are the simplest animals. Sponges do not have tissues or
organs. However, the cells that make up a sponge are integrated
and organized to filter feed, dispose waste, reproduce
and secrete a shared porous skeleton. As the simplest form
multi-cellular life, sponges possess the property of cell
recognition. A fine mesh can be used to separate sponge
cells individually after which, they will recombine to
form a new sponge. Sponges are sessile, filter-feeding
organisms that live in both marine and freshwater environments.
are covered with small intake pores called ostium. A
one-way current carries the water into an internal cavity(spongocoel)
a larger opening, the osculum. The walls of a sponge
are made of two cell layers separated by and embedded in
a gel-like substance called mesoglea. Pinacocytes are leather-like
cells that line the outside wall. Collar cells (Choanocytes)
equipped with flagellum line the inside
cavity and create the one-way water current. Collar cells
trap small particles and plankton. Within the gel-like layer
amoebocytes (amoeba-like cells) distribute food, remove waste,
and build skeletal structures called spongin and spicules.
Spicules are made of silica or calcite. Sponges secrete a
calcite or aragonite base that serves to anchor the organism
to a substrate. Sponges produce both sexually with sperm
and eggs as well
as asexually through budding. The larvae and the collar
cells of sponges are evidence for evolutionary ties to the
flagellated protists. When a sponge dies it disintegrates
leaving the spicules behind. The mineralized spicules
are the part of a sponge that is most likely to be fossilized.
Glass & Calcite
sponges have been divided into three classes. Sponges are
known from Precambrian deposits and representatives
from all three classes range from the Cambrian to the
present. Glass sponges (class Hexactinellida) are represented
by sponges with silica spicules. Members of this class
helped to build massive reefs in the late Devonian. Calcareous
sponges (class Calcarea) are represented by sponges with
spicules. Calcarea sponges were important reef builders
the Permian and Triassic. Common sponges have skeletons
made of the protein spongin (class Demospongea).
fossils that have close affinities with sponges are stromatoporoids,
which were important reef builders during the Silurian
Devonian periods and archaeocyathans, which were the first
multi-cellular reef builders during the Cambrian.
sponges can be used as indicators of paleoenvironments.
Sponges are sensitive to currents, turbidity and depth.
Thus, species of sponges can be clues to the environmental
conditions present during their lives.
Science Olympiad Fossil Event
The 2016 Science Olympiad Fossil List includes the two
genera under the Sponges (Phylum Porifera) category:
Hydnoceras (class Hexactinellida) and Astraeospongia
or Astraeospongium (class Calcarea). Hydnoceras ranges
from Devonian to Pennsylvanian. Astraeospongium ranges
from Silurian to Devonian.