Question

Are organisms in class Cestoda (or tapeworms) cephalized? Shown a photo of a tapeworm I was asked if the organism shown was of class cestoda, class trematoda or cephalized or both a cestode and cephalized or a cestode and a trematode. Tapeworms have bilateral symmetry so I assumed that they are cephalized and marked cestoda and cephalized but my answer was marked as incorrect.

Answer 1

I'm pretty sure cephalisation is a standard flatworm characteristic - they certainly do have some sort of concentration of nervous tissue at the front end. But are you sure that the photo was of a tapeworm and not a fluke (Trematoda)? Was it long and segmented and have a small "head" (scolex) at one end? Or was it unsegmented, possibly with a more oval body shape? Did it have eyes?

Answer 2

no as calliope said cephalisation started from platyhelminthes but still incomplete complete cephalisation occur from annelieds :)

Answer 3

Hm, my textbook agrees with you, heena (to an extent: it claims that complete cephalisation is an arthropod apomorphy, though annelids are certainly most of the way there). But I have also seen cephalisation defined as a mere concentration of nervous tissue at the front end, and flatworms definitely have that.

Incidentally, my question above as to whether it had eyes was to rule out free living flatworms, just in case the animal in the photo was neither a trematode nor a cestode.

Answer 4

if we only talk abu cephalisation i mention abu complete and incomplete and faltworm is in phylum platyhelminthes means cephalisation occur firt time but not completely it takes time and complete develop cephalisation occurs in annelied that is earthworm

Answer 5

first thing i wanna tell u cephalisation dont means it contains eyes ok
like earthworm had complete cephalisation but still lack eyes ok

Answer 6

I'm still not convinced that annelids have complete cephalisation. They definitely have something resembling a brain in the first couple of segments, and the mouth is also in that region, but like in the case of flatworms, the head region is not clearly defined. It's hard to just look at an earthworm and say where the "head" stops and the body begins. Arthropods (e.g. insects) generally have clearly-defined heads (note that "cephalisation" comes from the Greek word "cephale", meaning "head"), and I think that's why my textbook lists cephalisation as an apomorphy for that phylum.

Answer 7

Oh, and heena is right that cephalisation does not mean that eyes are present. However, if you see an animal with eyes at one end, that is evidence of cephalisation, or at least the beginning of the process, because it indicates a concentration of nerve tissue at that end of the body.

Answer 8

ok ok come to chat i ll xplain u ok