Final answer:
Osphradia are the ciliated sensory pits or slits associated with mollusks responsible for chemoreception in food gathering, making d. Osphradia the correct answer. They are important for detecting chemical changes in the environment, particularly food presence.
Step-by-step explanation:
The question asks which organs are ciliated sensory pits or slits that appear to be chemoreceptive for food gathering. The correct option is d. Osphradia. Osphradia are sensory structures associated with mollusks that are responsible for chemoreception, which allows these organisms to detect chemical changes in their aquatic environment, particularly in relation to the presence of food and potentially harmful substances. They are typically located in proximity to the gills where they sample the incoming water, assessing the quality and presence of food particles.
Nuchal organs, on the other hand, are sensory structures found in annelids such as polychaete worms and are also thought to have chemoreceptive functionality. Statocysts are sensory organs found in various invertebrates that serve to provide the organism with a sense of balance and spatial orientation. Nephridia are the excretory organs of certain invertebrates, including annelids, that filter waste from the blood and excrete it from the body.
In contrast, osphradia are specialized for chemosensory activity, vital to the survival strategies of mollusks for detecting food sources and avoiding predation by sensing harmful stimuli in the water. They play a critical role in feeding mechanisms and the orientation response of these aquatic organisms.