Clade Radiata Flashcards
Phylum Cnidaria?
Nettle like
Characterized by cnidocytes (contains specialized stinging organelles)
Mostly marine
Ancient group- longest fossil history of all metazoa
Traditionally 4 classes but 5th proposed
Class Radiata?
Sponges are asymmetrical and do not have true tissues
True tissues characterize the clade eumetazoa
Phylum Cnidaria and Ctenophora are basal members of clade eumetazoa
Exhibit radial symmetry and are diploblastic but only have tissue level organization (no organs)
Who are the Cnidaria?
Mostly in warm shallow marine habitats
Efficient predators
Sometimes symbiotic relationships
Many sessile but others can move slowly
Cnidarian form?
Many exhibit polymorphism
Polyp: sessile
Medusa: floating or free swimming
Both have similar structure
Body wall?
Surronds gastrovascular cavity
Outer epidermal layer, inner gastrodermal layer, mesogleal layer in between
Mesoglea?
Gelatinous jelly like
Can contain fibres, ameboid, epitheliomuscular cells
Gastrodermis?
Epithelial cells lining gastrovascular cavity
Can contain nutritive muscular, interstitial and gland cells as well as cnidocytes, gonads
Very weak muscle layer so water in cavity serves as hydrostatic skeleton
Epidermis?
Outer layer containing various cells
Epitheliomuscular?
Covering and contractions
Interstitial?
Undifferentiated stem cells
Gland?
Secrete mucus
Cnidocytes?
Contain cnidae, abundant on tentacles
Sensory?
Flagellum as receptor, join with nerve cells
Nerve?
Multi or bipolar
Cnidae?
Tiny capsules within cnidocytes
Capsules covered with operculum
Contain coiled thread
Has tiny barbs in most common form (nematocysts)
Why have cnidae?
3 diff functional types
Penetrants, volvents, glutinants
Penetrants?
Penetrate prey and inject venom
Volvents?
Recoil and entangle prey
Glutinants?
Secrete adhesive
How do cnidae work?
Most equipped with modified Cilium acting as a trigger (cnidocyl)
Others sensitive to vibrations
Discharge under enormous hydrostatic pressure
Nerve net?
No central nervous system
Diffuse nervous network comprised of two connected nerve nets
Can be considered a neural muscular system in conjugation with sensory and epitheliomuscular cells
Feeding and digestion?
Mouth opens into gastrovascular cavity
Gland cells secrete enzymes and initiate extracellular digestion
Nutritive muscular cells phagocytize particles
Undigested particles carried by ameboid cells back to gastrovascular cavity for expulsion
Locomotion for cnidaria?
Colonial polyps are permanently attached
Hydros and see anamones can glide via mucus secretions using pedal discs
Also measuring worm movement
Medusae swim by contracting the bell
Reproduction?
Polyps and medusae play diff roles
Polyps can make other polyps via asexual reproduction
Clones via budding or fission
Clones can be dispersed or can stay attached to form a colony that may exhibit division of labor
More on reproduction?
Polyps in classes Hydrozoa and Scyphozoa eventually make medusae asexually
Medusae are dioecious (male or female individuals)
Produce gametes and reproduce sexually to form a free swimming zygote larva (planula)
Polyps or medusae?
Sea anemones and corals are all polyps (both have sexual and asexual reproduction tho)
True jellyfish are only medusae
Hydrozoa can alternate forms
Class Hydrozoa?
Life cycle alternates bw polyp and medusae
Lack tentacles for feeding
Most are marine and colonial
Hydras are an exception
Feeding of Hydrozoa?
Feeding response cuz of glutathione
Released by prey, wounded by nematocysts
Usually asexual budding
Hydroids?
Typical members of class Hydrozoa Have a medusa stage in life cycle
More on Hydrozoa
Have base, stalk, and 1 or more terminal polyps (zooids)
Most polyps are feeding forms (hydranths or gastrozooids)
Some have forms for defence (dactylozooids)
Newly budded individuals do not detach but add to the colony
Medusae form?
From buds of gonangiae
Usually leave colony as free swimming larva (planula)
Hydroid medusae typically small
Class Scyphozoa?
Most of the larger jellyfishes ->predominately Medusas
Many are bioluminescent
No velum on bell but often have a scalloped margin
Gonads in gastric pouches->internal fertilization, ciliated planula larva attaches and develops into a scyphistoma to make more polyps or a strobila that becomes medusa
Class staurozoa?
Solitary stalked polyp
Polyp top resembles a medusa
Sexual reproduction
Class Cubozoa?
Predominant medusa
Bell shape, almost square with tentacles at each corner
Tentacle base as a tough blade (pedalium)
Rhopalia each have six eyes
Umbrella margin not scalloped and turns inwards to form the velarium (like a velum)
Deadliness of Cubozoa?
Most deadly cnidocytes to humans found in tropical seas
One member, the sea wasp (chironex fleckeri) is claimed to be most venomous marine animal known
Horribly painful
Most humans die after getting stung, specially if they are swimming
Lions mane: also painful+fatal stings. Toxins appear to be species specific.
Class Anthozoa?
Occur only as polyps Coral and sea anemones Found in diverse marine environments Solitary or colonial Many supported by skeleton Divided into three subclasses: zoantharia, octocorallia and who cares
Subclass zoantharia?
Sea anemones
Cylindrical with crown of tentacles surrounding an oral disc and pharynx
Cavity as 6 chambers
Aconite also contain nematocysts
Also contain zoantharian corals
Stony corals
Tiny anemones living in secreted calcareous cups
No pedal disc but skeletal cup~also hexamerous
Large sheet over time
Subclass octocorallia?
Soft and horned corals
Cavity as 8 chambers->8 feather like tentacles around oral disc
Almost all are colonial and communicate through gastrodermal tubes (solenia).
Very important ecosystems. Habitat and nursery for many fish
Reef building takes dissolved calcium and carbonate ions and precipitate it to form reefs.
Where cnidaria live?
Shallow waters
Warm waters
Clear waters with little or no nutrients (zooxanthelle need light for photosynthesis).
Phylum Ctenophora?
Comb jellies
8 rows of comb-like plates (ctenes) used for locomotion
Can bioluminese
Can have adhesive cells (colloblasts) but do not make nematocysts
Also predators like Cnidaria
All are monoecious
Ctenophora medusa or polyp?
Support for idea that anthozoan life was ancestral
Medusoid form added later
New grouping maybe (medusozoa?)
