different between protonephridia and meyanephridia?
Answers
A metanephridium is a gland involved in excretion, mainly found in invertebrates such as annelids , arthropods and mollusca.
A metanephridium consists of a ciliated funnel opening into the bodycavity connected to a duct which may be variously glandularized, folded or expanded which opens outside the body. These ciliated tubules pump water carrying surplus ions, metabolic waste and moving out of useless hormones through a funnel shaped structure called nephrostones. This waste is passed out of the organism at the site called nephridiophore.
A protonephridium is a network of dead-end tubules, found in the phyla Platyhelminthes, Nemertea, Rotifers and Chordates. The ends are called flame cells(if ciliated) or solenocutes (if flagellated); they perform the function of osmoregulation. The terminal cells are located at the blind end of the protonephridium. Each cell has one or more cilia and their beating inside the protonephridial tube creates an outward going current and hence a partial pressurization in the blind of the tube. Because of this, pressurization drives waste fluids from the inside of the animal. The perforations in the terminal cell are large enough for small molecules to pass, but larger proteins are retained within the animal. Protonephridia are generally found in basal organisms such as in case of flatworms. Protonephridia is likely a defence mechanism which tend to cope with a hypotonic environment by removing excess water from the organism.