(a) ventral tubular nerve cord
(b) pharynx with gill slits
(c) pharynx without gill slits
(d) absence of notochord.
Ans: (b) pharynx with gill slits
Sol: An important characteristics that hemichordates and chorddates share is presence of pharyngeal gill slits. Gill slits are dorsal in position in hemichordates whereas they are lateral in chordates. A true unotochord does not occur in hemichordates. Nervous system is distinctly of vertebrate type being intraepidermal in position and having a ventral nerve cord.