Sabrina Karim, A-Band. Lab Essay: Marine Worms

Flatworms belong to the phylum Platyhelminthes. They have the simplest kind of

body structure. Out of all the bilaterally symmetrical animals, they have the simplest

body plan. They get their name because their bodies are compressed. Their mouth is the

only opening into their digestive cavity. Both food is taken in through their mouth, and

waste is discharged. Flatworms have a well defined nervous, muscular, excretory, and

reproductive system. They distribute the food they digest through a digestive tube that

spreads out all throughout the body. Since these worms are bilaterally symmetric, it

enables them to be able to move from place to place more efficiently, which means they

can get food easier, and get away from predators just as easy as well. If they were not

made up as so, they would not have much control over their body movements, which

would make it nearly impossible for them to survive in the ocean. This also means, that

their bodies have a distinctive head and behind, and that both their right and left sides

are mirror images of each other. A unique factor of the worms of the phylum

Platyhelminthes is that they are light sensitive, so they avoid brightly lit areas often.

They have many regenerative properties, which helps because they like to crawl into

and under the rubble, and sometimes the rubble will tear the skin of the flatworm.

Flatworms are usually spotted at the bottom of the ocean, but only rarely do you spot

some swimming. They are mostly spotted in shallow rubble zones.

Ribbon worms belong to the phylum Nemertea. The body structure of this worm

is that, the foregut, stomach, and intestine run a little below the middle of the body, and

the anus is at the tip of it’s tail, and the mouth is under the front. A little above where the

gut is, is a cavity that runs mostly above the midline and ends a little short above the rear

of the body. This cavity is called the rhynchocoel. The rhynchocoel is what really helps

the ribbon worm to catch it’s prey. Usually, it remains inactive, but then it turns inside

out to come above the mouth and capture the prey with venom. At least one pair of

ventral nerve cords connect to the brain and run along the length of it’s body. This worm,

as other Nemerteans, respire through their skin. It doesn’t have a heart, so the flow of

fluid depends on the contraction of muscles in the vessels and body wall. All nemerteans

move slowly, they use their external cilia to glide on surfaces and leave a trail of slime.

Only a few ribbon worms live in the open ocean, they mostly making living or hiding

places on the bottom of the ocean.

Roundworms belong to the phylum Nematoda. They have no skeleton.

Roundworms have a definite digestive system, which runs as long as the length of their

body. They have a mouth, pharynx, intestine and anus. Most roundworms are known as

parasites. They live off of other animals and plants. A roundworm has two nerve cords

that transmits impulses to the body, they don’t have a heart or any formal blood vessels.

They don’t have a formal respiratory system either. Roundworms are bilaterally

symmetric as well. Roundworms reproduce sexually and over 200,000 eggs can be

deposited at once after they are fertilized. In order to excrete, the roundworm has an

anus at the rear end and many excretory tubes that end in an excretory pore. Roundworms

are mostly found in the Intertidal zone.

Sandworms belong to the phylum Annelida. The body of the sandworm is similar

to that of an earthworm. Its body is either ringed or segmented. It’s head end, is a black-

red sort of color and it passes into the middle part of