CNIDARIA Flashcards
Characteristics
- 2 true cell layers (either side of mesogleoa)
- no through gut
- armed with nematocysts ( in cells called cnidae, in arms or tentacles for feeding )
- radial symmetry
- nerve net but no brain
- 2 body forms: polyp and medusa, showing asexual and sexual characteristics
- colonial
4 subclasses of Cnidaria
1) Hydrozoa (hydroids)
2) Cubozoa (comb jellies)
3) Scyphozoa (jellyfish)
4) Anthozoa (anemones)
H.A.S.C
Cnidarian body plan
2 cellular layers: an endoderm (=gastroderm) and ectoderm (=epidermis) separated by an acellular Mesogloea
Cnidarian gastrovascular cavity function and structure
Function: -storage and digestion of food
- storage of gametes
- hydrostatic skeleton
- used for waste removal & gas dispersal
Structure: - divided internally by mesenteries
- Polyps have muscles to assist contraction
- GVC is filled by ciliary currents in the pharynx
1) Polyps reproduce sexually by….
Asexually by….
2) In jellyfish, the ______ form dominates.
3) Anthozoa only have _____.
4) Hydrozoan lifecycles
1) Producing/ releasing sperm/ eggs
budding
2) medusae
3) polyps
4) alternate between sexual medusae that are brooded in asexual polyps
- In some hydroids, the medusae are never free, and
dispersal is by small polyp-like larvae called actinulae
Benefits of sex
Cons of sex
1) genetic diversity opportunities/ shuffles genes
Cons: 2 fold cost of males halves growth rate
Benefits of asex
Costs of asex
Benefits: : All individuals female, no cost of males
• All genotypes identical: successful genotypes preserved,
Costs: no novelty.
If you can be either sexual or asexual, when
should you switch?
If resources available and competition low, be asexual and occupy the space as fast as possible with polyps. Limited to lifetime of habitat.
If resources scarce or competition intense, either get out
(sexual medusae) or produce new genotypes (sexual
medusae or polyps). Essential to long-term survival.
Describe coloniality in Cnidaria
_____ show very little colonial polymorphism
joined individuals linked by a shared GVC
formed via incomplete separation in asexual budding
individuals can be polymorphic
ANTHOZOA
_____ show division of labour among polyps. Example?
Hydrozoa, (Order: SIPHONOPHORA) the portuguese man ‘o war (Physalia physalis), is polyps-only.
1 polyp is modified as a float
Others are specialised for
feeding and reproduction
Photosynthetic symbionts are best known in corals using ______ zooxanthellae producing ____, essential for shallow water ecosystems
Symbiodinium
Mucous
Instead of a through gut, Cnidarians have a __ ___ ___.
gastro vascular cavity
In colonial Cnidaria, cells have a shared (a) and are genetically (b). Polymorphism in (c) allows division of (d), particularly in the class (e).
a) GVC
b) identical
c) polpys
d) labour
e) Hydrozoans
