Among the groups , which one have no systematic program for their elimination ?
They share , among other things , an exoskeleton consisting of α - chitin and non-collagenous proteins ; gonads and waste - elimination organs enclosed in true coelom tissue ; an open blood system with a tubular heart situated at the rear ; an abdominal cavity divided into pericardial and perivisceral cavities ; respiration via tracheae ; and similar embryonic development .