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...