Introduction
    This week we will be looking at the Phylum Porifera, which includes several major classes of sponges, as well as the Archaeocyathids and Stromatoporoids (two problematic groups that have  found a home in the Porifera Phylum).  All three groups are quite ancient, with records that reach back to the early Cambrian.  They differ, however, in that the Archaeocyathids became extinct by the end of the Cambrian with their greatest diversity in rocks of Early to Mid Cambrian age, and the Stromatoporoids became extinct during the Cretaceous, although their most diverse period as reef builders was during Paleozoic time (Ordovician - Mississippian), and their probable descendents are still around, a Sponge Class called the Sclerospongea.
    The Sponges are still with us today as a very successful group.  Sponges are present in the Burgess Shale (Middle Cambrian time) and in Lower Cambrian rocks.  Cryptic sponge-like impressions have also been found in late Precambrian fossiliferous deposits.  In the Palaeozoic, sponges were often the main reef builders, alternating or sharing that position with corals.  Often, we find spicules that represent the skeletal remains of sponges.   Living sponges today are grouped into four major classes:  Hexactinella, Demospongia, Calcarea, and Sclerospongea, based on their cell wall structure and spicule composition.  In the fossil record, these groups are often represented by the spicules alone, which may be preserved  in great abundance, or by masses of fossilized sponges associated with reefs.
 
 
 
 
 

  Phylum Porifera (Cambrian-Recent) (see video, approximately 10 minutes, on biology of sponges)

Basic Facts & Terms to Know about Porifera:  They are:
1.	Eukaryotes
2.	Loosely organized Metazoans with a cellular level of organization (no organs)
3.	Limited in cell Specialization:  Some cells (Archaeocytes & Choanocytes) perform multiple tasks
4.	Asymmetrical or Radial in symmetry
5.	free-swimming in larval stage:  sessile (attached)as adults
6.	known to have Three Wall Types:  Ascon (simplest), Sycon and Leucon in order of increasing complexity (infolding, canals, and indentations)
7.	structurally supported by tiny spicules composed of silica or calcium carbonate.
8.	found in marine to freshwater habitats Sessile (Attached)or Encrusting and can be Reef Builders.
9.	Many (especially in shallow water) have symbiotic blue-green algae partners or harbor a variety of nemotodes, crustaceans and mollusks in the central chamber (osculum)

What ecological factors can you expect to be important to their survival?  Consider the problems of substrate type, respiration, feeding, and avoiding predation.

Consider the Following Questions as You Examine the Fossil Sponges in Lab:
1.  How can you know that this is a fossil sponge (or archaeocyathid, or stromatoporoid)?

2.  Can you see any useful details with your handlens?

3.  With what kind of marine environment do you think this fossil associated?

Class Hexactinellida:  The Glass Sponges  Precambrian; Lower Cambrian to Recent
Spicules are composed of silica, with ends or "axons"  set off at 90 ° angles.  Paleozoic forms lived in shallow marine water where many were reef builders, but in Mid-Mesozoic time shifted to deep ocean.  (Consider:  why?)  They are considered an early branch of the Porifera, because of their many differences from the other classes.  Consider This:  Why are silica spicules stable and well preserved in cold, deep ocean conditions?

Look at lab specimens of
Genus Hydnoceras
Range:  Devonian-Mississippian:
Hydnoceras was a reef builder during the late Devonian.   This is an index or guide  fossil for the Late Devonian.  These are probably internal molds of the sponge itself.

Image Shown with Permission from the University of California Museum of Paleontology at Berkeley
                                                           Hydnoceras
 
 

Class Demospongia:  Range:  Cambrian to Recent, Greatest diversity in Cretaceous time.
This class represents the most abundant and diverse group of sponges living today. Spicules are organic or made of silica, with axons of spicules NOT at 90° .   Demosponges can be found in shallow through deep marine settings, in freshwater (all freshwater sponges are demosponges).

Look at lab specimens of
Genus Astylospongia
Range:  Silurian
Astylospongia is an Index or Guide Fossil for the Silurian.

Image Shown with Permission from the University of California Museum of Paleontology at Berkeley

                                                       Astylospongia
 

Class Calcarea:  Range:  Cambrian to Recent, greatest diversity during Cretaceous.
Calcisponges may have spicules made of CaCO3 that come in unusual shapes, including stars and tuning forks, or they may have no spicules, but instead a calcareous framework..  Living calcisponges prefer shallow tropical waters (Think...what is the link between CaCO3 spicules and warm, shallow tropical waters?)

Genus Wewokella
Image Shown with Permission from the University of California Museum of Paleontology at Berkeley
 
 

Be Sure to see two calcisponge Guide Fossils in the Lab Collection...

Astreospongia (Silurian) (Look at the spicule sample under the microscope, too)

Girtyocoelia (Upper Pennsylvanian-Triassic)  These tiny bead-like calcisponges were important reef builders in late Pennsylvanian & Permian time).

 

Class Sclerospongia :  Range:  Recent, but may be linked to the extinct Stromatoporoids (Cambrian-Cretaceous).
Stromatoporoids  were massive calcareous reef builders of the Paleozoic, and have many characteristics in common with Sclerospongia.  In cross section, they show a pattern of horizontal layers with tiny vertical columns, and on the surface,  bumps and a star shaped canal system.

Look at the Stromatoporoid in the Lab
Would you be able to recognize this as a fossil in the field?
 

Cross-Section Image Shown with Permission from the University of California Museum of Paleontology at Berkeley

Stromatoporoid
 

Class Archaeocyatha  Range:  Early to Middle Cambrian, greatest diversity in Mid-Cambrian time
These simple, sponge like organisms were the great reef builders of Early and Mid Cambrian time.  Generally, they are small (see photo below) and cone shaped, with a simple double walled conical structure and wide circular opening at the top.  Separating the two walls were vertical plates called septa, both walls and septa were peforated with tiny holes.  As reef builders, they occupied shallow marine carbonate shelves, and may have had symbiotic algae, since they are typically associated with fossilized algae.  They are important Guide or Index fossils for the Early-Mid Cambrian.

Look at the Archaeocyathid in the Lab

Image Shown with Permission from the University of California Museum of Paleontology at Berkeley
http://www.ucmp.berkeley.edu/porifera/images/archaeocrack.jpeg

Part II.  Group Assignment:  Understanding Thermohaline Circulation  20 points.

Interested in what can be done with fossilized sponges?  Want to know more?  Here are some recent papers on the subject...
 
 

de la Rocha, Christina L., 2003.  Silicon isotope fractionation by marine sponges and the reconstruction of the silicon isotope composition of ancient deep water; Geology , v. 31 issue 5, p. 423-426.

Samankassou, Elias.2002.  Cool-water carbonates in a paleoequatorial shallow-water environment; the paradox of the Auernig cyclic sediments (Upper Pennsylvanian, Carnic Alps, Austria-Italy) and its implications. Geology , v. 30 issue 7, p. 655-658.

Wood, Rachel A., 1990.  Reef-building sponges; American Scientist, v. 78 issue 3, p. 224-235.

Wood, Rachel A., Debrenne, Francoise, Zhuravlev, Andrey Yu, 1992.  Functional biology and ecology of Archaeocyatha; Palaios, v. 7 issue 2, p. 131-156.