Translation:The very first animals lived in the seas.
Correct English is the following:
1. ... lived in seas.
2. ... lived in the sea. [sing.]
"the seas" here sounds like something a non-native speaker might say.
Asi proto, že jsou jen dvě možnosti, v mořích/na pevnině. Neznamená to "v různých mořích". Ale vařím z vody,.
Já už jsem z těch "členů" nešťastný. I am desperate of the articles. I don't understand why i must use the article "the" before "seas". Can you explain it someone?
You do not need the article "the" here, in my opinion. See my comment below.
We say "incorrect".
It is not incorrect, I have just added it. Ngrams however still shows more hits for "lived in the seas" in comparison to "lived in seas".
The number of hits has nothing to do with if a sentence is correct or not. In that sentence, I have no idea what are the seas you are referring to, hence I would put seas in general without an article.
The numbers show tendencies and preferences and their examination shall always be followed by examination of the actual sentences. There you will see that book authors do really use "in the seas". You do not have to know which particular sea with some name was it. It is either the seas (all of them in general) or the land.
I suggest to not underestimate the value of corpus searches. They can help you to find surprising stuff even about your own native language. I have learned a lot about Czech, for instance.
Apparently, I cannot reply directly to you.
I agree that "The very first animals lived in the seas." is correct. However, I have no ideas whether it is some specific seas that you mentioned before, the seas in general (all the seas) or a portion of all the seas (2 seas out of 4 seas). If I don't know in which category it is, I can say "in seas" and the statement remains true.
In addition, from the Czech sentence, there is no way to guess which case it is. It is written "v morich" without any stress on "the seas".
Finally, I am using Duolingo to learn Czech, not English. One should keep that in mind. I do make mistakes in English, however this is a different matter. Semantics is unrelated with the number of hits