Final answer:
The function of the suspension feeding device in invertebrate chordates, which includes the pharyngeal slits and endostyle, is to filter and transport food particles to the gut for digestion, supporting the nutrition of organisms like lancelets and tunicates.
Step-by-step explanation:
The suspension feeding device of many invertebrate chordates, such as lancelets and tunicates, plays a critical role in their nutrition. These organisms use pharyngeal slits and an endostyle to filter food particles from the water. Specifically, a current created by cilia draws water in, passing it through the pharyngeal slits that trap food particles in mucus produced by the endostyle. The trapped particles are then transported to the gut for digestion. This feeding mechanism allows them to sustain themselves on microorganisms like phytoplankton.
The notochord, while not part of the feeding process, provides structural support in many chordates and is indicative of the evolutionary path from invertebrate to vertebrate chordates. However, in the adult stage of sessile tunicates, the notochord is lost, indicating its supportive role is less crucial once a sessile lifestyle has been adopted.