Lecture 16 Flashcards

1
Q

Phylum Chaetognatha

A
  • “Arrow worms”
  • Pelagic marine predators
  • Has been placed in Protostomia and Deuterostomia
  • DEVELOPMENTAL characters suggest that they are deuterostomes
  • Anus arises from blastopore
  • Coleom formation is enterocoelous
  • MOLECULAR data suggests that they are protostomes
  • Additionally, cleavage is similar to crustaceans and nematodes
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2
Q

Phylum Hemichordata

A

do not have a true notochord

Wormlike bottom-dwellers

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3
Q

Phylum Echinodermata Key Characteristics (3)

A
  1. Endoskeleton
  2. Pentaradial symmetry
  3. Water vascular system
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4
Q

Spiny Endoskeleton of echinoderms

A

Endoskeleton
• skeleton or supporting frame work within the
living tissues of an organism
• Made of small calcareous plates (“ossicles”) bound together with connective tissue
• This endoskeleton is beneath the epidermis, but calcareous spines poke through
• Echinoderms are unappealing prey
Calcareous = composed of calcium carbonate

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5
Q

Predators of echinoderms

A

a few fish with strong teeth,other echinoderms, sea otters eat sea urchins

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6
Q

Pentaradial symmetry of echinoderms

A

Radial symmetry in five parts (‘penta’)
• Some sea stars have more than five arms
• Start development with five .: still pentaradial

HOWEVER
Larvae of echinoderms are bilaterally symmetrical
Earliest echinoderms were likely bilaterally symmetrical
Some groups (e.g. sea cucumbers, some sea urchins) have
secondarily evolved a superficial bilateral organization
They still have a pentaradial organization of skeletal and most organ systems

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7
Q

Water vascular system of echinoderms

A
  • Unique to echinoderms
  • Comprised of canals and specialized tube feet
  • Functions: locomotion, food gathering, respiration, and excretion
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8
Q

Classes of phylum echinodermata

A
  • Class Asteroidea: Sea stars
  • Class Ophiuroidea: brittle stars and basket stars
  • Class Echinoidea: Sea urchins, sand dollars, heart urchins
  • Class Holothuroidea: Sea cucumbers
  • Class Crinoidea: Sea lilies and feather stars
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9
Q

Class Asteroidea characteristics

A

Sea Stars
• Central disc that merges with tapering arms
• Pentaradial symmetry:
• Typically five arms, may have more (e.g.
sun stars)
• 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

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10
Q

Asteroidea: Water vascular system

A
  • System 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
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11
Q

Asteroidea: Feeding and digestive system

A
  • Many sea stars are carnivorous;
  • The lower part of 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
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12
Q

Asteroidea: Regeneration

A
  • Some species can regenerate a whole new sea star from a severed arm (Fragmentation)
  • For most asteroids, the arm must contain a portion (about 1/5th) of the central disc
  • In other species a whole individual can regenerate from an arm
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13
Q

Asteroidea: Reproduction & Development

A
  • 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)

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14
Q

Class Echinoidea characteristics

A

• 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 urchins, shorter and softer in sand dollars and heart urchins)
• Lack arms, but have the typical pentamerous plan of echinoderms

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15
Q

Class Echinoidea – body symmetry

A
  • Most living species are ‘regular’
  • Radial symmetry
  • Sand dollars and heart urchins are irregular
  • Radial symmetry + Secondary bilateral symmetry
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16
Q

Class Holothuroidea

A
  • 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
17
Q

Class Holothuroidea defense

A
  • Some species cast out a part of their viscera (guts) as a defense mechanism
  • Strong muscular contraction either ruptures the body wall or evert its contents through the anus
  • Lost parts are regenerated (takes time and energy)
18
Q

Characters of Chordates (7)

A
  • Bilateral symmetry
  • Anterior-posterior axis
  • Complete gut
  • Coelom “tube-within-a-tube” arrangement
  • Metamerism
  • Cephalization
  • Anus derived from blastopore

(Chordates are deuterostomes, so also… Radial cleavage!!)

19
Q

Protochordata

A
  • Not a monophyletic group
  • Includes two subphyla:
  • Urochordata (tunicates)
  • Cephalochordata (lancelets, ‘amphioxous’)
  • These subphyla are the only invertebrate chordates
  • i.e. they are chordates, but not part of Craniata (aka Vertebrata)
20
Q

Subphylum Urochordata

A

protochordata (chordata)
• 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

21
Q

Subphylum Cephalochordata

A

protochordata (chordata)
• Lancelets
• 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

22
Q

5 Hallmarks of the Phylum Chordata

A
  1. Notochord
  2. Dorsal hollow nerve cord
  3. Pharyngeal pouches or slits
  4. Endostyle for filter feeding
  5. Postanal tail for propulsion
23
Q

Notochord

A

• Notochord = Flexible, rod-like body of fluid-filled cells enclosed by a fibrous sheath
• All members of phylum Chordata posess a notochord
• Can be restricted to early development (e.g. vertebrates)
• Organizational role in nervous system development
• Persists throughout life in jawless vertebrates and
protochordates
• Becomes the vertebral column in all jawed vertebrates (i.e. Gnathostomata)

24
Q

Dorsal Hollow Nerve Cord

A

In all Chordates…
• Nerve cord is dorsal to the digestive tract and notochord • Nerve cord is hollow
In craniates (=vertebrates)…
• 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

Note: Invertebrates can also have a nerve cord, but it is ventral to the digestive tract and solid

25
Q

Pharyngeal Pouches or Slits

A
  • 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.
26
Q

different forms of Pharyngeal slits/pouches

A
  • Protochordates
  • perforated pharynx functions as a filter-feeding apparatus (original evolutionary role)

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

  • Tetrapods (four-limbed vertebrates)
  • pharyngeal pouches are only present in the embryonic stage
  • give rise to several different structures including Eustachian tube, middle ear cavity, tonsils, and parathyroid gland
27
Q

Endostyle or Thyroid Gland

A
  • 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