In: Biology
A)How are the cnidocytes distributed over the body of Hydra? Does their distribution suggest anything about their function? what?
B)In what way does the mesoglea of the cnidarians differ from the mesohyl of the poriferans?
c) what happens to a Hydra when the epithelia-muscular cells that run parallel to the long axis of the body contract? what happens then those cells that run perpendicular to the long axis of the body contract?
A, In Hydra, almost continuous neoproduction of cnidocytes occurs within the intercellular spaces of the ectodermal body epithelium, while the majority of functional cnidocytes are located within the large ectodermal epithelial cells (battery cells) covering the highly mobile filiform tentacles. Thus, the replacement of used tentacular cnidocytes involves an extensive migration of these cells from the body into the tentacles. However, some functional stenoteles and isorhizas remain positioned in the body ectoderm. Although their respective functions are not fully understood they may defend this body region against predators and/or epibionts
B. Mesoglea is the translucent, non-living, jelly-like substance found between the two epithelial cell layers (i.e., between the ectoderm and endoderm) in the bodies of cnidarians. It is referred to the tissue found in jellyfish which functions as a hydro-static skeleton. The mesoglea is mostly acellular but in cnidaria, it contains muscle bundles and nerve fibres. Mesohyl generally refers to tissue found in sponges.
C. The longitudinal ectodermal muscles are involved in contraction responses of hydra while endodermal circular muscles are involved in polyp extension. In Hydra, a pacemaker system regulates this process. It is constituted by a small subset of nerve cells connected by gap junctions located near the foot, and are capable of synchronous firing.