Não vi sequer a minhoca.

Vi means I saw. It comes from the verb ver (to see).

This is the 1st person singular of the pretérito perfeito simples in European Portuguese:

• eu vi = I saw
• tu viste = you saw
• ele/ela viu = he/she saw

So Não vi... means I didn’t see...

Portuguese often omits the subject pronoun when it is clear from the verb ending.

So:

• Não vi sequer a minhoca.
• Eu não vi sequer a minhoca.

both mean the same thing: I didn’t even see the worm.

The version without eu is very natural and common.

Não is the standard word for not in Portuguese. It goes before the verb:

• Não vi = I did not see

This is the normal way to make a sentence negative.

Sequer means even in the sense of not even or not so much as.

So:

• Não vi sequer a minhoca.

means something like:

• I didn’t even see the worm.
• I didn’t so much as see the worm.

It adds emphasis, showing that seeing the worm was the minimum thing one might have expected, and even that did not happen.

In Portuguese, sequer is especially common in negative contexts and often sounds a bit more emphatic or formal than some alternatives.

Compare:

• Não vi sequer a minhoca.
• Nem vi a minhoca.
• Não vi nem a minhoca.

These can all suggest I didn’t even see the worm, but sequer has a particular feel of not even / not so much as.

In European Portuguese, sequer is perfectly natural, especially in writing or careful speech.

Here a is the definite article, meaning the.

• a minhoca = the worm

It is not a preposition here. It is simply the feminine singular article, because minhoca is a feminine noun.

So:

• o = the (masculine singular)
• a = the (feminine singular)

Examples:

• o livro = the book
• a minhoca = the worm

Yes, minhoca is a feminine noun.

You can tell in this sentence because it takes the article a:

• a minhoca

Many Portuguese nouns ending in -a are feminine, though not all. In this case, minhoca is indeed feminine.

The structure is very natural in Portuguese:

• Não
  • verb
    • sequer
      • object

So:

• Não vi sequer a minhoca.

This places the emphasis neatly on sequer a minhoca = even the worm.

Other orders may exist in different contexts, but this one is idiomatic and clear.

It is much less natural in ordinary usage. The most natural position here is before the noun phrase:

• Não vi sequer a minhoca.

Putting sequer after the object sounds odd or very marked in this sentence.

For a learner, it is safest to use:

• Não + verb + sequer + noun phrase

Not literally from this exact sentence. Because it uses the definite article a, it specifically means:

• the worm

If you wanted a worm, Portuguese would normally use:

• Não vi sequer uma minhoca.

That means:

• I didn’t even see a worm / not even one worm

So the article matters.

More or less, yes, but with Portuguese pronunciation.

In European Portuguese, vi is pronounced approximately like vee, though the exact vowel quality may be slightly different from English. The important point for a learner is that it is one syllable:

• vi

And não vi is said smoothly together.

Yes. Some alternatives are:

• Nem vi a minhoca.
• Não vi nem a minhoca.
• Nem sequer vi a minhoca.

These all express a similar idea: I didn’t even see the worm.

A few nuance notes:

• Não vi sequer a minhoca sounds neat and natural.
• Nem sequer vi a minhoca is also very common and emphatic.
• Nem vi a minhoca is a bit simpler and more conversational.

It is in the pretérito perfeito simples, which is often the basic past tense for a completed action.

• vi = I saw

So the sentence refers to a completed event in the past:

• Não vi sequer a minhoca. = I didn’t even see the worm.

It is not talking about a habitual action or an ongoing action, but about a specific past situation.