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| A crustacean embryo (http://www.flickr.com/photos/artour_a/4174414482/) |
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Today we briefly mentioned the two types of life cycle that we will find in invertebrate phyla: Direct and indirect. Being indirect the most common case in the phyla that we'll cover in this course.
We discussed how developmental characters can be used to help inferring phylogenies and showed how, if looking early enough in the development of an organism, similarities across widely different metazoan phyla can be found. For instance, we talked about how the pattern of cell division after fertilization can determine two major groups of bilaterians: Protostomia and Deuterostomia.
We also started our discussion on the phylum porifera.
We talked about the basic body plan, how the choanocytes promote water movement so an entire individual can filter feed, and how non-specialized ameoboid cells, the archaeocytes can differentiate into the other cell types characteristic of this phylum (porocytes, pinacocytes, sclerocytes, choanocytes).
Next, we'll discuss the types oc canal systems found in sponges, which allow for the diversity of shapes that is found among the 7000+ (up to 15000) species of poriferans.
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| Basic body plan in Porifera and detail of a choanocyte and an amoebocyte |
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