Subject: Spearing Mantis Shrimps (Lysiosquillidae) have excellent and advanced eyesight. Their vertically elongated eyes can move independently of each other and are mounted on mobile stalks. These strange marine critters can perceive wavelengths of light ranging from deep ultraviolet to far-red and polarised light. Therefore, they are able to recognise different types of coral, well-camouflaged and/or almost transparent prey, and easily detect predators that might have iridescent and shiny scales such as barracudas. It is believed that these crustaceans have the best and most advanced eyesight in the entire animal kingdom.
Each compound eye is made up of tens of thousands of ommatidia. These clusters of photoreceptor cells look like little mirrors. When these crustaceans move their eyes, it results in a mesmerising image, a little bit like a moving disco mirror ball hanging on the ceiling of a nightclub. A cool feature to catch on video or photo.
Despite their name, these animals are not real shrimp but Stomatapods (shrimp have 5 pairs of walking legs, Stomatapods have only 3 pairs). There are around 450 different species of Mantis Shrimp spread over 4 main groups determined by the type of claws they possess; smashers, spearers, hatchet, and spike smashers. These claws are, in some species, calcified 'clubs' or “bats” that can strike with great power, while others, like the group of the spearers, have sharp forelimbs used to seize the prey (hence their common name "mantis," named after the Praying Mantis insects).
Spearers, such as the one in this video, are armed with spiny appendages - the spines having barbed tips - used to stab and snag prey. They strike by rapidly unfolding and swinging their raptorial claws at the prey and can inflict serious damage on victims significantly greater in size than themselves.
They make a U-shaped burrow in the sand that can be up to 5m/15ft long and 12cm/5in in diameter, which they use as sites for retreat and as locations for consuming their prey. The large amount of mucus used to build these hideaways, as well as the remains and leftovers of their prey, attracts smaller cleaners and scavengers like Squat Shrimps (Thor amboinensis), as shown here in this footage. These small shrimps usually form symbiotic relationships with anemones, where they feed on plankton trapped in a host anemone's mucus.
Because it is impossible to see the whole animal it was impossible to identify the exact species in this videoclip.
Technique: These big critters are seldom seen outside of their burrows. Because they are not moving around, they are easy to film. However, when suddenly overwhelmed by the appearance of a diver, a camera, and video lights, they can retreat into their hideaway for quite a long time. It can be a real waiting game to film these beautiful crustaceans. This waiting game can be used by the underwater videographer or photographer to get the camera settings right and move the video lights into a nearly perfect position to get great footage of this intriguing animal. Patience is always key in underwater videography. Sounds were added to the clip during the editing process to make the watching experience more real.
For another in-depth description about Squat Shrimp please go to our vlog post 32 or click on this link: https://www.beyondscuba.com/post/the-squat-shrimp-thor-amboinensis-1
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