Ryan Photographic - Paguridae - Marine hermit crabs

 

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Family Paguridae

The World Register of Marine Species (WoRMS) lists 1006 species of hermit crab classified into 87 genera. However, as this entry hasn't been updated since 2011, these figures will no longer be accurate. In marked contrast, Wikipedia suggests there are 542 species in over 70 genera.

Hermit crabs are typically thought of as requiring molluscan shells for protection of their soft abdomens. While this is true for the majority, there are some species, such as the Paguritta hermits (shown below) which live in polychaete burrows or make their own in coral (but I have been unable to find out how they do this or how they ecdyse in such a situation). A few really "aberrant" species use flattened sea anemone species for protection and also do away with the shell. Until recently there was only one species known in this genus (first collected on the extraordinary HMS Challenger expedition). In 2018 Lemaitre et al. described 5 new species and erected a new genus. The crabs protect their abdomen with the anemone and are able to pull the aemone up over their carapace like a blanket. The anemones remain undescribed. Very cool.

Another fascinating hermit crab is the staghorn hermit crab. I was diving in the Sea of Cortez when I saw a staghorn coral walk across the sea floor. I checked my depth gauge to see if I could be "narked". Closer examination showed the presence of a crab. Ignoring the "look but don't touch" mantra of scuba divers, I turned the coral over and saw a cheliped blocking a chamber. Placed back upright the crab soon emerged and, it, and the coral, walked away. The crab initially has a mollusc shell upon which a hydrocoral larvae settles. As the coral grows it eventually absorbs the crab shell and a chamber forms in the coral. Bloody amazing stuff.

Other hermits, most notably Dardanus pedunculatus, decorate their shell with anemones, the prevailing wisdom is that this protects them from predators, particularly octopuses. This is a fascinating relationship. When the hermit needs to change shells it removes the anemones from its old shell and attaches them to the new one. Incredibly, the anemones seem to "know" what is happening and loosen their pedal disk from the shell when tapped by the crab.

 

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Dardanus guttatus, Blue-knee hermit crab

Dardanus guttatus, Blue-knee hermit crab, Taveuni, Fiji-4978

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Dardanus lagopodes Dark-knee hermit crab

Dardanus lagopodes Dark-knee hermit crab, Raja Ampat West Papua IMG_3336

Dardanus lagopodes Dark-knee hermit crab Kri Eco, Raja Ampat IMG_8196

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Dardanus megistos, White-spotted hermit crab

Dardanus megistos, White-spotted hermit crab Kri Eco, Raja Ampat, West Papua IMG_3886

Dardanus megistos, White-spotted hermit crab. Kri Eco, Raja Ampat, West Papua IMG_3887

Dardanus megistos, White-spotted hermit crab Puerto Galera, Philippines IMG_6048

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Dardanus pedunculatus, Anemone hermit crab

Dardanus pedunculatus, Anemone hermit crab, Kri Eco, Raja Ampat, West Papua IMG_0418

Dardanus pedunculatus, Kri, Raja Ampat, West Papua IMG_0419

Dardanus pedunculatus Anemone hermit crab Puerto galera, Philippines IMG_5955

Dardanus pedunculatus, anemone hermit crab eye detail, Raja Ampat, West Papua IMG_0423

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Dardanus venosus? starry- eyed hermit crab

Dardanus venosus? starry- eyed hermit crab, Glover's Reef, Belize - IMG_3413

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Manucomplanus varians, Staghorn hermit crab

Manucomplanus varians, Staghorn hermit crab inside hydrozoan Janaria mirabilis IMG_5708

Manucomplanus varians, Staghorn hermit crab inside hydrozoan Janaria mirabilis IMG_5706

Manucomplanus varians, Staghorn hermit crab and underside of hydrozoan Janaria mirabilis IMG_5969

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Paguritta corallicola Coral residing hermit crab

Paguritta corallicola Coral residing hermit crab Somosomo Strait IMG_3398

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Paguritta harmsi Coral hermit crab

Paguritta harmsi Coral hermit crab, Raja Ampat, West Papua IMG_4154

Paguritta harmsi Coral hermit crab, Raja Ampat, West Papua IMG_4158

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Paguritta sp. Coral hermit crab

Paguritta sp. Coral hermit crab, Fiji

Paguritta species Coral residing hermit crab Fiji 3. The finally divided antennae which filter food out of the water are clearly visible.

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Pagurus hirtimanus? Hairy hermit crab

Pagurus hirtimanus? Hairy hermit crab Raja Ampat IMG_9787

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Unidentified Blue-eyed hermit crab

Blue-eyed hermit crab, Sea of Cortez IMG_6337

Blue-eyed hermit crab, Sea of Cortez IMG_6388

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