 |
| Top: A nematocyst, before and after being discharged Bottom: Generalized cnidarian body plan |
_________________________________________________________________
Today we finished our discussion of porifera by talking about their reproduction, asexual (cellular regeneration, budding, through gemmules) and sexual (internal fertilization, with zygote developing into an amphiblastula or parenchymula larva).
We closed the chapter with a brief mention of the most accepted poriferan phylogeny.
We briefly discussed the phylum Placozoa, a phylum with one species as a representative, although there is some molecular evidence suggesting there could be several species.
Finally, we started our discussion on Cnidaria. We started with some of the general features of the phylum, in terms if diversity, habitat, and development. It is the first phylum we consider showing symmetry, in this case radial, and true tissues, derived from two embryological layers (diploblasts)
We discussed the general body plan, with an epidermis, a gastrodermis, and a mesoglea between the two, with the gastrodermis lining a gastrovascular cavity. We also discussed one of the defining characters of the phylum: the presence of cnidae, specialized organelles in cells called cnidocytes, with a variety of functions, but most prominently used for feeding and defense, in which case the specific cnida is called nematocyst.
Learn a little about sponge reproduction
-----------------------
No comments:
Post a Comment