|Porifera - the sponges|
|This phylum's 'place'
relative to other phyla:
|Selected taxa within this taxon:|
This is our first group of Metazoans (=animals) - Criteria based on:
Phylum Porifera: The
Diverse: ~5,000 living species
typically been considered an early branching event in the
history of animals and may represent the ancestral body plan
of all animals:
1) Fossil sponges are among the oldest known animal fossils, dating from the Late Precambrian.
Simple cell and spicule
of southern China
(~570 million years ago)
Archaeocyaths are an extinct group
(~530 million years ago) and contributed
greatly to the creation of the first reefs.
2) molecular evidence: more closely related to other metazoans than any other living group, but other phyla are more closely related to one another than to poriferans.
3) genetic/developmental evidence: Would you expect sponges to have Hox genes? If they did, what would this suggest about whether the poriferan body is primitive?
4) The porifera may be a paraphyletic group with some taxa of sponges being more closely related to the other animal phyla than to other porifera taxa.
What does this paraphyletic relationship suggests about the body plan of the ancestor of all animal phyla?
5) Body plan unique and simple among animals (see below)
Aristotle classified sponges as plants.
What is being accomplished by this movement of water through the sponge?
Environmental conditions can
partially influence sponge morphology.
Sponges also provide a haven for a variety of parasites or commensals.
Some sponges bore
into the shells of bivalves, gastropods, and corals,
while others contribute to reef building.
Some are symbiotic with alga, and one small group is considered carnivorous .
Undergoes metamorphosis when
attaching to a substrate (external flagellated cells migrate
inward to become choanocytes).
Class Hexactinellida - glass spongesClass Demospongia
Siliceous spicules (six intersecting rays) with secondary network of cells forming trabecular net. Live at very great depths and osculum is notably large. Why?
Most diverse sponge group.
Spicules are of spongin (a collagen) and/or silicaeous, and includes 'bath sponges'
Variety of growth forms from encrusting sheets to branching stalks upright.
Commercial sponge harvest
Spicules of calcium carbonate and may be straight or composed of 3-4 rays.
Hexactinellids were widely viewed as an early branch within the Porifera, however there is controversy on the systematics of sponges based on recent molecular data.
Ideas to consider from the sponges: