Kamio, M., Furukawa, D., Wakabayashi, K., Hiei, K., Yano, H., Sato, H., Yoshie-Stark, Y., Akiba, T., Tanaka, Y., (2015). Grooming behavior by elongated third maxillipeds of phyllosoma larvae of the smooth fan lobster riding on jellyfishes. Journal of Experimental Marine Biology and Ecology. 463: 115-124. doi: http://dx.doi.org/10.1016/j.jembe.2014.11.008
Meet the swashbucklin’ lobster larvae that rides its mighty jelly steed across the wild western Pacific and western Indian Ocean. This multi-limbed, transparent creature is known as the jellyfish rider. More specifically, it is the larvae of the smooth fan lobster or Ibacus novemdentatus (Image 1). Smooth fan lobsters are not true lobsters, but belong to the slipper lobster family. Despite their name, they wouldn’t make good house slippers–true story. During their larval stage, they have a flat body, and are dubbed ‘phyllosoma’ from the Greek ‘phyllo’, meaning leaf. Like other larvae of the slipper lobster family, jellyfish riders spend part of their days riding jellyfish, including moon jellies (Aurelia aurita), and get this—they also eat jellyfish. And yes—they will eat the very same jellyfish they ride, starting with the venomous tentacles. The advantages of having a single vehicle for transportation and food are obvious—it allows the phyllosoma to drift, rest and eat at its own convenience. Boat made of cheese, anyone?
While it seems like a good life, phyllosoma need to deal with mucus, a jellyfish’s chemical defense. Phyllosoma are also exposed to many different foulants (organisms or substances that attach to or cover the body) such as bacteria, fungi, parasites and debris. While all crustaceans moult their exoskeletons, foulants can impair appearance, movement and health in between moults. Grooming is therefore an important behaviour that prevents foulant buildup.
Crustaceans have developed a pair of unique mouth-related appendages called the third maxillipeds (M3) that they use for handling food and grooming (Image 2). The function of M3 is not well studied in slipper lobsters and grooming behaviours of phyllosoma are also not well documented due to the difficulties of obtaining and rearing a sufficient sample size. In a thorough and detailed study, Kamio, Furukawa, Wakabayashi et al., (2015) studied the function of this appendage. There were many components of the study that tackled a variety of questions, so try your best to follow along!
Smooth fan lobsters with eggs were purchased and raised to hatch out the phyllosoma.
Part #1: M3 length to body length ratio was measured in phyllosoma ranging from those that had just hatched to those that had completed 4 moults. The shape of M3 tips were then imaged under a stereomicroscope.
Part #2: Behavioural movements of M3 were recorded on video and then analyzed. Phyllosoma that had undergone 2-6 moults were used. To keep the phyllosoma in focus, one end of a grizzly bear hair was glued to the phyllosoma and the other end was attached to an anchor through a platinum wire.
Part #3: Stained gel was used as an artificial foulant and plotted on different parts of the body. Behaviour of the phyllosoma was then recorded and analyzed for 60 seconds after an acclimation period.
Part #4: Two groups of phyllysoma were exposed to foulants for seven days. One group had a tube glued around M3 to prevent effective grooming. The other control group had the same amount of glue placed on their carapace (see Ca in Image 2). Phyllosoma that had moulted six times were used because this procedure was harder to complete on smaller ones. Cyanobacteria, a type of foulant, were then counted under a microscope.
Step #5: A process which identifies and measures amounts of organic compounds called NMR (nuclear magnetic resonance) analysis, was applied to a solution composed partly of freeze-dried moon jellies. Glycine was identified as a key odour and extracted. Sponges that were either a) soaked with seawater as a control, or b) soaked with seawater and various concentrations of extracted glycine, were presented to the phyllosoma for 5 minutes and observed.
Results & Discussion
Result #1: M3 measured on phyllosoma were longer than the body at a ratio of 1.12 – 1.18 meaning that the appendages have the capacity to reach all parts of the body. The imaged structure (Image 3) of the M3 tips revealed a flexible, comb like shape, useful for wiping swaths of mucus and other unwanted pests, while the pereiopods (see P1-P5 in Image 2) had hard, sharp spines, perfect for clutching jellyfish.
Result #2: When not eating, larvae spent 50% of their time grooming with M3 and did not touch food with M3. When eating, M3 were pointed back away from the face to keep them out of the way. See video below for an original research recording!
Result #3: 80-94% of the artificial foulant was removed by grooming, the majority of the removal was done by M3, especially on the top of the back where no other appendage could reach.
Result #4: Cyanobacteria growth on phyllosoma that had constrained M3 was significantly higher at 20-40 spots than the control at 0-4 spots (Image 4).
Result #5: Sponges with higher concentrations of glycine were frequently grabbed, suggesting that glycine stimulates grooming and eating behaviour. In the absence of glycine, phyllosoma only spent 0.1% of the observed period grooming. Time spent grooming in the presence of glycine was significantly higher. See below for an original research recording!
Phyllosoma are planktonic, meaning they drift along with ocean currents before settling down on the sea floor to transform into hard-shelled adults. As drifting organisms that cannot bury or gain exposure to air to rid themselves of a diversity of foulants including swaths of defiant jellyfish mucus, they have something even better built in house. After a thoughtful set of tests and results, Kamio, et al., have strong evidence that phyllosoma have adapted specialized grooming appendages that function as body wipers to effectively squeegee off any unwanted hitchhikers.
(Special thanks to Michiya Kamio for providing research photos and videos and to Kei Nomiyama for permission to use featured image).