So what is the main difference between platyhelminthes and this Nematodes? It says it in the name. Platyhelminthes are acoelomate (no coelem), and Nematodes are pseudocoelomates meaning they have a false body cavity.
This false body cavity allows oxygen through the body, and there is also a complete gut meaning a combination of this and the false body cavity allows nutrition to travel through the body. It also makes the worm rigid acting as a hydrostatic skeleton.
Phylum Nematoda
The main focus psedocoelomates will be Nematodes, for no other reason other than I need to remember this group and so do you now.
The name comes from nematos which means “thread” and they are roundworms, which is another difference between Nematodes and Platyhelminthes (which are known as flatworms).
So are there any similarities between these two groups? Yes! Both platyhelminthes and Nematodes have bilateral symmetry and they are triploblastic with three germ layers. Now as cool as that is we need to now solely focus on nematodes.
Eating?
They have a complete gut so the food can travel from mouth to anus. This effectively gathers nutrients and allows continuous eating (which is fantastic because eating is great!!).
There is a triradiate pharynx which allows for suction of the food, and this is characteristic for nematodes.
There are some iffies however, such as the intestine is non muscular so how does the food move? The food moves by the worm moving its body and new food entering the body.
Moving places?
There are only longitudinal muscles but this allows them to move in sinusoidal undulations, or in english they move like waves.
Muscle-nerves… what?
So any group I talk about from here on will be cephalized, but this group has an interesting thing where the muscles actually grow out to reach the nerves for communication. In humans nerves and muscles are interconnected which is pretty different.
Sexy time?
They are sexual and dioecious, and there is internal fertilization which seems more familiar to most humans who have done the deed or know of the deed.
The males have a copulatory spicule which holds the female vulva open and the future babies will enter.
The babies will lose the flagella and become amoebic (travels with pseudopodia), as the female has high hydrostatic pressure!
So there are a number of different worms in this group, and we will start by looking at Roundworms.
Roundworms (Ascaris lumbricoides)
This is a human intestinal parasite which can reach more than 40cm long which is prety disgusting. A way to be infected can be by children putting dirty fingers in mouth or eating uncooked vegetables (as a former vegetarian I can tell you vegetables are already un-enjoyable as it is and knowing this makes it way harder to want to be a vegetarian again).
Hookworm (Necator americanus)
They are blood sucking internal parasites with hooks on the mouth for attachment. I like to remember these guys as vampires because they want your blood (and lungs).
Pinworms (Enterobius vermicularis)
These guys love the human cecum and large intestine, but one thing to remember is that it is highly infectious so if someone in a house hold has it everyone has to be treated.
Guinea Worm (Dracunculus medinensis)
This is a vicious worm who lives right under the skin with a copepod as the intermediate host. This is common in poorer countries where dirty water is an issue as that is how it is usually transported. The only way to remove it is to superficially pull it out which is known to be extremely painful.
Filarial Worm (Wucheria spp.)
This lives in the lymphatic system with a vector being the mosquito. This is known to cause swelling of the lymphs, leading to fluid accumulation and thickened skin causing Elephantiasis.
Heartworm
The mosquito is a vector also in this group, and it infects cats, dogs, sea lions and sometimes even humans! I did not place any pictures as they are fairly graphic so just google it in your own leisure!
So this is the nematodes! However there is a group on the next blog which will be fairly complex and from now on all the phylums I discuss will be… coelomate!
superbfairyjacyntha 