Here's a short story:

The Bilateria or bilaterians, or triploblasts, are animals with bilateral symmetry, i.e., they have a head ("anterior") and a tail ("posterior") as well as a back ("dorsal") and a belly ("ventral"); therefore they also have a left side and a right side. In contrast, radially symmetrical animals like jellyfish have a topside and a downside, but no identifiable front or back. 

The bilateria are a major group of animals, including the majority of phyla but not sponges, cnidarians, placozoans and ctenophores. For the most part, bilateral embryos are triploblastic, having three germ layers: endoderm, mesoderm, and ectoderm. Nearly all are bilaterally symmetrical, or approximately so; the most notable exception is the echinoderms, which achieve near-radial symmetry as adults, but are bilaterally symmetrical as larvae. 

Except for a few phyla (i.e. flatworms and gnathostomulids), bilaterians have complete digestive tracts with a separate mouth and anus. Some bilaterians lack body cavities (acoelomates, i.e. Platyhelminthes, Gastrotricha and Gnathostomulida), while others display primary body cavities (deriving from the blastocoel, as pseudocoel) or secondary cavities (that appear "de novo", for example the coelom). 

The hypothetical most recent common ancestor of all bilateria is termed the "Urbilaterian". The nature of the first bilaterian is a matter of debate. One side suggests that acoelomates gave rise to the other groups (planuloid-aceloid hypothesis by Graff, Metchnikoff, Hyman, or ), while the other poses that the first bilaterian was a coelomate organism and the main acoelomate phyla (flatworms and gastrotrichs) have lost body cavities secondarily (the Archicoelomata hypothesis and its variations such as the Gastrea by Haeckel or Sedgwick, the Bilaterosgastrea by Gösta Jägersten , or the Trochaea by Nielsen). (End of story)

Provide your best guess for the following question. Give ONLY the guess, no other words or explanation.

For example:

Guess: <most likely guess, as short as possible; not a complete sentence, just the guess!>

Here are a few examples of questions and answers:

Question: what is this article about?
Guess: The bilateria

Question: are they considered animals?
Guess: Yes

Question: are sponges part of them?
Guess: No

Question: what else are they called?
Guess: bilaterians,

Question: or?
Guess: triploblasts

Question: what is the scientific name for the tail?
Guess: posterior

Question: what about belly?
Guess: ventral

Question: do they have a head?
Guess: Yes

Question: what is the other word for head?
Guess: anterior

Question: do all of them have a separate mouth and anus?
Guess: yes

Question: what has germ layers?
Guess: bilateral embryos

Question: how many layers?
Guess: Three

Question: please name them
Guess: endoderm, mesoderm, and ectoderm

Question: what is the most recent ancestor called?
Guess: the "Urbilaterian".

Question: is there anything that doesn't have a front or back?
Guess: Yes

Question: what?
Guess: jellyfish

Question: what do they have?
Guess: a topside and a downside

Now answer the following question in the same format.

Question: give me examples of phyla please.

flatworms and gnathostomulids