Anatomy
of an Anemone Hermit Crab
To
learn more about Anemone Hermit Crabs, click here.
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Anemone
hermit crab, Dardanus brachyops, with sea anemone, Caliactis
armatus, caught in one of the deep set traps. This
particular animal also had a barnacle on its shell that
the taxonomists could not identify, and it may be a new
species.
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Anemone: Anemone hermits often have more than one anemone
on their shell, as well as more than one species of anemone that they are
associated with. This specimen took the prize for the most anemones. |
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Stinging Threads: The pink threads (acontia) in the image are composed of stinging cells, and the anemone ejects them for defense when it is threatened or stressed. These threads extend far beyond the anemone and may provide longer distance defense than the stinging cells in the tentacles themselves.
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Legs for Grabbing Shell: The
hermit’s last pair of legs are adapted for grabbing holding onto the inside
of the shell. Photo: Joel Martin |
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Eyes and Hairs: Hermit crabs have eyes that are on stalks so they can see beyond the edge of their shell. The legs and body are also covered with short hairs that are chemosensory (smell) or tactile (they can feel, or sense movement in the water).
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Other Associated Species: In addition to anemones, other species such as worms and amphipods are associated with anemone hermit crabs. One crab we found had a barnacle, worm casings and anemones attached to its shell. This presents a particularly interesting evolutionary question of how these associations developed over time, and what the advantages are.
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Oversize Front Claw: Most hermit crabs have uneven front legs adapted as strong pincers. Usually one claw is larger than the other and doubles as a strong claw for feeding and defense, and also to close the opening of the shell when the hermit retreats inside it.
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*All images and information from French Frigate Shoals are provided
courtesy of the Northwestern Hawaiian Islands Marine National Monument,
Hawaiian Islands National Wildlife Refuge, the Northwestern Hawaiian
Islands State Marine Refuge, and NOAA's Pacific Islands Fisheries
Science Center in accordance with permit numbers NWHIMNM-2006-015,
2006-01, 2006-017, and DLNR.NWHI06R021 and associated amendments.
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