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Phylum Arthropoda > Subphylum Crustacea > Class Malacostraca > Order Decapoda > Anomurans
Hermit crabs
Infraorder Anomura
updated Jan 2020

if you learn only 3 things about them ...
They belong in their shells. Don't try to remove them!
Every empty shell is a potential hermit crab home. Don't take any shells home!
Many other animals may live together with a hermit crab. Don't take hermits home!

Where seen? Hermit crabs are commonly seen on many of our shores. They come in all sizes from tiny to large, and live in all kinds of shells. The same kind of hermit crab may live in different kinds of empty shells. Hermit crabs may live even in broken shells.

What are hermit crabs? Hermit crabs belong a subgroup called Anomurans in the Order Decapoda. Anomurans includes porcelain crabs. These crab-like animals are not true crabs. True crabs belong to a subgroup called Brachyurans within the Order Decapoda.


Features: True crabs have a hard, shortened abdomen which they fold under their hard shells for protection. Hermit crabs, on the other hand, have a soft, long abdomen. They have to insert this abdomen into an empty shell for protection. The soft abdomen is twisted to one side for a better fit into the spiral of a shell. There are appendages at the end of the abdomen to hang on tight to the shell.

Unlike true crabs, hermit crabs have only two pairs of walking legs. They have eyes on long stalks to peek out of the shell. Their antennae may be very long, or feathery. Like true crabs, hermit crabs have two pincers. Both are used to feed with, and usually one is used to block the shell entrance when the hermit crabs retreats into its shell. This makes it more difficult for predators to pry them out of their shells. In some species, one of the pincers is much larger than the other.

Changi, May 11

This hermit crab is using a half broken shell.

Small 'legs' on the abdomen cling to the shell.
Empty shells are priceless! Hermit crabs need empty shells to protect themselves, so please don't take any shells home with you. Hermit crabs need them more than you do! They will die without empty shells.

Hermits belong in their shells:
Please don't try to pull hermit crabs out of their shells. You may rip out their little appendages or tear their delicate abdomens.

What it looks like inside the shell!

The same kind of hermit crab can live
in a wide variety of shells.

Chek Jawa Feb 07

Even a broken shell can be a hermit home.
Tanah Merah, Jun 09
House hunting: As a hermit crab grows bigger, it has to find a bigger shell. A shell that is too small provides less effective protection from predators as the hermit crabs can't retreat deep into the shell. Hermit crabs understood the concept of 'upgrading' long before other Singaporeans!

Before switching shells, a hermit crab will tentatively test out the new shell first, while holding on to the old one. If the new shell is not ideal, it instantly goes back into the old shell. A hermit crab does not necessarily always use the same kind of shell.

Hermit crabs never kill the original occupant of the shell. They may, however, quarrel with other hermit crabs over a desirable shell. Every shell is a potential hermit crab home. Even a tiny broken shell or an ugly shell covered with barnacles. One of the factors limiting the population of hermit crabs is the availability of suitable empty shells. So please don't take any shells away from our shores. More about hermit crabs moving into a new shell on the wild shores of singapore blog.

Land hermit crabs may even live
in land snail shells!

St. John's Island, Jun 07


Hanging onto the shell of a snail so recently dead that whelks are still cleaning it out!
Tanah Merah, Feb 07

Even tiny Button shells are homes
to tiny hermit crabs.
Changi, Apr 05
Living with a hermit: The hermit crab makes such a comfy home in its borrowed shell that other animals take up residence with it. These include the Slipper snail (Family Crepidulidae), tiny porcelain crabs and sea anemones. These animals enjoy the constant flow of oxygenated water that the hermit crab generates, snack on the hermit crab's leftovers, and the hermit crab will hide in the sand or crevices where its safe and wet so the hitch-hikers don't risk drying out.

Tiny sea anemones may be found on
a shell occupied by a hermit crab.
Changi, Apr 07

Others may have big sea anemones!
Changi, Apr 07

Slipper snails are often found on the inside of the shell occupied by a hermit crab.
Changi, Apr 05

Tiny porcelain crabs
Changi, Apr 05

Keelworms may build their tubes on the shell.
Changi, Jun 05

Little animals also bore into the shell,
possibly boring sponges.
Changi, Aug 08

Scale worms are sometimes seen on the shell.
Changi, Aug 08

Unknown animal on the shell.
Changi, Aug 08

Slipper snails and keelworms
Changi, Jun 05
What do they eat? Many hermit crabs are scavengers. These have a keen sense of smell to find their food. Others eat algae and detritus.

