Cnidarians Flashcards
Unique characteristics of cnidarians
- Release complex intracellular organelles called cnidae or nematocyst
- Presence of larvae stage called planula
- Among simplest living animals with true tissues
- All members lossess tentacles surrounding the mouth
- Mouth is the only opening to the gut
Cnidarians
- habitat
- examples
- 99% marine, 0.2% freshwater (all aquatic)
- most live attached (sessile)
- manh live colonialy (coral colony)
- jellyfish, sea anemones, corals, sea fans, sea whips
What is more complex- cnidarians or sponges
Cnidarians
Though still simple
Symmetry of cnidarians
Radically
Body layers of cnidarians
Diploblastic (2 enbryonic layers of living tissue)
- epidermis
- gatrdodermis
Mesoglea is a nin living jelly-like layer between the elidermis and the hypodermis
Despite non living, the mesiglea may hold living cells from the embryonic ectoderm called_____
Amoebocytes
-coukd functioj in digestion, nutritien transport, repair abd defend agaisnt bacteria
Body forms of Cnidarians
- members exhibit polymorphism (2 kr more body forms)
1. Medusa (jellyfish): have unbrella shaped inverted mouth (facing down) often, thuck jelly-like layer in body wall as in jellyfish. Move by contractions of “bell”-free floating, pelagic planktonic
2. Polyp (hydroid): tubular body, ysually sessile/attached, mouth sureounded by tentacles - in most species, these body forms are present at different stages of lifecycle; while both occur at the same tine individually
Cnidae
Stinging thread
Unique organelle produced by cells called cnidoblasts (nematoblasts) and released with explosive force for defence, food collection, and locomotion
-may be specialized for attachement to surfaces, wrapping small objects, penetrating surfaces or secreting toxins made of proteins (highky toxic)
Cnidae release may be triggefed by
Osmotic oressure, chemical and tactile stimuli usually detected by group of specialized cilia (cnidocil)
Cnidarians have no gills or respirsti organelles so they…
Gaseous exchange via diffusion through exposed epidernak and gastrodernal surfaces
Cnidarians only have one opening that serves as both..
The mouth and anus
Digestive cavity leads to single opening
Gonad development of cnidarians
Occurs in the dugestive cavity and embryos released through the mouth
Cnidarian Feeding
Memebrs are mainily carnivorous, fee feed on phytoplanton (soft coral), few are symbiotic with unicellular photosynthetic algae in their tissues (endosymbionts)
-most have one or more rings of tentacles surrounding mouth armed with cnidocytes (stinging cells) for capturing prey
Cnidarians posess both ____ and ____
Nerves abd muscles
However lack CNS, nervous control invokves network of neurons (nerve cells) and their processes (nuerites)
Cnidarians lack ____ and ____ systems
Respiratory and excretory
Life span of cnidarians
Sea andmone can for 80+ years
Jellyfish up to 10
Cnidarian reproduction
Both asexual and sexual
Asexual: budding, fission (sea anamones)
Sexual: most are dioecious (separate sexes); geberaly sperm are shed in water
Alteration of generations in some soecues; polyp produces asexually abd medusae reproduxe sexully
-some can switch genders (males are scarce)
Larvae stage in marine cnidarians is comminly called a
Planula
Cnidarians are classifed into 2 subphyla
- Medusozoa
2. Anthozoa
The two subphyla are then broken into whicb classes
Mudosoza-
- Scyphozoa
- Cubozoa
- Hydrozoa
Anthozoa
- Hexacorallia
- Octociallia
Class scyphozoa
- inverted cup shaped cnidarians commonly known as jellyfishes
- over 200 species
- all madine
- large sized
General characteristics of scyphozoa
- mesoglea is thick gelatinous layer
- mouth us bourne through an opening called the manubrium
- Gastrovascular canal
- ability to process sensory info
- vertical migration in water
Scyphozoa gastrovascular canal
Fluid filled canal leading to the outside through the manubrium
-function in oxygen and carbon dioxide circulation and nutriebt distribution following digestion
Schyphozoa may form endosymbiotic relationships with
unicellular green algae (zooxanthallae) living inside the jellyfish
Sensory receptors of scyphozoa
Possess slighkt advanced sensory receptors with ability to process and integrate sensory signals:
- organ of balance (statocysts)
- simple light receptors (ocelli)
- some have touch receptors (sensory lappets)
