Cnidaria and Ctenophora

Question 1

How can animal body plans be characterized?

Answer 1

• Number of germ layers (no germ layers, diploblastic, triploblastic)
• Types of body cavities (coelomate, pseudocoelomate, acoelomate, complete gut, blind gut)
• Organismal complexity (protoplasmic, cellular, cell-tissue, tissue-organ, organ-system)
• Symmetry (no symmetry, spherical, radial, biracial, bilateral)

Question 2

What are the types of symmetry?

Answer 2

• Asymmetrical
• Spherical (ball shaped)
• Radial (tube or vase like)
• Biradial (radial with an additional paired structure)
• Bilateral (right and left sides)

Question 3

Explain asymmetrical

Answer 3

no symmetry

Question 4

Explain spherical symmetry

Answer 4

• Any plane passing through the center divides the body into mirrored halves
• Best suited for floating and rolling

Question 5

Explain radial symmetry

Answer 5

• Body divided into similar halves by more than two planes passing through the longitudinal axis
• Can interact with the environment in all directions
  Usually sessile, free floating, or weakly swimming animals

Question 6

Explain biradial symmetry

Answer 6

• Variant form of radial symmetry

- Radially symmetrical with the exception of a body part that is paired

Question 7

Explain bilateral symmetry

Answer 7

• Divided along a sagittal plane into two mirror portions forming right and left halves
• Much better for directional (forward) movements
• Associated with cephalization
• Also has mouth in front to allow for more efficient feeding and detection of prey

Question 8

What is cephalization?

Answer 8

The differentiation of a head region and the concentration of nervous tissues and sense organs in the front area

Question 9

What are the planes of symmetry?

Answer 9

• Frontal plane (coronal plane)
  Divides body into dorsal and ventral halves
• Sagittal plane
  Divides body to right and left
• Transverse plane (cross section)
  Divides body into anterior and posterior halves

Question 10

Regions of bilaterally symmetrical animals

Answer 10

• Anterior (head end)
• Posterior (tail end)
• Dorsal (back side)
• Ventral (bottom or belly side)
• Medial (midline of body)
• Lateral (right and left sides)
• Distal (parts farther from the middle of body)
• Proximal (parts are nearer the middle of body)

Question 11

What are Cnidaria and Ctenophora?

Answer 11

• Phylum Cnidaria: hydroids, anemones, jellyfish and corals
• Radial symmetry
• Cell tissue level of biological organization (some organs may occur)
• Diploblastic
• Blind gut

Question 12

What is the Phylum Cnidaria?

Answer 12

• Mostly sessile or slow moving
• Efficient predators
• Algae frequently live as mutualists with Cnidarians
• Mostly marine, some freshwater, no terrestrial
• Abundant in shallow marine habitat

Question 13

What are the classes in the Phylum Cnidaria?

Answer 13

• Class Hyrdozoa (includes hydroids, fore corals, Portuguese man of war)
• Class Scyphozoa (true jellyfish)
• Class Cubozoa (box jellyfish)
• Class Anthozoa (largest class and includes sea anemones and corals)

Question 14

What are the classifications?

Answer 14

• Metazoa
  All animals
• Eumetazoa
  Multicellular animal with distinct germ layers
  Has true tissues
  Includes Cnidaria and Ctenophora but excludes Porifera
  All eumetazoans other than Cnidarians and Ctenophores
  exhibit primary bilateral symmetry

Question 15

What are there forms?

Answer 15

• Two morphological types
  Polyp (sedentary or sessile)
  Medusa (floating or free swimming)
• Many Cnidarians are dimorphic; exhibit both polyp and medusa forms
• In some species, only one form exists
• Both medusa and polyp forms are diploblastic (two tissue layers)
• In between tissue layers is a jellylike layer of mesoglea
• Mesoglea is thicker in the medusa form (gives it buoyancy)
• Medusae are commonly called jellyfish or jellies

Question 16

What is the polyp form?

