Final answer:
Cephalopods in the Phylum Mollusca are dioecious and lay eggs that directly develop into juveniles, bypassing a larval stage. Female cephalopods often exhibit extensive parental care, and while some cephalopods have reduced or internal shells, nautiluses retain a buoyant, multi-chambered shell.
Step-by-step explanation:
Cephalopods within the Phylum Mollusca are characterized by interesting and unique reproductive behaviors. These organisms are dioecious, meaning they have separate male and female individuals. During reproduction, mating occurs and the female lays eggs in a protected environment. Notably, cephalopods do not produce a trochophore larva, unlike most aquatic mollusks; instead, their eggs develop directly into juvenile forms, bypassing any larval stage. This direct development is an adaptation that allows cephalopods to give birth to more developed offspring, ready to live independently.
In some species, female cephalopods display extensive parental care by protecting and nurturing the eggs for a prolonged duration, which may ultimately lead to the mother's death. The adaptation of internal or reduced shells, such as in squids and cuttlefish, contrasts with their shelled relatives like the nautilus, which possesses a multi-chambered shell used for buoyancy. Furthermore, cephalopods are known for their advanced nervous systems, image-forming eyes, and a closed circulatory system, all of which support their carnivorous and predatory lifestyle.