( They ( ( ( ( have ( ( retained ( much cartilage ) ) ( in ( the ( skeletal system ) ) ) ) ) and ) ( have ( ( bony plates ) ( covering ( the ( semicartilaginous skull ) ) ) ) ) ) . ) )
(ROOT (S (NP (PRP They)) (VP (VP (VBP have) (VP (VBN retained) (NP (JJ much) (NN cartilage)) (PP (IN in) (NP (DT the) (JJ skeletal) (NN system))))) (CC and) (VP (VBP have) (NP (NP (JJ bony) (NNS plates)) (VP (VBG covering) (NP (DT the) (JJ semicartilaginous) (NN skull)))))) (. .)))
They have retained much cartilage in the skeletal system and have bony plates covering the semicartilaginous skull.
(ROOT (S (NP (NNS Hagfishes)) (VP (VBP have) (NP (NP (DT a) (NN skull)) (VP (VBN made) (PP (IN of) (NP (NN cartilage)))))) (. .)))