Cnidaria Flashcards
What are the characteristics of the Cnidaria?
Mostly marine
Cells well differentiated to form tissues
Body wall two layered plus mesoglea
Single body cavity- the coelenteron
Mouth generally surrounded by tentacles
Two main structural types- the polyp and the medusa
Alternation of generations
Possess nematocysts
May be solitary or colonial
What classes of the cnidaria exist?
Class- Hydrozoa
Polyp stage ‘dominant’ in most species
Hydroids
Class- Scyphozoa
Medusoid stage ‘dominant’ in most species
Jellyfish
Class- Anthozoa
No medusoid stage
Sea anemones
What orders exist in the class hydrozoa?
Trachylina (no polypoid stage)
Hydroida (includes most hydrozoans, well developed polypoid stage)
Actinulida (tiny solitary polyps)
Siphonophora (colonial, includes polypoid and medusoid individuals)
Hydrocorallina (polypoid and colonial)
What is a defining characteristic of the order Trachylina?
No polypoid stage
What is the life cycle of Aglaura (a Trachylina)?
Alternates between asexual and sexual phases
Begins with planula larva that settles into a sessile polyp
Polyp reproduces asexually
Producing medusae
Medusae develop into a free swimming sexual phase and release gametes for external fertilization
How is the order Hydroida described?
Includes most hydrozoans, well developed polypoid stage
Vast majority colonial with an external skeleton- the perisarc
What is the life cycle of the Obelia (Hydroida)?
Alternates between sexual and asexual phases.
Sessile polyps asexually forming medusae
The medusae mature and release gametes for sexual reproduction
Fertilized eggs develop into larvae
What are some examples of the order Hydroida?
Athecate hydroids- skeletal covering does not surround hydranth (polyp does not sit in a cup) e.g. Clava
Thecate hydroids- Skeletal covering surrounds hydranth (polyp sits in a cup) e.g. obelia
What are most hydroids?
Most hydroids are thecate
What concept is commonly seen in the order hydroida?
Polymorphism
e.g. Hydractinia on hermit crab
What are the zooids seen in Hydractinia?
Gonozooid
Dactylozooid
Gastrozooid
Gonozooid
Dactylozooid
Gastrozooids
How is the order Actinulida described?
Tiny solitary polyps, interstitial inhabitants
e.g. Psammohydra, Halammohydra, Otohydra
How is the order Siphonophora described?
Colonial, pelagic, includes polypoid and medusoid individuals
e.g. Physalia physalis
Does polymorphism exist in the order Siphonophora?
Yes
Gasterozooid
Dacytlozooid
Gonozooid
How is the order Hydrocorallina described?
Polypoid and colonial with CaCo3 skeleton
Milleporina (fire coral)
What orders exist in the class Scyphozoa?
Order- Stauromedusae (sessile, attached by stalk)
Order- Cubomedusae (box jellyfish)
Order- Coronatae- (bell of medusa constricted by a groove, many deep sea jellyfish)
Order- Semaeostomae- (bowl or saucer shaped medusa with scalloped margins)
Order- Rhizostomae (bell of medusa lacks tentacles)
How is the order Stauromedusae described?
Sessile, attached by stalk
e.g. Haliclystus
What does the order Cubomedusae consist of?
Box jellyfish
e.g. Carybdea
How is the order Corontae described?
Bell of medusa constricted by a groove, many deep sea jellyfish
Periphylla
How is the order Semaeostomae described?
Bowl or saucer shaped medusa with scalloped margins
e.g. Chrysaora and Aurelia
What is the reproductive cycle of Aurelia?
Alternates between medusa and polyp stages
The medusa reproduces sexually, releasing gametes that form larvae
The larvae settle to form a sessile polyp which asexually reproduces and forms an adult medusae
How is the order Rhizostomae described?
Bell of medusa lacks tentacles, oral arms branched and folded
e.g. - Rhizostoma
- Casseopeia- shallow tropical lagoons, contains symbiotic algae and lies upside down on seabed absorbing sunlight
What are the sub-classes of the class Anthozoa?
Subclass- Octocorallia - Polyp with 8 pinnate tentacles, mostly colonial
Subclass- Zoantharia- Polyps with more than 8 tentacles which are rarely pinnate. Solitary or colonial
What orders exist in the subclass Octocorallia?
Order- Stolonifera
Order- Telestacea
Order- Alcyonacea
Order- Coenothecalia
Order- Gorgonacea
Order- Pennatulacea
How is the order Alcyonacea described?
Soft corals, rubbery coenenchymal mass, skeleton calcareous spicules
How is the order Gorgonacea described?
Gorgonian corals, upright plantlike growth, skeleton of horny organic material, include sea whips and sea fans
e.g. Swiftia
How is the order Pennatulacea?
Sea pens, fleshy, flattened or elongate body, or rachis, skeleton of calcareous spicules
Sea pens are mostly feather-like in shape but there are other variations
What orders exist in the subclass Zoantharia?
Order- Zoanthidea
Order- Actiniaria
Order- Scleractinia
Order- Corallimorpharia
Order- Ceriantharia
Order- Antipatharia
How are the order Zoanthidea?
Small anemones with single siphonoglyph, no skeleton, solitary or colonial
How are the order Actiniaria?
Sea anemones, solitary, no skeleton, mesenteries in hexamerous cycles, usually 2 siphonoglyphs
e.g Actinia- intraspecific aggression
How are the order Scleractinia described?
Stony corals, mostly colonial, external calcareous skeleton, sclerosepta in hexamerous cycles
Mostly colonial but some solitary
How are the order Corallimorpharia described?
Radially arranged tentacles, similar to true corals but lack skeleton
e.g. Corynactis
How are the order Ceriantharia described?
Burrowing anemones with elongate bodies living in tubes in sediment, single siphonoglyph
What are the phylum Ctenophora (comb jellies)?
Pelagic marine animals- Superficially similar to Schyphozoa jellyfish
How are the phylum Ctenophora similar to Scyphozoa?
Similarities:
- Radial symmetry
- Jelly-like mesoglea
- Transparency
- Nematocysts present in one species
What is the distinction between the phylum Ctenophora and the Scyphozoa?
8 rows of cilia running round body- used for swimming with oral end forward (Scyphozoans tend to swim aboral end forward)
