Pinnotherids

Pinnotherids are a group of small decapod crustaceans belonging to the family Pinnotheridae, commonly known as pea crabs. They are notable for symbiotic lifestyles, often inhabiting the gill chambers or mantle cavities of mollusks such as mussels, oysters, and clams, though some species have been recorded in association with other invertebrates. Individuals are typically small, with a smooth, convex carapace and slender legs adapted to maneuver within confined spaces. The family includes multiple genera, such as Pinnotheres and Nepinnotheres, with species described in marine and estuarine waters worldwide.

Pinnotherids are found in coastal ecosystems across warm and temperate seas. Their presence can influence host biology by competing for food or altering host physiology, and in some cases they are considered parasites, while others are described as commensals.

Like other decapods, pinnotherids have free-swimming larval stages, including nauplius and zoea stages, before settling as adults within a host or in the surrounding environment. Their life cycles often involve transmission between hosts and a degree of host specificity that varies among species.

Studying pinnotherids contributes to understanding host–symbiont interactions, crustacean diversity, and the ecology of bivalve-associated communities. Because many species are small and cryptic, taxonomic work and careful host association observations remain important for documenting their ecological roles and evolutionary relationships.