Rholalia
Club-like structures housing the ocelli and staocyst, arranged around the swimming bell
Schphozoan reproduction
- separate sexes
- fusion of egg and sperm results in planula larvae (non feeding and attached)
- planula changes into a polypoid scyphistoma
- scyphiztoma grows and undergo budding asexually
- then strobilation: transverse division of the body into many modules (ashtrays) called ephrya
- ephrya develop to adult
Under unfavouravke lab condititions adult scyphozoans can…
Differentiate back to the ephryae
2 orders of scphozoans
- Semaeostomeae
- aurelia species (moon jellyfish) and cyanea (lion mane jellyfish); produces the largest known medusae - Rhizostomeae
- lack central mouth, but has many small oral openings leading jntk a complex canal system
- rhizostoma, cassiopea, stomolophus
Class cubozoa (cube like animals)
- body of memebrs are box like
- known as cubomedusa
- few members
Rhopalia of cubozoa
Compelx with lensed eyes
Decelops nervous systems with compelx eyes
Do cubozoans strobilate
No
Characteristics of cubozoa
- 4 tentacles or clusters of 4 around the edges of the bell, close to the 4 rhopalia
- giid swinmers
- body highly transparent
- 2cm dismter with 30cm tentacles
- tentacles are highky armed with toxic nematocysts called sea wasps
Habitat of cubozoans
Mainly tropical and subtropical waters with seasonal abundance
Food of cubozoans
Small fishes, crustaceans, annelids, but could kill animals larger than itself, even humand after injections with the toxins
-most venomous animal toxin (cubomedusae)
Class Hydrozoa (water animals) Characterisrics
- possess more polyp form than medusa
- gastroderm lacks nematocyst
- nematocyst only around epidermis
- smaller than scyphozoans (<2cm) and possess velum
- mesoglea lack cells
- mostly marine
- form symbiotic relationships with other hydrozoans and invertebrates like fish, sponges
Velum
Extended tissue which invaginates from the edge of the swimming bell to the manubrium
Hydrozoan reproduction
- fertilized eggs develop into planula larvae
- planula metamorphose into sessule polypoid form without statocysts and ocelli
- polyp form are typically more functionality and structurally complex than scyphozoan
- unique freshwater slecies (hydra) produce single and independnt polyp
- medusa form is absent
Some hydra soecies harvour symbiotic unicellular ____
Green algae (zoochloellae) in their tissues
Hydrozoan subclasses
- Hydriodolina (95%)
2. Trachylina (5-10%)
Hydriodolina
Mostly marine
Mainly Surface water dweller
3 orders of Hydriodolina
- Anthomedusae (sarsia, hydra, tubularia)- bell shaped free living medusa when present
- Leptomedusae (Obelia, clytia, sertularia): medusa not when present are flat, never bell shaped, 100% marine, may form assiciaition with molluscs, living in the mantle cavity of oysters, bivalves, and mussles
- Siphonophora (portugese man of war)- marine and contain nematocyst for killing prey that is toxic to humans
Subclass Tachylina
Marine abd pellagic (mainly in warm open water) ex: liriope species
Tachylina orders
- Narcomedusae
- Limnomedusae
- Trachymedusae
- Actunulida
Subphylum Anthozoa (flower animals) unique characteristics
- lack medusa form
- lack operculum and corals
- mDNA is circular like eykaryotes but unique in cnidarians
- possess ciliated groove (siphonoglyph) in the pharyngeal wall leading from the mouth.
- distinct sheets of tissue (septa) separate the coelenteron
Ex: sea anemines and corals
What is the most abundant group of cnidarians
Anthozoans (70%)
-15 orders and 6000 species
Anthozoan habitat
- all marine
- mostly colonial (corals)
- some live solitary (sea anemones)
Anthozoan members can secrete
Skeleton composed of calcium carbonate or protein
Anthozoan reproduction
Asexually vis transverse or longitudinal fission by pedal laceration; portioj of foot (pedal disc) breaks off from the adukt Nd differentiates into a new individual.
Subclasses of anthozoan
1. Zoantharia Common orders: -Actinaria -Corallinorpharia -Scleractinaria
- Alcyonaria
- Stolonifera
- Gorgonacea
- Pennatulacea
- Alcyonacea
Acontia
Located in gastrovascualr cavity of anemones (anthozoans), thread like tissue containing numerous stinging threads
Which mesentery of anthozoans have nematocysts?
Incompelte mesenteries to secrete digestive enzymes and cells that phagocytize bacteria
