Practice question

Balanoglossus is burrowing enteropneust hemichordate inhabiting intertidal mudflats forming U-shaped mucus-lined tubes. Anterior trunk pharynx bears paired dorsolateral gill pores, up to 100 pairs, each comprising gill slit opening to exterior via branchial sac, similar to chordate pharyngeal slits. Ciliary current drives water from mouth through pharynx, exiting via slits, trapping food particles in mucus and allowing diffusion of oxygen across vascularized branchial lamellae. No tracheae, lungs or specialized skin respiration occur. Slit number increases during growth, illustrating respiratory and feeding dual function and deuterostome heritage shared with cephalochordates.