The Squat Shrimp (Thor amboinensis) is a commensal shrimp associated with different anemones, corals, and even other crustaceans.
This little shrimp has a pantropical distribution and lives in the waters of the Indian, Pacific, and Atlantic Oceans. In the Atlantic Ocean, its habitat ranges from the Gulf of Mexico over the entire Caribbean region all the way to the Spanish islands of the Canaries on Africa’s northwestern coast. In the Indian Ocean, it is found from the warm waters of the Red Sea to the Indonesian archipelago and beyond, all the way to French Polynesia.
This very common shrimp, frequently encountered by scuba divers, has a caramel-coloured body and symmetrically white patches edged with thin electric blue lines, with a length of around 13mm/0.5inch. In some areas, they are more greenish in colour. They have a typical posture, with an always upwards-pointed tail. Their tail is also almost always moving up and down.
This commensal shrimp is found to congregate in little groups on a wide variety of hosts, including tube anemones, carpet anemones, adhesive anemones, mushroom corals, and even in the burrows of slashing mantis shrimp. They use the anemone as protection against possible predators.
Squat Shrimp or sometimes strangely called Sexy Shrimp are a favourite subject of underwater photographers and videographers. Their beautiful white markings in combination with their strange upward pose while sitting on their host makes them photogenic.
The Squat Shrimp feeds mainly on the mucus of its host and on small planktonic organisms trapped in the anemone’s tentacles. The mucus used to build the Slashing Mantis Shrimp hideaways and burrows, as well as the remains and leftovers of the mantis’ prey, is also a food source for the Squat Shrimp when it shares the mantis shrimp’s home.
The Squat Shrimp are protandrous hermaphrodites, beginning their lives as males. At a later stage in life, they become female. Females, who are always older than the males, are also about two times larger. After mating, the female carries the fertilised eggs under her abdomen. When the eggs hatch, the larvae are released into the water column.
Four identical shots, each taken from a different distance, bit by bit reveal more of the shrimp’s habitat, a technique that I use a lot.
To film the shrimp in more detail, I used a dioptre mounted over my standard dome. A macro lens or dioptre makes it possible for the underwater videographer to enlarge small subjects while filming underwater.
Squat Shrimps are easy to spot underwater. A good place to find them is in the direct vicinity of tube anemones and around carpet anemones but not amongst the tentacles of the anemone. When you spot a Slashing mantis Shrimp in its burrow, it is recommended to have a look inside the burrow, as most scuba divers tend to focus on the big and often impressive mantis, overlooking smaller critters like the Squat Shrimp that often share the same hideaway.
The music was chosen to match the frantic movement of the Threespot Dascyllus (Dascyllus trimaculatus) juveniles in the last shot.
For another in-depth description about Squat Shrimp living in a Slashing Mantis' burrow please go to our vlog post 32 or click on this link: https://www.beyondscuba.com/post/spearing-mantis-shrimp-lysiosquillidae
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