Digestive System Evolution

[Daniel Mariner]

I need to know how was the digestive system evolution since the beginning I mean since that beings with just one cell. (sorry for the bad english)

[protozoan]

Theres too types of digestion, intra and extracelular digestion. Intracelular digestion is fylogenetically older than extra. The most intracelullar digestion appears in unicellular organisms, some of them can have specialized structures through which they intake food like cytopharynx, cytostoma, food vacuoles. In multicelular orgs theres 3 types of digestive systems.
1. Digestive cavity - in phyllum Porifera - intracelular digestion which realize through epithelium of choanocytes.
2. Digestive duffle - in orgs with diploblastic body plan - Cnidaria, Acnidaria (Coelenterata) - this has only one opening - mouth(thats why duffle), intracelular digestion changes to extracelular digestion.
3. Digestive tube - Bilaterally symetrical orgs - this has two openings - mouth and anus (thats why tube), theres extracelular digestion.

Theres a lot of exceptions. For example gastropoda has uni and extra together.