`--gapopen` *string*
: Set penalties for a gap opening. See
  [`vsearch-pairwise_alignment_parameters(7)`](./misc/vsearch-pairwise_alignment_parameters.7.md)
  for a complete description of the gap penalty declaration system. By
  default, the penalty is set to 20 for opening internal gaps and to 2
  for opening terminal gaps, in both query and target sequences.
