Module 5

Question 1

Cnidaria

Answer 1

placed after sponges in the animal kingdom - this suggests they are similar in terms of anatomy
- restricted to aquatic environments
- mostly marine
- many organisms depend on them for food and shelter

Question 2

Characteristics of Cnidaria

Answer 2

radial or bilateral symmetry
- mostly radial
polyps and medusa body plans

Question 3

Polyps body plan

Answer 3

benthic and sessile
- largely exist attached to the seafloor
- sit with their tentacles and mouths up

Question 4

Medusae body plan

Answer 4

pelagic and free-swimming
- floating in and around water using water currents and waves

Question 5

Diploblastic

Answer 5

cnidarians are diploblastic - have two cell layers
- endoderm
- ectoderm
- these are seperated by the mesoglea

Question 6

Mesoglea

Answer 6

non-cellular jelly-like matrix in cnidarians that separates the endoderm and ectoderm
- serves as an internal skeleton
- aids with structural support and provides elastic properties

Question 7

Hydrostatic skeleton

Answer 7

contain no rigid bones
- maintained by the internal pressure of fluids within organisms
- provides structural rigidity
- muscle contractions create changes in hydrostatic pressure – allows animals to hold their shape without bones or solid skeletal structures

Question 8

Why is a hydrostatic skeleton beneficial in cnidarians?

Answer 8

the lack of rigidity in hydrostatic skeletons is beneficial for the functioning of their tentacles

Question 9

Cnidae

Answer 9

stinging cells
- nematocysts rest coiled inside cnidocyte cells in the mouth and tentacles of cnidarians
-when triggered, these are fired out in a cnidoblast
- water rapidly fills the cells to increase hydrostatic pressure and fire the cnidoblast
- chidas are shed after firing but rapidly regenerate
- can be used for attachment and locomotion on some species

Question 10

Simple nervous, digestive, and muscular system in cnidarians

Answer 10

cnidarians have true tissues, nervous and muscular systems
- nerve net: range of sensory neurons distributed around their bodies
- nervous system network in replacement of a cephalisation
- have a neuromuscular system with bi-directional signal transfer between sensory and muscular systems
rhophalia: sensory cells which host statocysts for balance and orientation and ocelli for photosensor reception
epitheliomuscular cells: run longitudinally and circularly around the body with contractions that result n movement and locomotion in any direction

Question 11

Cephalisation

Answer 11

concentration of cells forming the head or brain
- cnidarians do not have these but make up for it with a nervous system network/nerve nets

Question 12

Nerve net

Answer 12

range of sensory neurons distributed around the body

Question 13

Rhopalia

Answer 13

sensory cells
- statocysts: balance and orientation
- ocelli: photosensory

Question 14

Epitheliomuscular cells

Answer 14

run longitudinally and circularly around the body with contractions that result in movement and locomotion in any direction

Question 15

Cnidarians lack excretory, circulatory or respiratory systems

Answer 15

blind gut: oral and asborel end with one opening
gastrovascular cavity – differs for species

Question 16

Gastrovascular cavity

Answer 16

siphonoglyph: ciliated groove at the mouth and pharynx that helps to create in-current water flow
- assists in assessing prey
mesenteries and septa: body-wall extensions that create folds and surface area inside the gastrovascular cavity
- paired or unpaired
mesentrial filaments: long and thin digestive structures that can be expelled to help capture and reel in food
- used as an offensive weapon

Question 17

Four main classes of cnidaria

Answer 17

Anthozoa
Hydrozoa
Scyphozoa
Cubozoa

Question 18

Anthozoa

Answer 18

mostly benthic
- Hexacorallia
- Scleractinia
- Ceriantharia
- Octocorallia

Question 19

Hexacorallia

Answer 19

anthozoa
- anemones and corals
- both solitary and colonial forms
- have tentacles and mesenteries in multiples of six
- 0 to 2 siphonoglyphs
- tentacles are unbranched with polyps that are diverse in structure
- hard or soft skeletons

Question 20

Scleractinia

Answer 20

order with Hexacorallia - Anthozoa
- true hard corals
- secrete a calcium carbonate skeleton in colonies formed of tiny polyps that are identical clones
- have a symbiotic relationship with zooxanthellae
- tentacles in multiples of 6

Question 21

Ceriantharia

Answer 21

Anthozoa
- tube-dwelling anemones
- unpaired mesenteries and unpaired tentacles
- long outer tentacles are used for food capture and defence
- small inner tentacles are used for food manipulated and ingestion
- solitary animals that bury in soft sediment with their tentacles sticking out, waiting to capture foo

Question 22

Octocorallia

Answer 22

Anthozoa
- soft corals, including sea pens and sea fans
- more uniform in structure with 8 pinnate tentacles and mesenteries
- pinnate: tiny branches on each tentacle
- have a single siphonoglyph
- almost all are colonial

Question 23

Coral polyps

Answer 23

autotrophic or heterotrophic

Question 24

Hydrozoa

Answer 24

marine and freshwater ecosystems
solitary and colonial forms
polyp and medusae forms

Question 25

Polyp and medusae Hydrozoa

Answer 25

polyp:
- asexual
- locomotion occurs by crawling, swimming, and looping

medusae:
- sexual/adult form
- have a vellum: extensions of the jellyfish bell that aids in pulsation and locomotion

Question 26

Hydrozoa hybrid life-stage

Answer 26

individual hybrid polyps have specialised roles in a colony
- gastrozooids: specialised for feeding
- gonozooids: colonial hybrodozoans that are specialised for reproduction
– lack tentacles and contain numerous buds from which the medusoid stage of the life cycle is produced
- dactylozooids: defensive polyps armed with large numbers of stinging cells

Question 27

Blue bottle

Answer 27

Hydrozoa - colony of polyps
- float on the surface of water with their pneumatophore, a gas-filled polyp
- have tentacles with >1000 zooids per colony

Question 28

Scyphozoa

Answer 28

true or swimming cnidarians/jellyfish
- has no velum
- have 8 notches around the margin of the bell that hosts sensory organs
- can detect light and touch
- muscles used for locomotion through pulsation

Question 29

Cubozoa

Answer 29

medusae are the dominant form
- tentacles stem from the pedalium in each corner of the box-shaped bell
- have specialised sensory organs
– rophalia
– velariam for locomotion

Question 30

Reproduction in Anthozoa

Answer 30

asexual reproduction
- budding or cloning of polyps for identical replicates
- anemones can split themselves through fission and regenerate their fragmented bodies
- broadcast spawning

Question 31

Asexual reproduction

Answer 31

polyp budding occurs to generate the medusa form
- strobilation: clones from the asexual polyp bud off into a medusa
- these medusa buds are called ephyra develop into adult jellyfish that can reproduce sexually

Question 32

Regeneration

Answer 32

some species of cnidaria even have the ability to regenerate their dying medusa phase
- many polyps and medusae can regenerate after significant damage to their body parts
- hydra are regeneration superstars and can reaggregate themselves following the complete dissociation of cells