneration can take several months
• Some species can regenerate a whole new sea star from a severed arm (fragmentation)
  For most asteroids, the arm must contain a portion of the central disc
  In other species a whole individual can regenerate form an arm
• fisherman used to kill sea stars collected from their oyster beds by chopping them in half (not a good idea)

Question 15

What is the reproduction and development of the Asteroidea?

Answer 15

• Sexual reproduction
  Dioecious
  External fertilization
• Most sea stars produce free swimming planktonic larvae
  The larvae are bilaterally symmetrical
  Metamorphosis involves a dramatic reorganization
  Bilateral larva becomes a radial juvenile
• Asexual reproduction in some species
  By fragmentation and regeneration

Question 16

What is the class Echinoidea?

Answer 16

• Sea urchins, sand dollars, heart urchins
• Dermal ossicles have become closely fitting plates which form a shell
• Spines protrude in living specimens (long in sea urchin, shorter and softer in sand dollars and heart urchins)
• Lack arms, but have the typical pentamerous plan of echinoderms

Question 17

What is the body symmetry of the Echinoidea?

Answer 17

• Most living species are regular (radial symmetry)
• Sand dollars and heart urchins are irregular
  radial symmetry
  secondary bilateral symmetry

Question 18

What is the class Holothuroidea?

Answer 18

• Sea cucumbers
• Odd animals in an odd phylum
• Elongated oral aboral axis
• Ossicles are reduced (soft bodied)
• Pentaradial symmetry
• Secondarily evolved a degree of bilateral symmetry (as adults)
  all echinoderm larvae are bilaterally symmetrical
• Some species cast out a part of their viscera (guts) as a defence mechanism
• Strong muscular contraction either ruptures the body wall or everts its contents through the anus
• Lost parts are regenerated

Question 19

What are characters of Chordates?

Answer 19

• Bilateral symmetry
• Anterior posterior axis
• Complete gut
• Coelom “tube within a tube” arrangement
• Metamerism
• Cephalization
• Chordates are deuterostomes, so also
  Radial cleavage
  Anus derived from blastopore
  Coelom formed by enterocoely (but most vertebrates from coelom by schizocoely)

Question 20

What are the Protochordata?

Answer 20

• Not a monophyletic group
• Includes two subphylum
  Urochordata (tunicates)
  Cephalochordata (lancelets, ‘amphioxous’)
• These subphyla are the only invertebrate chordates

Question 21

What is the subphylum Urochordata?

Answer 21

• Commonly called tunicates
• Most sessile as adults, some free living
• The name Tunicate describes the tough, nonliving tunic (or test) that surrounds the animal
• Only the larval form bears all the chordate hallmarks
• solitary or colonial

Question 22

What is the subphylum Cephalochordata?

Answer 22

• Lancelets
• Originally bore the generic name Amphioxus
• Modern survivors of an ancient chordate lineage
• Slender, laterally compressed, translucent animals
• Inhabit sandy sediments of coastal waters
• 5 distinct characteristics of chordates but in simple form
• Lack features found in true vertebrates
  no brain
  no true vertebrae

Question 23

What are the 5 hallmarks of the Phylum Chordata?

Answer 23

1) Notochord
2) Dorsal hollow nerve cord
3) Pharyngeal pouches or slits
4) Endostyle for filter feeding
5) Postanal tail for propulsion

Question 24

Explain the notochord

Answer 24

• Flexible, rod like body of fluid filled cells enclosed by a fibrous sheath
• All members of phylum Chordata possess a notochord
• Can be restricted to early development
• Organizational role in nervous system development
• Persists throughout life in jawless vertebrates and protochordates
• Becomes the vertebral column in all jawed vertebrates

Question 25

Explain the dorsal hollow nerve cord

Answer 25

• Nerve cord is dorsal to the digestive tract and notochord
• Nerve cord is hollow
• In craniates
  Anterior end of nerve cord becomes enlarged to form the brain (the rest is the spinal cord)
  Nerve cord passes through vertebrae and the brain is surrounded by a bony or cartilaginous cranium
• Invertebrates can also have a nerve cord, but it is ventral to the digestive tract and solid

Question 26

Explain the pharyngeal pouches/slits

Answer 26

• Openings that lead from the pharyngeal cavity to the outside (pharyngeal cavity = opening of the pharynx)
• Pharynx = the part of the digestive tract between the mouth and the esophagus that, in vertebrates, is common to both the digestive and the respiratory tracts
• They take on different forms in different groups

Question 27

How does the pharyngeal slits look in the protochordates?

Answer 27

Perforated pharynx functions as a filter feeding apparatus (original evolutionary role)

Question 28

How does the pharyngeal slits look in the aquatic chordates?

Answer 28

Pharyngeal slits bear gills used in gas exchange in some aquatic chordates

Question 29

How does the pharyngeal slits look in the tetrapods?

Answer 29

• Pharyngeal pouches are inly present in the embryonic stage
• Give rise to several different structures including Eustachian tube, middle ear cavity, tonsils, and parathyroid gland

Question 30

Explain the endostyle/thyroid gland

Answer 30

• Occurs in all chordates and no other animals
• Endostyle is present in protochordates and lamprey larvae
  The endostyle secretes mucus that traps food particles brought into the pharyngeal cavity
  Cells in the endostyle secrete iodinated proteins (homologous with the iodinated-hormone-secreting thyroid gland)
• Adult lampreys and remainder of vertebrates have thyroid glands
  Thyroid gland regulates metabolism and helps to produce and regulate other hormones

Question 31

Explain the postnatal tail

Answer 31

• In protochordates (larval tunicates and amphioxus), the postanal tail provides motility
• Increases in fishes
• Present in humans only as a vestige (the coccyx, a series of small vertebrae at the end of the spinal column)
• Most other mammals have a waggable tail as adults