Lecture 12

Question 1

Types of Symmetry

Answer 1

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

Question 2

Planes of Symmetry

Answer 2

• 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 3

Regions of bilaterally symmetrical animals

Answer 3

• 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 4

Cnidaria & Ctenophora Characteristics

Answer 4

Cnideria: hydroids, anemones, jellyfish, corals
• Radial symmetry
• Cell-Tissue level of biological organization (some organs may occur)
• Diploblastic
• Blind gut

Question 5

Cnidaria characteristics

Answer 5

• 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 6

Classes in phylum cnideria

Answer 6

• Class Hyrdozoa
     Includes hydroids, fire corals, Portuguese
man-of-war
• Class Scyphozoa
      true jellyfish
• Class Cubozoa
         box jellyfish
• Class Anthozoa
        largest class
        Includes sea anemones, and corals

Question 7

Eumetazoa

Answer 7

Every metazoa except sponges; has true tissues, has distinct germ layers,exhibit primary bilateral symmetry

Question 8

cnideria Forms

Answer 8

• Polyp (or hydroid): sedentary or sessile
• Medusa (or jellyfish): floating or free- swimming
• 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 9

Can a cniderian exist in only one form?

Answer 9

YES! some experience both polyp and medusa in lifetime but some may only experience one

Question 10

Polyp Form

Answer 10

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

Question 11

Medusa Form

Answer 11

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

Question 12

Cnidarian physiology

Answer 12

• Respiration By diffusion
• Digests by Mouth openning into gastrovascular cavity
• Incomplete or ‘blind’ gut
• Use both extracellular and intracellular digestion

Question 13

Extracellular and intracellular digestion

Answer 13

• Extracellular digestion – enzymes discharged into gastrovascular cavity
• Intracellular digestion – phagocytosis of food particles
• Undigested particles carried back to gastrovascular cavity by amoeboid cells

Question 14

Cnidarian Reproduction

Answer 14

• Most have free-swimming planula larva
• Planula settles and metamorphoses into a polyp
• Polyps can reproduce asexually or sexually
• Medusas reproduce sexually

Question 15

Life cycle of Aurelia (moon jelly)

Answer 15

• 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 grow into mature jellyfish (medusa form)

Question 16

Locomotion of cniderias

Answer 16

• Some polyps are permanently attached (sessile)
• Hydra and sea anemones can move slowly by gliding on pedal disc
• Sea anemones occasionally swim
• Medusae can move freely by contracting the bell

Question 17

cnidocytes

Answer 17

Stinging cells in ALL cniderias

Question 18

T/F :Both cniderias and Ctenophores have cnidocytes

Answer 18

False! All cniderias but not all ctenophores have cnidocytes

Question 19

Nematocyst

Answer 19

most common type of cnidocyte
• Many nematocyst have a toxin which
paralyzes prey

Question 20

Cnidocil

Answer 20

• (modified cilium) triggers the nematocyst to fire

Question 21

Cnidocyte

Answer 21

• cell that holds cnida

Question 22

Class Hydrozoa characteristics

Answer 22

cnideria:

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

Question 23

Class Scyphozoa characteristics

Answer 23

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

Question 24

Class Cubozoa Characteristics

Answer 24

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

Question 25

Class Anthozoa Characteristics

Answer 25

cnideria
• 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 26

Phylum Ctneophora Characteristics

Answer 26

• Cell-Tissue level of biological organization (some organs may occur)
• Diploblastic
• Blind gut
• Approximately 150 species
• All marine, especially in warm waters
• Do not have nematocysts