Ctenophora Flashcards
All animals share embryonic morphology and development as determined by
Hox gene
Hox gene
master control genes
Hos genes code
protein transcription factors
determine animal body plan
These genes code protein transcription factors and ultimately determine animal body plan
Head/tail directionality, number of body segments, number/location of appendages, etc.
Hox genes are are homologous in all animals
(except Ctenophora and Porifera)
The order of hox genes determines
anterior/posterior axis, body segments, appendages
Hox genes have undergone 2-4 duplication events
The additional genes allow for more and more complex body types
Invertebrates
one set of Hox genes
Vertebrates
4 sets of hox genes
Ctenophora and Porifera do NOT have Hox genes
We will talk about how current research shows
Ctenophora are the most ancient of all animals
All other animal clades have at least one set of Hox
genes
and up to four sets
Some animals are diploblastic
they have 2 germ layers
asymmetrical and radial symmetrical animals
Diploblastic Ectoderms
germ layer covers surface of animal
diploblastic endoderm
germ layer forms wall of digestive tract
Some animals are triploblastic
Three germ layers
Bilateral symmetrical animals
Triploblastic Ectoderm
covers surface of animal
Triploblastic Endoderm
forms digestive tract, respiratory tract, urinary tract
triploblastic Mesoderm
forms muscle, bone, circulatory system, etc
A coelom
is an internal body cavity derived from mesoderm
tissue
* Provides cushioning to internal organs
* Allows for body flexibility
Triploblasts that do NOT have a coelom are called
acoelomates
acoelomates
Their mesoderm region is completely filled with tissue
Example: Platyhelminthes (flatworms)
Triploblasts that have a coelom that is completely surrounded
by mesoderm tissue are called
eucoelomates
eucoelomates
Example: echinoderms (starfish) and chordates (animals with a
backbone)
Triploblasts that have a coelom that is lined partly with
mesoderm and partly with endoderm are called
pseudo-coelomates
pseudo-coelomates
Example: Nematoda (roundworms)
Bilaterally symmetrical, eucoelomates can be further divided based on the
origin of
their mouth/anus
The archenteron
is the beginning of the gut
the opening
is called the blastopore.
The archenteron extends through the blastula
to create another opening.
The opening on one end will become the mouth, the opening on the other end will become the
anus.
In Protostomes, the blastopore becomes the mouth
- This is more primitive
- Arthropods, mollusks, annelids
- Platyhelminthes is a protostome but only has one opening
In Deuterostomes, the blastopore becomes the anus
- This is a novel, autapomorphic trait
- Chordates and even echinoderms
Phylum
Ctenophora
Commonly called Comb Jellies
* Not related to true jellyfish
* Over 100 known species, all marine
Ctenophora Phylogeny
- Thought to be related to Cnidarians
- This put Porifera as the basal group of all animals
*No Hox genes
Just published research shows that Ctenophora
are actually the most
ancient of all animals
Compared genomes of ctenophores, sponges, and two-celled animals
sponges, the two-celled animals, and all other animal phyla exhibit a specific
chromosomal fusion and rearrangement
basal group
Ctenophores
Ctenophora Superficially resemble medusa forms of Cnidaria
Morphologically, very different
Morphology
- They have no stinging cells
- They exhibit biradial symmetry
- They are triploblastic protostomes
- Mesoderm forms network of muscles
- Their mesoderm is endodermal in origin (???) and it all becomes muscle
Ctenophora Movement is produced by
cilia fused into their ctenes (comb plates)
Most have 8 ctenes distributed around their body
Ctenophora hunting
active hunters with adhesive cells on their retractable
tentacles
Their digestive “system” is unique
Prey enters mouth, travels to pharynx then gut where it is digested by enzymes
* Solid food waste is then ejected back out of the mouth
* What type of digestive system is this?
They have anal pores…why?
Metabolic waste
They have sophisticated
epithelial sensory cells with light receptors,
mechanoreceptors, and gravi-receptors
- Most are bioluminescent
The nervous system is organized into
an epithelial
nerve net and a mesogleal nerve net. There are two
parallel nerves that extend into the tentacles.
They are monoecious animals
Both male and female gonads
They release both eggs and sperm into the water at the same
time
- This is sometimes spontaneous and sometimes caused by the presence
of other Ctenophores nearby - Can self-fertilize or reproduce with other Ctenophores
