No abstract

Chemoreception might play an important role for endemic shrimp that inhabit deep and dark hydrothermal vents to find food sources and to locate active edifices that release specific chemicals. We compared the chemosensory abilities of the hydrothermal shrimp Mirocaris fortunata and the coastal related species, Palaemon elegans. The detection of diverse ecologically relevant chemical stimuli by the antennal appendages was measured with electroantennography. The 2 species can detect food-related odor and sulfide, a short-distance stimulus, via both their antennae and antennules. Neither iron nor manganese, considered as long-distance stimuli, was detected by the antennal appendages. Investigation of the ultrastructure of aesthetasc sensilla revealed no specific features of the hydrothermal species regarding innervation by olfactory sensory neurons. Pore-like structures occurring in the aesthetasc cuticle and dense bacterial covering seem to be unique to hydrothermal species, but their potential link to chemoreception remains elusive.

Alvinocaridid shrimps are emblematic representatives of the deep hydrothermal vent fauna at the Mid-Atlantic Ridge. They are adapted to a mostly aphotic habitat with extreme physicochemical conditions in the vicinity of the hydrothermal fluid emissions. Here, we investigated the brain architecture of the vent shrimp Rimicaris exoculata to understand possible adaptations of its nervous system to the hydrothermal sensory landscape. Its brain is modified from the crustacean brain ground pattern by featuring relatively small visual and olfactory neuropils that contrast with well-developed higher integrative centers, the hemiellipsoid bodies. We propose that these structures in vent shrimps may fulfill functions in addition to higher order sensory processing and suggest a role in place memory. Our study promotes vent shrimps as fascinating models to gain insights into sensory adaptations to peculiar environmental conditions, and the evolutionary transformation of specific brain areas in Crustacea.