lec 5 Flashcards
animals belong in a clade called______, what else does it include
Opisthokonta, includes fungi and some protists
why is opisthikonta named that
prosteriorly placed flagellum
5 not unique features to kingdom animalia
- multicellularity
2.lack cell walls - are chemoheterotrophic
- mostly sexual
- are animate- can move
unique characteristics of metazoans
(5)
- gastrulation and embryonic tissue layering
- unique types of intercellular junctions
- type IV collagen
- striated myofibrils and actin-myosin contractile elements
- HOX GENES)
anisogamy
small motile sperm, large nonmotile eggs
do animals share similar patterns of fertilization and early embryonic development? describe it
most of them do share similar patterns.
1. diploid zygote initially undergoes a number of mitotic
cell divisions without growth of cells between divisions
2. eventually a ball of cells is formed
3. blastula invaginates at one end in many taxa, forms gastrula
4.gastrula has two clear layers of cells
direct development
embryo
gradually develops towards adult form
without sudden changes in morphology
indirect development
involves one or
more intermediate stages whose morphology and behaviour
differs greatly from sexually mature adult
stage
what are intermediate stages in indirect development called?
each called a
larva
intercellular junctions
specialized areas of contact
between plasma membranes of adjacent epithelial cells
Epithelia
tissues in which the component cells have an
aligned polarity, and are joined by intercellular juncltions, associate w extracellular matrix. to BASAL LAMINA
three main functions of intercellular
junctions in metazoans
- BARRIER- concentration gradients
- ADHESIONcell-cell or cell-substrate adhesion
- COMMUNICATIONallowing intercellular communication
collagen IV
-rope-like molecules
called collagen, glue b/w cells and let them collaborate.
-synapomorphy of metazoa (some sponges lost it tho)
basal lamina
thin layer of extracellular matrix that is
secreted by the epithelial cells and on which the living cells
of the epithelium
striated myofibrils
and actin-myosin
contractile elements
-allow for movement in some parts of body.
-some myosin types
appear to be ancestral to the Metazoa
homeobox
regulatory genes that produce proteins
that can turn other genes on and off
homeobox genes that control anterior
to posterior developmental sequence
of embryo
Hox genes
where are hox genes absent
absent in sponges, placozoans and ctenophores
the Metazoa groupis
monophyletic
when did animals arise
prior to Cambrian Explosion
where do hypotheses w metazoan evolution and lineage come from
on early embryo morphology and
hypothetical ancestral forms
Haeckel’s
gastraea
hypothesis
-a version of colonial theory
-the transition to
a multicellular condition occurred by invagination, a developmental process that
resulted in a hollow “gastraea.”
the two colonial theories branched from the theory of the
hypothetical colonial flagellate
ancestor
Metschnikoff’s “planuloid”
hypothesis
-the first metazoan was solid and developed by ingression of cells
- similar to cnidarian planula larvae
Bütschli’s “plakula
metazoans that arose after sponges had flattened disc-shaped
bodies with 2 layers of flagellated cells
Placozoans support this
what supports butschlis theory
discovery of placozoans
what supports phylum placozoa
cross striated cilary rootlets
Trichoplax adhaerens
-was the only species in placozoa until recently
-resembles Butschlis plankula hypothesis
placozoa features
- lack basal lamina
- shiny spheres of possibly repellant chemicals present in flattened and monociliate upper layer
how do placozoa move
cilary gliding along flat surfaces or swimming for v small mfs
reproduction in placozoa
fission
budding off small flagellated swarmers
diet of placozoa and digestion
-likely includes algae
-external digestion
what is placozoa+ proifera called?
what about remaining amimals?
parazoa
eumetazoa
Hox genes
homeobox genes control anterior
to posterior developmental sequence
of embryo
main constituent of the basal lamina
Collagen
main constituent of the basal lamina
Collagen
