Chapter 27 Flashcards
symmetry around a central axis
cnidarians and ctenophoras have this symmetry
radial symmetry
is able to divide into two equal parts
platyhelminthes
bilateral symmetry
embryo development
fertilization –> blastula –> gastrula
an animal embryo at the early stage of development when it is a hollow ball of cells
blastula
an embryo at the stage following the blastula, when it is a hollow cup-shaped structure having three layers of cells
gastrula
a layer of tissue on the outside of a mammalian blastula, supplying the embryo with nourishment and later forming the major part of the placenta
trophoblasts
fluid-filled cavity within the blastophore
blastocoel cavity
a pit in the side of the embryo, through which cells fated to be endodermal flow so that they leave the outer surface of the embryo and can create a new inner surface
blastopore
having a body derived from only two embryonic cell layers (ectoderm and endoderm, but no mesoderm)
diploblastic
having a body derived from three embryonic cell layers (ectoderm, mesoderm, and endoderm)
triploblast
is an invertebrate that does not have a coelom or body cavity, only cavity is the digestive cavity and it only has tissue, and ectoderm and an endoderm
ex: platyhelminthes (tapeworm, planarians, trematodes or flukes)
acoelomates
an organism with a “fake” body cavity, has an ectoderm, endoderm and mesoderm
ex: nematodes
pseudocoelumates
animals that have internal body cavities, or coeloms; ectoderm, endoderm and coelum
Ex: humans
true coelom or coelomates
function of coelom
space and protection
the ectoderm is…
skin and nervous system
