Prosobranchia
Prosobranchia, a former subclass of gastropod molluscs, is characterized by the presence of one, and rarely two, gills positioned in front of the heart. These molluscs are known for their diverse array of shell shapes and structures, with fossilized examples dating back to the Upper Cambrian period.
Prosobranch snails, a subclass of gastropod molluscs, possess gills located in front of the heart. The gill cavity is oriented forward and resides on the dorsal side of the organism.
The majority of prosobranchs possess a shell, typically spirally coiled, although some may have a cap-like or dish-like shape. Their diet primarily consists of vegetation, facilitated by a radula, although other feeding habits such as detritus, filtration, predation, and parasitism are also observed. Most species possess a well-developed radula, with herbivores featuring robust teeth and detritivores having weakly chitinized teeth. Predatory prosobranchs primarily prey on bivalve molluscs and echinoderms, although some species may consume coelenterates and sponges. Parasitic species have undergone significant physiological modifications, such as the loss of their shell, intestine, heart, and other organs.
Sensory organs found in prosobranchs typically include simple eyes, statocysts, a pair of cephalic tentacles, and osphradia.
The foot of prosobranchs is well-developed, often appearing as a bulky muscular outgrowth in primitive forms. It commonly possesses a horn-like or calcified operculum that seals the shell's opening when the mollusk retreats into it. The foot primarily functions for crawling and substrate support, although some species may employ it for burrowing or transformation into an attachment or swimming organ in specific environments or planktonic species.
While predominantly gonochoric, prosobranchs also exhibit hermaphroditic characteristics.
