You're not enclosing the link tag in quotes. So PHP is probably giving you parser errors when it encounters the first <
because that character doesn't mean anything to PHP in that context. You need to wrap the added HTML in quotes just like the HTML you already have. Something like this:
echo "<td><a href=\"http://mysite.tld/test/blabla/" . $zeile['3'] . "\">" . $zeile['3'] . "<a></td>";
In fact, since variable names are expanded in double-quoted strings, you can simplify:
echo "<td><a href=\"http://mysite.tld/test/blabla/$zeile['3']\">$zeile['3']<a></td>";