( Echinoderms ( ( ( ( ( do not ) ( have ( an exoskeleton ) ) ) but ) ( do ( have ( a ( calcareous endoskeleton ) ) ) ) ) . ) )
(ROOT (S (NP (NNS Echinoderms)) (VP (VP (VBP do) (RB not) (VP (VB have) (NP (DT an) (NN exoskeleton)))) (CC but) (VP (VBP do) (VP (VB have) (NP (DT a) (JJ calcareous) (NN endoskeleton))))) (. .)))
Echinoderms do not have an exoskeleton but do have a calcareous endoskeleton.
(ROOT (S (NP (NNS Humans)) (VP (VBP possess) (NP (DT a) (PRN (-LRB- -LRB-) (NP (NN n)) (-RRB- -RRB-)) (NN endoskeleton))) (. .)))