EDIT

    '#autocomplete_path' => 'cdm_dataportal/taxonSearch/autocomplete'

    $form['search'] = array(

function cdm_dataportal_taxaon_search_autocomplete($string) {

  $matches = array();

  $queryParams = array();

  $queryParams['query'] = $string."*";

  $queryParams['pageNumber'] = '0';

  $queryParams['pageSize'] = '100';

  $queryParams['doTaxa'] = true;

  $queryParams['doSynonyms'] = true;

  $queryParams['doMisappliedNames'] = true;

  $queryParams['doTaxaByCommonNames'] = true;

  $search_results = cdm_ws_get(CDM_WS_TAXON_SEARCH, NULL, queryString($queryParams));

  foreach($search_results->records as $record){

      $titleCache = $record->entity->titleCache;

      preg_match('/(.*) sec.*/', $titleCache, $trimmedTitle);//remove sec reference

      $trimmedTitle = trim($trimmedTitle[1]);

      $matches[$trimmedTitle] = $trimmedTitle;

  }

  drupal_json_output($matches);

}

  /**