Chapter 4 - Cnidaria Flashcards
What are non-reef-building corals called?
Ahermatypes/ahermatypic coral
This is contrasted with reef-building coral which are hermatypes/hermatypic coral
Name the most common types of cnidocytes.
- Penetrant
- Volvent
- Glutinant
This type of cnidocyte captures prey with an elastric thread by entaglement
Volvent
This type of cnidocyte secretes adhesive mucus for locomotion and attachment
Glutinant
This type of cnidocyte penetrates prey and injects poison
Penetrant
What are nematocysts?
A specialized stinging organelle which penetrates prey and injects a paralyzing toxin
How many species are in phylum Cnidaria?
Over 9,000
Name the classes of Cnidaria (including the most recent)
Hydrozoa, Scyphozoa, Cubozoa, Anthozoa, Staurozoa
What do the Hydrozoans include?
Hydroids, fire corals, colonial siphonophores like Portuguese man o’ war
What do the Scyphozoans include?
True jellyfish
What do the Cubozoans include?
Cube or box jellyfishes
What do the Anthozoans include?
Stony and soft corals, sea anemones
What are the Staurozoans?
Cnidarians with no medusae in their life cycle, but have their polyp topped by a medusa-like region
What are the shared features of both polyp and medusa forms?
They both retain sac-like body plans
Polyp (hydroid) forms are…
adapted to sedentary or sessile lifestyle
Medusa (jellyfish/sea jelly) forms are…
adapted to free-living and floating existence
Describe the polyp form
- Tubular body with the mouth directed upward and surrounded by tentacles
- Mouth leads into a blind gastrovascular cavity
- Two ends, oral and aboral end
- Aboral end is attached to substratum, by pedal disc
- Reproduces asexually by budding, fission, pedal laceration
Describe the medusa form
- Bell- or umbrella-shaped and exhibit tetramerous symmetry
(arranged in fours) - Usually free-swimming or free-floating
- Tentacles may extend down from the rim of the umbrella
- Medusae equipped with statocysts (orientation) and ocelli (light sensors)
What type of symmetry do medusa forms exhibit?
Tetramerous symmetry
How does the aboral end of polypoids stay attached to the substratum?
Pedal disc
What helps medusae stay oriented?
Statocysts
These are light sensors in medusae
Ocelli
How do hydromedusae differ from scyphomedusae?
Hydromedusae have the presence of velum (shelf-like fold of tissue from the bottom of the bell that extends into the bell)
What are the larvae of cnidarians called?
Planula larva
What do the planula larvae develop from?
The zygote of the cnidarian
Describe the life cycle of cnidarians
- Zygote develops into a motile planula larva
- Planula settles on a substrate
- Metamorphoses into a polyp which produces other polyps asexually
- The polyps produce a free-swimming medusa by budding
- Medusa then reproduce sexually and form a zygote
What are the class of true jellyfish?
Class Scyphozoa
True or False: Medusae are monoecious and can reproduce asexually
False, they are dioecious and reproduce sexually
True or False: Scyphozoans have both attached and free-swimming stages that occupy pelagic and benthic environments
True
Describe the scyphomedusae
Large and conspicuous; larger than hydromedusae; lack velum; have extended mouth edge called manubrium with four frilly oral arms or lobes that are used in capturing and ingesting prey
What is the capsule of the nematocyst covered by?
Operculum
Where are the cnidocytes located?
Invaginations of ectodermal cells (and some endodermal cells)
What are the polyps of Scyphozoans generally?
Typically very small
What are the polyps and medusae of colonial hydrozoans usually like?
Polyps form colonies and medusae are pelagic (except for Hydra which have freshwater polyps)
True or False: Polyps are carnivorous but can also filter feed
False, they are purely carnivorous
Describe the process of digestion in polyps
Gland cells discharge enzymes to begin extracellular digestion
Describe Hydrozoans
Mostly marine and colonial, typical hydroid has a base, a stalk, and one or more terminal zooids
What are zooids?
Individual polyp animals that make up the part of a colonial cnidarian
Describe the epithelial layers of cnidarians
Epidermis - contains the cnidocytes, sensory cells, and nerve cells
Mesoglea - extracellular matrix between epidermis and gastrodermis, acts as hydrostatic skeleton
Gastrodermis - holds the gland cells which secrete enzymes
What is the scientific name of Portuguese man o’ war?
Physalia sp.
Name the two orders of Hydrozoa that contain species that form polymorphic swimming or floating colonies
Siphonophora and Chondrophora
