Taenia as a parasite
Taenia is an endoparasite
The pork tapeworm Taenia solium has two hosts. It spends part of its lifecycle inside pigs (hence the name) and part of its lifecycle inside humans.
This diagram (which comes from http://www.path.cam.ac.uk/~schisto/Tapes/Taenia.html) shows the lifecycle of the pork tapeworm.
From the diagram you can see that the adult form is found only in humans.
The adult releases eggs which infect pigs (and also other humans).
The egg develops within pig muscle to form a larva.
The larva is infectious so consumption of poorly cooked pork can result in infection of humans. Correct cooking will kill the larva rendering pork safe.
The adult form has a definite head end called the scolex
The remainder of the body is made up of segments called proglottides
These photos (taken from http://home.clara.net/fidai/coolstuff/wormmansamazingparasitepage.htm) show the scolex and a proglottis)
This drawing (which comes from http://darwin.nmsu.edu/cgi-bin/moreinfo.cgi?10765) shows a proglottis.
As you can see it contains male reproductive structures as well as numerous ovaries.
The proglottis is thus able to self-fertilize.
The proglottides furthest from the scolex are fully mature and, following self-fertilisation, these proglottides, bearing numerous fertilized eggs, detach from the rest of the organism and are shed in faeces.
If the shed proglottides are consumed by a pig (or by another human) the eggs will develop to form larvae which can burrow into the muscle of the host.
Note that neither the proglottides or the scolex contain any digestive structures
Both of the above images of the scolex of Taenia come from www2.austin.cc.tx.us/microbugz/ 53helminth.html
They show the hooks and suckers that the scolex uses to attach itself to the wall of the host's small intestine
Nurtition
As stated, there are no digestive structures in Taenia - the tapeworm gets its nutrients by the absorption of the digested food of the host across its body surface.
The adaptations present to facilitate this mode of nutrition are:
- a protective outer coating (tegument) made of protein and chitin - this protects against the host's digestive enzymes
- the proglottides are flattened - resulting in a large surface area to volume ratio for absorption
Other adaptations to a parasitic lifestyle:
- production of numerous offspring
- reduction in superfluous complex structures and
organs such as sense organs or a nervous system
- the previous two adaptations are typical of parasites
- Taenia is adapted for life in the human gut because it has a low oxygen requirement
- it also possesses the hooks and suckers already mentioned
This photo (although of poor quality) gives some indication of the size of the pork tapeworm Taenia solium. It comes from http://martin.parasitology.mcgill.ca/JIMSPAGE/TAENIA.HTM
Some links:
http://darwin.nmsu.edu/cgi-bin/moreinfo.cgi?10765
Pictures of Taenia
http://www.path.cam.ac.uk/~schisto/Tapes/Taenia.html
More information than you could ever need about Taenia
http://www.curriculumpress.co.uk/pdf/newbio/53%20Parasites.pdf
Curriculum Press' pdf document on the subject of parasites - only one page was showing when I tried it but just in case the rest reappear here's the link
http://home.clara.net/fidai/coolstuff/wormmansamazingparasitepage.htm
A mildly amusing look at some of the nastier parasites including Taenia - good photos