You can't go wrong. Do it either way. The only difference is in how you think about the word "seagull". You can think of it as a single thing (a kind of bird) or you can think of it as a category that contains many things, as in "there are many species of seagull". I personally favor "types of seagull" but I do not claim that is the only way to do it. I have never found talk about "countable" and "uncountable" nouns to be helpful. Which one a word is depends on how you choose to think about it. Concentrate instead on what you think each word describes. Often there is not a single correct answer.

Here you are using countable nouns: "type" and "seagull" So you have to either use only the singular forms or the only the plural forms. "Some types of seagulls" "Some type of seagull" I hope that helps

Hello madam, good morning to you. I would like to learn your language while I teach you mine. Looking forward to hear back from you have a nice day.