A. Sponges--Colonies rather than individuals. No movement except
for individuals cells and the movement of water through the
animal due to the movement of the flagellae of the choanocytes.
1. Levels of construction
a. Asconoid--Simple vase shaped sponges with body wall
essentially two layers thick, an outer layer of
pinacocytes and an inner layer of choanocytes. There
are pores through the body wall to connect the
outside with the spongocoel. Spongocoel empties via
the osculum to the outside. Middle layer composed
of spicules and miscellaneous cells.
b. Syconoid--Vase shaped, but larger. Body wall has
indentations, the incurrent canals, which empty via
pores into the choanocyte chambers when then empty
into the spongocoel. Spicules are also found in the
body wall
c. Leuconoid--The most complex pattern. Choanocytes are
in choanocyte chambers which are connect to the out
side via incurrent canals and to the spongocoel via
excurrent canal. There many be many spongocoels and
therefore many oscula. The canals and chambers are
enmeshed in a mesh-work of spongin spiclues.
2. Design factors
a. As the flagellae on the choanocytes beat, they force
water out of the sponge. This produces a slight
negative pressure which then allows for the movement
of water into the sponge from the outside. The
collar on the choanocyte is actually produced from
the fusion of microvilli that extend from the cell
membrane and encircle the flagellum. Food particles
caught in the current get stuck to the collar and
get entrapped in a food vacuole which then circulates
through the cytoplasm.
b. Volume of fluid moving through creature can be quite
large, large enough in some of the loggerhead sponges
of the Carribean to produce a roiling of the water
above the sponge. Osculum has to be high enough
off the rest of the sponge so that the excurrent flow
moves beyond the colony, so that there is no
recirculation of the materials back in through the
incurrent pores/canals.
c. One would expect that fresh water sponges living in
quite environments would have high oscula, those
living in environments with flowing water, lower
oscula, as the water current flowing over the sponge
would carry materials away.
B. Cnidaria
1. Movement in the polyp-type individuals.
a. Basic pattern of construction is two layers with
middle mesoglea. Inner and outer layers have
muscle fibers in their bases, which produces
circular and longitudinal muscles. These are
antagonistic to each other and contract against
a skeleton formed of the water trapped in the
gastrovascular cavity.
b. Contraction of circular muscles make polyps long and
tall, contraction of longitudinal muscles make polyps
short and squat. Opening into gastrovascular cavity
must remain shut if gastrovascular fluid is to act
as skeleton.
c. Hydra can therefore move by doing sommersaults, that
is, bending over and attaching to substrate by
tentacles, flipping and then re-attaching by base.
The can also move by pedal creep, where the base
slowly moves along the substrate. Lastly the pedal
disk may secrete a bubble of gas and float up to the
surface. It then drops off the bubble and reattaches
to the substrate.
2. The Anthozoan polyps
a. Anthozoan polyps are structurally more complex than
the hydrozoan polyps. The body consists of a number
of primary, secondary and tertiary septa that pass
from the outer body wall to the inner stomodaeum or
gullet, and extension from the oral disk that passes
towards the pedal disk. These septa or mesenteries
are paired. Inaddition to the cicular and longi-
tudinal muscles of the body wall, there are longi-
tudinal muscles attached the inner sides of the
paired septa.
b. The polyp uses the same game plan of contracting
against the fluid in the gastrovascular cavity.
In addition, they can force the fluid out and
contract into a small blob. There is some
restoration of shape because of decompression. Also
the gullet has a ciliated band that runs the length
of the gullet and can cause a movement of water
into the gastrovascular cavity.
c. Anthozoan polys are pretty stationary, but can
also move by pedal creep. This can be readily
seen in "fights" between different clones of the
same species where the lines advance/attack and
retreat.
d. The polyps of corals sit in a cup or thecae composed
of calcium carbonate. The cup may have slender
fin-shaped structures that actually are between
the mesenteries.