Most squid capture prey by extending two tentacles swiftly in front of them, then grabbing prey with suckers and/or hooks present on the tentacle clubs. Grimalditeuthis bonplandi is an unusual deep-sea squid because it lacks any tentacle club armature. How this poorly known squid captures prey has long puzzled scientists.
Dr Hendrik-Jan Hoving from the Monterey Bay Aquarium Research Institute (MBARI) in California and his team present the first observations of this squid in its natural environment. Using remotely operated vehicles (ROVs), specimens were observed wiggling the tentacle clubs in a way that resembles the movements of a smaller animal, suggesting that the tentacle club is used to lure prey close enough for capture.
Although cephalopods living between 200-4000m deep are diverse and widespread, their natural behaviour and lifestyle are known principally from observations of dead individuals that often have been unintentionally damaged by the nets that collected them. The use of ROVs and manned submersibles has allowed observations of rarely seen deep-sea squids alive in their natural habitat.
The scientists unexpectedly observed that G. bonplandi is unable to rapidly extend and retract the tentacle stalk as do other squids, but instead manoeuvres the tentacles by undulation and flapping of the clubs’ protective membranes. These tentacle club movements superficially resemble the movements of small marine organisms, suggesting the possibility that G. bonplandi uses aggressive mimicry by the tentacle clubs to lure prey, which consist of crustaceans and cephalopods.
In the deep-sea darkness, the flapping and undulatory movements of the tentacles may have a number of effects: (i) stimulating bioluminescence in the surrounding water, (ii) creating low-frequency vibrations and/or (iii) producing a hydrodynamic wake. Potential prey of G. bonplandi may be attracted to one or more of these signals.