Video Transcript
An unknown species of worm has been
discovered. The body is cylindrical and
bilaterally symmetrical. The organism found is determined to
be a male. What phylum, Platyhelminthes,
Nematoda, or Annelida, is this worm most likely to belong to?
We’ve been told in the question
that the body shape of the worm is cylindrical and also that the body shape is
bilaterally symmetrical. But what did these key terms that
we’ve highlighted actually mean? This is an image of a cylinder. As the worm-in-question’s body
shape is cylindrical, it is shaped vaguely like a long tube. The term bilaterally symmetrical
means that the organism has one line of symmetry along its middle. Humans are also bilaterally
symmetrical as we have one line of symmetry along our center.
If you were to cut a bilaterally
symmetrical organism into two-halves, each side of the dashed line of symmetry would
resemble a mirror image of the other. We know that as this organism is a
worm, it is an invertebrate. Invertebrates are organisms that do
not have a vertebral column, which is also referred to as a spine or a backbone. We need to look at the different
groups of invertebrates that we’re identifying between. So let’s do this next.
A Platyhelminthes, sometimes called
a flatworm, usually has a flattened body. Platyhelminthes tend to be
hermaphroditic, which means that they have both female and male reproductive
organs. Their flattened body might look
something like this.
Nematoda is another phylum of worm,
and they are sometimes called nematodes. They usually have
cylindrical-shaped bodies. Nematodes can either be male, or
they can be female. Their body might look something
like this.
Let’s take a look at our last
phylum of invertebrates, annelid worms. Annelids are worms that belong to
the phylum Annelida, and these worms have segmented bodies. Segmented means that their body is
divided into distinct rings or sections that might look something like this. Annelid worms can be male, female,
or hermaphroditic.
Let’s use the information in the
question to work out what phylum of invertebrates this newly discovered worm is
likely to belong to. Our organism in question is
male. This could mean that it is an
annelid or a nematode but probably not a platyhelminth, as most organisms in this
phylum are hermaphroditic. As the body shape of this organism
is cylindrical, this most closely matches the body shape of organisms within the
phylum Nematoda and not the segmented annelid worms. Therefore, this unknown species of
worm is most likely to belong to the phylum Nematoda.