Hermit babies: Hermit crabs have separate genders. To mate, hermits crabs partially emerge from their shells, releasing eggs and sperm simultaneously. The eggs hatch into free-swimming larvae that drift with the plankton before eventually settling down and developing into tiny hermit crabs. Some hermit crab females may brood their eggs inside their shells.


Hermit crabs belong on the seashore!
Please don't take hermit crabs home. And please don't buy one from a pet store. Hermit crabs sold in a pet store are collected from the wild. Many have died during the collection process, before they are even sold. And many of those sold also eventually die from neglect or ignorance of proper care. For example, within the confinement of a small tank, most die during a moult. In the wild, they are able to find the correct place to moult, with the proper high humidity. More about moulting.

Moult outside the shell,
original hermit crab inside the shell?
Changi, Jul 05

Transparent eyes indicates this is a moult.

Hermit crab tracks on sand.
Chek Jawa, Jan 04
Even if they are kept alive for a long time, hermit crabs removed from the habitat generally do not reproduce successfully. Thus, they do not contribute to the wild population. Other animals rely on hermit crabs as homes and as food. Removing wild hermit crabs hurts the ecosystem.

If you have bought a pet hermit crab and now feel bad about keeping it, please do not release it on our shores. It may not be the same species as those naturally found on our shores. It may have diseases that may be passed on to our marine life. The least worst option would be to return it to the pet shop where you bought it from. If you enjoy looking at hermit crabs, why not visit them on the shore and observe them in their natural surroundings doing what hermit crabs do?

Just moulted.
Tuas, Sep 11

Moult with transparent eyes.
Tuas, Sep 11
Special hermits: Land hermit crabs belong to the Family Coenobitidae which includes the largest hermit crab: the Robber or Coconut crab (Birgus latro). The Robber crab is so large that it no longer needs to live in an empty snail shell for protection. The Robber crab is only found in the Indian and Pacific Ocean islands. It is not found in Singapore.

Role in the ecosystem: Hermit crabs are eaten by many animals higher up in the food chain. Bigger crabs and birds can pry them out of their shells to eat them. Many small animals live with hermit crabs (see above). Many hermit crabs are scavengers and help quickly recycle dead matter on the shores.


Status and threats: The Land hermit crabs (Coenobita sp.) are listed as 'Vulnerable' on the Red List of threatened animals of Singapore due to loss of our natural beaches. As for our other hermit crabs, like other creatures of the intertidal zone, they are affected by human activities such as reclamation and pollution as well as over-collection for the pet trade and by hobbyists.

Some Hermit crabs on Singapore shores


 




Hermit crabs recorded for Singapore
from Dwi Listyo Rahayu, 2000. Hermit crabs from the South China Sea (Crustacea: Decapoda: Anomura: Diogenidae, Paguridae, Parapaguridae)
in red are those listed among the threatened animals of Singapore from Davison, G.W. H. and P. K. L. Ng and Ho Hua Chew, 2008. The Singapore Red Data Book: Threatened plants and animals of Singapore.
*from Lim, S., P. Ng, L. Tan, & W. Y. Chin, 1994. Rhythm of the Sea: The Life and Times of Labrador Beach.
**from WORMS
+Other additions (Singapore Biodiversity Records, etc)
++from The Biodiversity of Singapore, Lee Kong Chian Natural History Museum.

  Hermit crabs seen awaiting identification
Species are difficult to positively identify without close examination.
On this website, they are grouped by external features for convenience of display.
 
