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 Porifera - the sponges
This phylum's 'place'
relative to other phyla:
Selected taxa within this taxon:

  Porifera are typically marine, sessile animals with a most unusual body that is porous.

This is our first group of Metazoans (=animals) - Criteria based on:

Molecular data supports a monophyletic origin of metazoans.

Phylum Porifera: The Sponges
'Pore-bearing' animals.

Diverse: ~5,000 living species described.

Sponges have 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 
associations from 
Doushantuo phosphorites 
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)

Body Plan

Micro-suspension feeders as opposed to macrophagy in most other animals

A variety of growth form that can be loosely assigned into various body types:  

  Are they unsuccessful organisms?

Natural History

Some are symbiotic with alga, and one small group is considered carnivorous .
No recorded extinctions of modern species, but threatened particularly by sedimentation  (why?) and destruction of their habitat.


Major classes of modern sponges
Class Hexactinellida - glass sponges

Siliceous spicules  (six intersecting rays) with secondary network of cells forming trabecular net.   Live at very great depths and osculum is notably large.  Why?
Class Demospongia

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

Class Calcarea

Spicules of calcium carbonate and may be straight or composed of 3-4 rays.

Other classes:
"While I pass with my spongiological work the columns of Hercules, I am facing a task which, to
its full extent, can only be performed with the strength of a hero."
O.E. Schmidt 1870, second chapter, preface
  Recent techniques in phylogeny help to establish at the sponge body plan is basal for animals.  Simple is truly primitive in this case.  Is this always true?

Lecture Sources:
  • Pechenik. Jan A.  2000. Biology of the Invertebrates.  McGraw-Hill, New York.

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