sessilida

Sessilida is a taxonomic group within the order Decapoda, specifically referring to crustaceans that are sessile in their adult stage. This means they are permanently attached to a substrate, unlike their motile larval forms or other decapod crustaceans that can move freely. The most well-known examples of sessilida are barnacles, which belong to the infraorder Cirripedia. These animals cement themselves to various surfaces, including rocks, ship hulls, whales, and even other marine invertebrates.

The sessilida lifestyle involves a significant metamorphosis from a free-swimming larval stage to a permanently attached adult form. Once attached, they typically develop a hard calcareous shell or carapace for protection. Feeding is achieved through specialized appendages, often modified into feathery structures called cirri, which are extended into the water column to filter out small planktonic organisms. Reproduction in sessilida can be complex, with many species being hermaphroditic, possessing both male and female reproductive organs. Some sessilida also exhibit parasitic behaviors, with certain species of barnacles infesting other marine animals. Despite their immobility as adults, sessilida play important roles in marine ecosystems as filter feeders and as a food source for other organisms.