The
Wrinkled Star Pteraster militaris
We have found
only one species which is likely to be a predator. This is Wrinkled
Star, Pteraster militaris. It is occasionally observed
with the stomach everted over a living Cloud Sponge which
is highly suggestive of feeding. It is also
reported to feed on another species of sponge and on certain
hydrocorals. |
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Henricia
sanguinolenta
The white thin armed sea star Henricia sanguinolenta. Is occasionally seen on
living Cloud Sponges but it is unclear whether or not it is feeding on sponge
tissue.
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Desmacella
austini in a Cloud Sponge
Several kinds of sponges take up residence within the skeletal framework of dead
Cloud Sponges. At least one of these, Desmacella cf. vestibularis, extends
in dead skeleton to the edge of living tissue.
It is possible that it kills the sponge, not for food but for
habitat.
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However,
with the exception of two or three predators noted above, only mobile species of crustaceans and
fish have been found
on living sponges. Many sponges produce chemicals which may
be toxic, distasteful or act as a repellant. Ray Anderson,
a biochemist at Univ. of British Columbia has been unable
to find any such compounds in Cloud Sponges. Could there
be some physical deterrent?
We employed members of three species to examine the surfaces
associated with locomotion after contact with the outer sponge
surface. Each specimen was placed in contact with the sponge for
four to five minutes. |
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| Limpet
ventral view with projecting spines
On a limpet
we found on the order of 100 spines projecting from the
foot, the mantle edge and around the mouth |
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| Urchin
on sponge
Sea urchins
use a combination of spines and tube feet to move over the
sponge. |
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| Tube
foot under low magnification
Many of the
tube feet were pierced by 1-3spines to depth of up to 1mm |
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Tube
foot under high magnification
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| Side
view of sponge surface
The spines
are limited to the outer surface and are oriented vertically
with the thorns pointed toward the sponge. The knob like
structures are the spiny ends of 6 rayed pinnules. They
appear to guard the pores entering the sponge. However,
their role in this regard has not been established. |
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I sacrificed a finger
to show that the same holds true for spongologists!!
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| Scanning
electron micrograph of spine
The orientation
of the spinelets are reminiscent of those in a porcupine
and presumably serve the same purpose.
However, these spines do not provide absolute protection against soft bodied
animals. We found a brittle star inside a sponge which earlier had been outside.
It must have crawled up the outer surface to get in, where it resided for several
weeks. Also, there are soft bodied predators on these sponges. Discussed.
in the predator section. |
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| Spider
crab
Spines were
not seen on the feet of a spider crab and presumably
cannot penetrate the hard outer skeleton. The same would
be true for shrimp and squat lobsters. No spines were
found on any of these animals when they were
placed on the inner surface of a sponge. |
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When all or a portion of a sponge dies all the loose
spicules, including the spines, are washed out and only the
fused main frame remains.
These skeletons become available as substrate for a variety
of organisms.
More information on this subject can be found under HABITAT |
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