lec 10 Flashcards
except for
Xenacoelomorpha,
the Bilateria is
divided into two
large clades:
Deuterostomia
and Protostomia
all bilateria except xenacoelomorpha
what supports this?
Nephrozoa
unique family of hox genes
what differs b/w protostome and deuterostome
1) origins of mouth and anus
2) origin of eucoelom
3)cleavage
4) # cilia
how do origins of mouth and anus differ? dogma
blastospore gives rise to:
mouth in Protostomia
-the anus arises secondarily
anus in Deuterostomia
-the mouth arises
secondarily
origin of eucoelom differing how?
Protostomia: solid mesoderm ‘splits’ to form schizocoely
Deuterostomia: pockets from embryonic gut cavity close
off and form enterocoely
schizocoely
mesodermally
lined coelom
enterocoely
enclosed, mesodermally lined coelom
how does cleavage differ? dogma
Protostomia it is spiral and determinate
Deuterostomia: cleavage is radial and
indeterminate
how does number of cilia differ? dogma
multiciliated cells in Protostomia
monociliated cells in Deuterostomia
truth abt mouth origin
-Deuterostomia do follow the
‘mouth second
-only some protostomia are mouth first
truth abt ciliation
monociliation is common in deuterostomes and rare in protostomes there are still exceptions
Protostomia
dorsal cerebral
ganglia form circumesophageal
connectives to ventral nerve cords
clade spiralia
-Lophotrochozoa
-many, but not all show spiral cleavage
-
spiral cleavage
-the first cleavages produce cells
slightly offset
-determinate cleavage–> each cell has predefined fate
-no identical twins
indeterminate
cell specialization
happens much later, and early twinning is possible
Phylum Platyhelminthes
considered basal
among the protostomes
30,000 spp
flattened in form
what protostome features do they lack
-no coelom or circ system
-blind gut–> no anus
-simple ladder like nervous system w anterior brain
what does platyhelminths nervous system lack
circumoesophageal connectives
features common to most flatworms
1 active excretion by network of protonephridia
2. tremendous capacity for regeneration &
asexual reproduction
3. hermaphroditic with internal fertilization
4. development is direct, without distinct larval stage
5. ectolecithal
ectolecithal
yolk is
on the outside of the fertilized egg
neoöphoran
-the yolk can go around a single
fertilized egg that is then surrounded
by an egg capsule
-several eggs can be surrounded by
yolk in a single capsule
entirely parasitic platyhelminth groups, monophyletic?
what are the rest placed in? monophyletic?
Trematoda, Monogenea Cestoda- probably monophyletic
the rest placed in class Class Turbellaria
paraphyletic
