are carnivores. Favorite prey items include bivalve molluscs
such as oysters, clams, and mussels. But polycalds cannot
just swallow entire mussels or clams. Instead, they slip between
the valves of the oyster and once inside, push out their pharynx
(feeding tube). Because of this, they are considered pests
by oyster farmers worldwide. The way in which they enter their
prey is still not known. Some scientists think that the worms
just slip in when the valves are slightly gaping, whereas
others speculate that the worms produce some toxins that act
as either anaesthetics or irritants.
specimens of Imogine mcgrathi snacking on an
reefs, polyclads like to feed on sedentary colonial animals
such as ascidians. Worms can glide over the surface of the
colony and suck out individuals one at a time, or many all
at once. For example, the pharynx of Pseudoceros is branched
into sections and so the worm can feed on many ascidian individuals
bifurcus extending its branched pharynx and feeding
the everted pharynx of a Pseudobiceros sp.
within the housing of an ascidian. Photo courtesy of
enters the pharynx it moves into a highly branched cavity.
In fact, polyclads get their name from this branched digestive
system ("poly" = many; "clade" = branches).
These branches reach throughout the body to deliver digested
food to the remainder of the animal. Most flatworms do not
have an anus, so what goes in the mouth and cannot be digested
and pass on to the gut cells, is expelled again via the mouth.
sp. showing multibranched intestine through the body wall.
Photo by RF Bolland©, used
is partially extracellular and partially intracellular. Nutrients
can diffuse into the body and may be moved around by cells
in the parenchyma. Polyclads, like all flatworms, have no
circulatory or respiratory systems. So, transport within their
bodies is via diffusion. Food reserves are stored as fats
and starving polyclads will use up these reserves. If starvation
continues, the worms gradually regress in size because they
are mobilizing their own tissues for food. Polyclads can survive
up to 6 months without feeding.
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pages are for educational purposes only. If you use any of
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these web pages. © MK Litvaitis, 2005
credits to Leslie Newman, Andrew Flowers, or Anne DuPont,
unnless otherwise indicated.