Hi ! Most dynamic way to do it:

my $spec = .... ; # H, M , etc...
my $mod = "mod".$spec ; # Modules named modH , modM , etc..

eval "require $mod;";
if( $@ ){
  die "Cannot load module $mod for specie $spec : $@";
}

#Then, use your module function f1 , f2.. by:

$mod->f1() or $mod::f2() etc...
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This way, anytime you have a new specie to handle you just have to write a new module, without modifying your using code.

In general, avoid to construct case like structure. It makes your code hard to maintain and is a bit outdated.

Dynamicity of perl is easy to write and very rewarding to use. Use it !! J.