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Abstract Social predation is a common strategy used by predators to subdue and consume prey. Animals that use this strategy have many ways of finding each other, organizing behaviors and consuming prey. There is wide variation in the extent to which these behaviors are coordinated and the stability of individual roles. This study characterizes social predation by the nudibranch mollusc,Berghia stephanieae, which is a specialist predator that eats only the sea anemone,Exaiptasia diaphana. A combination of experimental and modeling approaches showed thatB. stephanieaedoes predate uponE. diaphanain groups. The extent of social feeding was not altered by length of food deprivation, suggesting that animals are not shifting strategies based on internal state. It was unclear what cues the individualBerghiaused to find each other; choice assays testing whether they followed slime trails, were attracted to injured anemones, or preferred conspecifics feeding did not reveal any cues. Individuals did not exhibit stable roles, such as leader or follower, rather the population exhibited fission-fusion dynamics with temporary roles during predation. Thus, theBerghiaprovides an example of a specialist predator of dangerous prey that loosely organizes social feeding, which persists across hunger states and uses temporary individual roles; however, the cues that it uses for aggregation are unknown. Significance StatementSocial predation is a strategy to hunt dangerous prey and minimize injury. Many nudibranchs specialize as predators of cnidarians, which are dangerous to them. Although nudibranchs are typically characterized as solitary hunters, we provide evidence that social predation strategies may be used by a species that specializes on one species of sea anemone. The study showed that the individual sea slugs assumed temporary roles for establishing groups and that the group dynamics were unstable. However, the cues that the nudibranchs use to aggregate remain elusive. 

Abstract Gastropod molluscs such asAplysia,Lymnaea, andTritoniahave been important for determining fundamental rules of motor control, learning, and memory because of their large, individually identifiable neurons. Yet only a small number of gastropod neurons have known molecular markers, limiting the ability to establish brain‐wide structure–function relations. Here we combine high‐throughput, single‐cell RNA sequencing with in situ hybridization chain reaction in the nudibranchBerghia stephanieaeto identify and visualize the expression of markers for cell types. Broad neuronal classes were characterized by genes associated with neurotransmitters, like acetylcholine, glutamate, serotonin, and GABA, as well as neuropeptides. These classes were subdivided by other genes including transcriptional regulators and unannotated genes. Marker genes expressed by neurons and glia formed discrete, previously unrecognized regions within and between ganglia. This study provides the foundation for understanding the fundamental cellular organization of gastropod nervous systems. 

This review was inspired by a January 2024 conference held at Friday Harbor Laboratories, WA, honoring the pioneering work of A.O. Dennis Willows, who initiated research on the sea slug Tritonia diomedea (now T. exsulans). A chance discovery while he was a student at a summer course there has, over the years, led to many insights into the roles of identified neurons in neural circuits and their influence on behavior. Among Dennis’s trainees was Peter Getting, whose later groundbreaking work on central pattern generators profoundly influenced the field and included one of the earliest uses of realistic modeling for understanding neural circuits. Research on Tritonia has led to key conceptual advances in polymorphic or multifunctional neural networks, intrinsic neuromodulation, and the evolution of neural circuits. It also has enhanced our understanding of geomagnetic sensing, learning and memory mechanisms, prepulse inhibition, and even drug-induced hallucinations. Although the community of researchers studying Tritonia has never been large, its contributions to neuroscience have been substantial, underscoring the importance of examining a diverse array of animal species rather than focusing on a small number of standard model organisms.