List of directories within a directory

I have a directory with 200 sub directories in it. How do I create a
list of the sub directory names?

I know how create a list of all the files in a directory:

opendir(DIR, $dirname) or die "can't open $dirname: $!";
while (defined($file = readdir(DIR))) {
next if($file =~ m/^\./);
next if($file eq "");
push (@filenames, $file);
}
closedir(DIR);

but how do I do it for the directories within a directory

Al Moodie.
.