Answer 16

• Tube shaped
• Tend to be sedentary or sessile
• Mouth surrounded by tentacles
• Can be attached to substratum by a pedal disc

Question 17

What is the medusa form?

Answer 17

• Umbrella shaped
• Floating or free swimming
• Mouth centred on concave side
• Tentacles extend from rim of umbrella shape

Question 18

What is the Cnidarian physiology?

Answer 18

• Respiration (by diffusion)
• Digestion
  Mouth opens into gastrovascular cavity
  Incomplete or blind gut
  Use both extracellular and intracellular digestion (undigested
  particles carried back to gastrovascular cavity by amoeboid
  cells)

Question 19

What is extracellular digestion?

Answer 19

enzymes discharged into gastrovascular cavity

Question 20

What is intracellular digestion?

Answer 20

phagocytosis of food particles

Question 21

What is the reproduction of Cnidarians?

Answer 21

• Varies among classes
• Most have free swimming planar larva
• Planula settles and metamorphoses into a polyp
• Polyps can reproduce asexually and sexually
  Into more polyps or into medusae
  Colonies form when polys reproduce asexually but stay
  attached
  Polyps within colony specialize for certain functions
• Medusae reproduce sexually

Question 22

What is the lifer cycle of Aurelia?

Answer 22

• Sperm fertilizes egg in gastric pouch
• Zygote develops on arms of female
• Planula larva attaches and becomes a scyphistoma (polyp form)
• Scyphistoma can bud to form other polyps (asexual reproduction)
• Becomes a strobila
• Releases saucer like buds called ephyrae
• Ephyrae into mature jellyfish (medusa form)

Question 23

What is their locomotion?

Answer 23

• Some polyps are permanently attached (sessile)
• Hydra and sea anemones can move slowly by gliding on pedal disc
  Hydra can also use a measuring worm movement
  Sea anemones occasionally swim
• Medusae can move freely
  Swim by contracting the bell
  Usually contract several times and move generally upward
  Then sink slowly

Question 24

A fearsome tiny weapon

Answer 24

• All Cnidarians have tentacles with stinging cells at tip
• Stinging cells are called cnidocytes
• Cnidocytes (cell that holds cnida)
• Cnida
  Singing organelle
  Nematocyst: most common type of cnida
  Many nematocyst have a toxin which paralyses prey
• Cnidocil
  Triggers the nematocyst to fire

Question 25

Explain the class Hydrozoa

Answer 25

• Typical life cycle includes asexual polyp and sexual medusa stage
• Freshwater hydra have no medusa stage
• Others have no polyp stage and occur only as medusa

Question 26

Explain class Scyphozoa

Answer 26

• True jellyfish
• Dioecious
• Internal fertilization
• Exhibit medusa and polyp form during life cycle
  Medusa reproduces sexually
  Polyp reproduces asexually

Question 27

Explain class Cubozoa

Answer 27

• Box jellyfish
• Medusa is prominent form
  Polyp is often uncharacterized
• Medusa bells are almost square
• Tentacles occur at corners of square
• Strong swimmers and predators
• Stings from some species can be fatal to humans

Question 28

Explain class Anthozoa

Answer 28

• Polyps with a flower-like appearance: sea anemones, corals, sea fans
• No medusa stage
• Sexual and asexual reproduction occur in polyp phase
• All marine
• Solitary or colonial

Question 29

What is the Phylum Ctenophora?

Answer 29

• Cell tissue level of biological organization (some organs may occur)
• Diploblastic
• Blind gut
• Approx. 150 species
• All marine, especially in warm waters
• Commonly called sea walnuts or comb jellies
• Name comes from comb-like plates that they use for locomotion (combs are made from fused cilia)
• Do not have nematocyst
  Colloblasts line tentacles (release sticky substance instead of
  venom
  One species recycles nematocysts from Cnidarian medusa