  Huddling hermit crab
Lavender hermit crab

  Family Coenobitidae (Land hermit crabs) with list of species recorded for Singapore

  Family Diogenidae
  Clibanarius spp.
Clibanarius clibanarius
Clibanarius cruentatus
(Gold-spotted hermit crab)
*Clibanarius infraspinatus (Orange-striped hermit crab)
*Clibanarius longitarsus (Blue-striped hermit crab)
Clibanarius merguiensis
Clibanarius padavensis
Clibanarius serenei
Clibanarius striolatus
+Clibanarius sp. (All-black hermit crab)
+Clibanarius sp. (Tawny hermit crab)

Dardanus callichela
Dardanus gemmatus
Dardanus hessii

+Dardanus lagopodes (Very hairy hermit crab)
Dardanus megistos (Orange spotted hermit crab)
Dardanus setifer

*Diogenes sp. (Tidal hermit crab)
*Diogenes avarus (Common tidal hermit crab)
Diogenes custos
Diogenes diogenes
Diogenes edwardsii
Diogenes fasciatus
++Diogenes foresti
Diogenes inglei
+Diogenes klaasi
++Diogenes jousseaumei
Diogenes jubatus
Diogenes lophochir
Diogenes mixtus
+Diogenes moosai
Diogenes pallescens
Diogenes platyops=**Diogenes jubatus
+Diogenes singaporensis
Diogenes stenops=**Diogenes jousseaumei
Diogenes tumidus

Paguristes longirostris (Blue-elbowed hermit crab)

+Pseudopaguristes monoporus ('Blue-orange' banded hermit crab)

  **Family Paguridae (previously in Family Diogenidae)
  +Pagurus hedleyi (Pink banded hermit crab)
Pagurus kulkarnii
+Pagurus pitagsaleei

Spiropagurus spiriger

Links

References

  • D. L. Rahayu, H.-T. Shih & P. K. L. Ng. 29 June 2016. A new species of land hermit crab in the genus Coenobita Latreille, 1829 from Singapore, Malaysia and Indonesia, previously confused with C. cavipes Stimpson, 1858 (Crustacea: Decapoda: Anomura: Coenobitidae). The Raffles Bulletin of Zoology 2016 Supplement No. 34 (Part I of II) Pp. 470-488.
  • Dwi Listyo Rahayu & Rene Ong. 2 October 2015. Rediscovery of the hermit crab, Dardanus hessii, in Singapore. Singapore Biodiversity Records 2015: 145-147
  • D. L. Rahayu. New record and new species of the hermit crab genus Diogenes Dana, 1851 (Decapoda: Anomura: Diogenidae) from Singapore. 10 July 2015. The Comprehensive Marine Biodiversity Survey: Johor Straits International Workshop (2012) The Raffles Bulletin of Zoology 2015 Supplement No. 31, Pp. 182-192.
  • Dwi Listyo Rahayu, 2000. Hermit crabs from the South China Sea (Crustacea: Decapoda: Anomura: Diogenidae, Paguridae, Parapaguridae) (pdf). The Raffles Bulletin of Zoology 2000 Supplement No. 8: 377-404. The National University of Singapore.
  • Dwi Listyo Rahayu, 1996. Notes on littoral hermit crabs (Excluding Coenobitidae) (Crustacea: Decapoda: Anomura) mainly from Singapore and Peninsular Malaysia (pdf). The Raffles Bulletin of Zoology 1996 44(2): 335-355
  • Davison, G.W. H. and P. K. L. Ng and Ho Hua Chew, 2008. The Singapore Red Data Book: Threatened plants and animals of Singapore. Nature Society (Singapore). 285 pp.
  • Lim, S., P. Ng, L. Tan, & W. Y. Chin, 1994. Rhythm of the Sea: The Life and Times of Labrador Beach. Division of Biology, School of Science, Nanyang Technological University & Department of Zoology, the National University of Singapore. 160 pp.
  • Chuang, S. H., 1961. On Malayan Shores. Muwu Shosa, Singapore. 225 pp., plates 1-112.
  • Jones Diana S. and Gary J. Morgan, 2002. A Field Guide to Crustaceans of Australian Waters. Reed New Holland. 224 pp.
  • Debelius, Helmut, 2001. Crustacea Guide of the World: Atlantic Ocean, Indian Ocean, Pacific Ocean IKAN-Unterwasserachiv, Frankfurt. 321 pp.
  • Davey, Keith, 1998. A Photographic Guide to Seashore Life of Australia. New Holland, Australia.144 pp.
  • Edward E. Ruppert, Richard S. Fox, Robert D. Barnes. 2004.Invertebrate Zoology Brooks/Cole of Thomson Learning Inc., 7th Edition. pp. 963.
  • Pechenik, Jan A., 2005. Biology of the Invertebrates. 5th edition. McGraw-Hill Book Co., Singapore. 578 pp.
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