$string = <DATA>;

$right = quotemeta('</a>');
($temp, $id)= $string =~ m/(Gallus\sgallus|Chicken).*?([0-9]+)>.*?$right.*?\n/i;

print "$temp: $id\n";

__DATA__
<a href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=Nucleotide&list_uids=18656900&dopt=GenBank" >gb|AF468789.1|</a>  Gallus gallus LIM domain-containing transcri...   <a href = #18656900> 48</a>   0.006

##</code><code>##

Gallus gallus: 18656900