Fall 2012 Lecture 28. Cnidaria and Ctenophora •Cnidaria basic features biology within-group diversity Ctenophora: brief introduction Students should be able to: explain the term diploblastand its relevance for phylogeny describe the unique cell type in cnidarians explain how this cell functions explain the explain the body plan of a cnidarian polyp explain the body plan of a cnidarian medusa analyze the cnidarian life cycle and the role of asexual reproduction distinguish cnidarians from ctenophores explain what is unusual about ctenophore locomotion
Transcript
Fall 2012
Lecture 28. Cnidaria and Ctenophora •!Cnidaria basic features
biology within-group diversity
Ctenophora: brief introduction Students should be able to: explain the term diploblast and its relevance for phylogeny describe the unique cell type in cnidarians explain how this cell functions explain the explain the body plan of a cnidarian polyp explain the body plan of a cnidarian medusa analyze the cnidarian life cycle and the role of asexual reproduction distinguish cnidarians from ctenophores explain what is unusual about ctenophore locomotion
Organization of animal body plans Symmetry: an animal is symmetrical if at least one plane can divide it into two similar, mirror-image halves
Radial symmetry: animal in form of cylinder, parts arranged around the long axis, and with multiple imaginary planes that divide the animal into equal halves
Bilateral symmetry: a single plane divides animal into left and right mirror-image halves
•! radial symmetry, around a longitudinal axis with oral (open) and aboral ends •! often with tentacles around the oral end
Quan
Sticky Note
oral end: mouth side aboral end: away from mouth side
Cnidarian diversity •! about 11,000 species four major clades of Cnidaria: Anthozoa (sea anemones, corals, sea pens) Hydrozoa (hydrozoans) Scyphozoa (sea jellies) Cubozoa (cube or box jellies)
Figs 31.19 and 20 8th ed
Cnidarians are diploblastic animals
Polyp
with
blind
gut
becomes adult gastrodermis
becomes adult epidermis
Feeding in Cnidaria Cnidarians are all carnivorous. Small animal prey captured with cnida-laden tentacles and conveyed into the gastrovascular cavity. Extracellular digestion occurs here. Products are taken by phagocytosis into nutritive cells (of the gastrodermis) where digestion is completed intracellularly.
They cover the tentacles and sometimes occur in the gut; they are used in defense and prey capture. Fig. 31.9 9th ed
Cnidocytes characterize
phylum Cnidaria.
Quan
Sticky Note
cnidocytes are stinging cells that cointain a coiled thread-like stinger structure called nematocyst. Nematocyst are shot out of the cnidocytes upon contact with prey.
Various polyp forms and a medusa form = one genotype
Quan
Sticky Note
ECM like mesohyl and mesoglea are not living tissue thus they do not need O2, O2 can only diffuse thru short distance thus only the outer living cells can acquire O2 and the thicker ECM (mesohyl and mesoglea) don't need O2. It fills the space that cannot be filled by living tissue because O2 cannot diffuse there.
Asexual reproduction: budding and fission
Clones
buds detach
Colony Budding
Fission
buds stay attached
Polyp
Colonies have a shared gut cavity
•! This permits food sharing which makes specialization possible.
•! Specialization occurs when some polyps feed (gastrozooids), others reproduce (gonozooids) and others specialize in defense (dactylozooids).
Multiple polyp forms—one genotype
Medusae are made asexually by a variety of methods soon to be described
They are made asexually, but their function is to reproduce sexually.
Quan
Sticky Note
frilly mouth lobes contains stinging cells
How do we fit all this into one life cycle?
It depends on the class.
Class Hydrozoa
see text figure 31.21 8th ed
See Figure 31.22 9th ed
Curves nature throws at us:
•! Sometimes the colony is not sessile, instead the whole colony floats around the ocean.
•! Sometimes medusae are not released, instead they stay on the colony.
•! Sometimes there is no medusa, just gonads on the body.
Fitting all the stages in Class Scyphozoa
Strobilation
see
http://vimeo.com/8247281
Figure 31.18 8th ed
Class Anthozoa
polyps only
no medusae
polyps may clone; they also make gametes
Polyp clones may fight for space on a hard surface
Curves nature throws at us
Corals contain symbiotic dinoflagellates called zooxanthellae; they leak carbon
products to the coral
symbiotic photosynthetic members of clade_____?____
Class Cubozoa cube or box jellies (sea wasps) •! small group •! sting very toxic some cube jellies have eyes with epidermal cornea, cellular lens, and multi-layered retina!
Cubozoa •! box jellies (sea wasps) •! sting very toxic •! some beaches in Australia closed for 6-7 months a year because of box jellies
Jellyfish stings are a serious problem. >2000 nematocysts will penetrate one square millimetre of human skin during contact with a jellyfish tentacle
Cnidarian postscript: what we have learned from Nemo
From web site of a skin products company (http://www.godivaskincare.com/store/pages.php?pageid=13): !"#$#%&'()*+,#-$)#.&$/#,0123$)13+224#5),$6721#8/#7$60)2#+9):26+;#(,/#-$)<=#+(07726+>#%&'()*+,#,$?2#$#.6'=2-9?2#-'$9):#=,$=#)25=6$&0@2+#=,2#*60):#72-,$)0+7#0)#=,2#+9):0):#-2&&+A#BC26#=2)#/2$6+#'"#2D=2)+0?2#80'=2-,)'&':0-$>+2$6-,#8/#!+6$2&0#+-02)9+=+;#0=#0+#)'(#.'++08&2#='#.6'=2-=#/'56+2&"#$:$0)+=#=,2#+9):+#'"#7'+=#E2&&/*+,;#E2&&/*+,#&$6?$2;#-'6$&#$)1#+2$#$)27')2A#!"#$%&'(&)*'(*&'-')=$0)+#=,2#+$72#8&2)1#'"#0):62102)=+#=,$=#-'$=#=,2#%&'()*+,F##Amit Lotan (the researcher involved) began his work at UC Davis. #
Ctenophores (comb jellies) – enigmatic group of uncertain position
•! radial symmetry •! diploblastic development •! complete gut
Very unusual because the body is propelled by cilia in rows called ctenes or comb rows.
