Biology

Articles and documents regarding the biology of hermit crabs.

Hermit crab grooming

Coenobita perlatus grooming itself - Photo by Stacy Spangler of Isopod Connection

Coenobita perlatus grooming itself – Photo by Stacy Spangler of Isopod Connection

In hermit crabs, the fourth and particularly the fifth pereopods are reduced, usually remaining within the confines of the gastropod shell and hence are not used for walking. These appendages do however becoming important when the hermit crab attempts to right itself, providing anchorage within the shell. Further, the fifth pereopod has become specialised as a gill cleaning appendage, often resting within the gill chamber (Bauer 1981). On the abdomen only the left pleopods are retained (Poore 2004).[1]

Hermit crabs used specialized setae on the third maixillipedes and fifth pereiopods for most grooming but used the unmodified first, second, and third pereiopods as well. Most brachyuran grooming was performed with modified setae on the the third maxillipedal palps and eipods, with a row of simple setae on each chelipede merus, and with the chelipede fingers.

The third maxillipedes and fifth pereiopods performed the majority of movements, including all of the more complex actions, and were suprisingly dexterous. Coenobita clypeatus devoted most of it’s grooming energy on the eyes and anntennules and did so with the mesial surfaces of the dactylus, propodus, carpus, and distal merus of the third maxillipedal endopods.

The three pairs of walking legs (chelipedes included) groomed themselves by scrubbing against each other in various combinations of two or three appendages. In addition, the fingers of the minor chelipede picked at the surface of the major chelipede. The chelate fifth pereiopods were quite flexible and extended as far forward as the chelipedes. The fifth pereiopods also groomed most of the central and posterior carapace, including the branchial chamber, and much of the abdomen. The fifth peeriopods groomed much of the shell’s interior, particularly the columella and innner and outer lips, as well as the exterior lips.These appendages did not function exclusively as grooming organs, as they also use their laterally situated gripping scales to brace the body against the shell (Johnson 1965, Vuillemin 1970).

After every few grooming acts, the fifth pereiopods moved anteriorly, in unison. to meet the two third maxillipedes, which were extended posteriorly beneath the body. The plumodenticulate and serrate setai of the posterior appendages were then scrubbed by the maxillipedes. The third maxillipedes, in turn, were scrubbed against each other and/or against the second maxillipedes after a grooming bout. The interior mouthparts had a self-cleaning function as well.

Thus, the maxillipedes groomed the anterior portion of the body (especially the sensory structures), the walking legs groomed each other, and the fifth pereiopods scrubbed the most posterior areas. Two movements were, at times, performed simulanteously, e.g., mutual leg scrubs and anntennule grooming. Although grooming may occur at any time, it was most frequentl and intense immediately after a ran and was often performed in standing water if it was available. Water is clearly an important debris-flushing medium. The grooming setae, parrticuarly the serrate setae, may also serve in a sensory capacity (Derby 1982).

Foam bathing, in which bubbles produced by the mouthparts disperse fluid about the body, occurred in partially submerged or emergent crabs. This action has been variously interpreted as a method of thermoregulation, pheromone distribution, water reserve aeration, or cleansing (Altevogt 1968, Wright 1966, Lindberg 1980, Jacoby 1981, Schone & Schone 1963, Brownscombe 1965). [2]

References
Dardanus megistos by Storm Martin 2012
2. Grooming structure and function in some terrestrial Crustacea

Coenobita Gonopore

Gonpores are the openings of reproductive system to exterior. In male, pore on basal segment (coxa) of last (eighth) thoracopods; in female, pore on coxa of sixth thoracopods (third pereopods) [1]

Coenobita rugosus has been found to be intersexual

Location of gonopores in male and female Coenobita

Location of gonopores in male and female Coenobita

 

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Overview of the anatomy of a land hermit crab (Coenobita)

References:
1 Stachowitsch, 1992

Coenobita Shield

The Cephalic shield [1] or carapace is part of the exoskeleton that covers the cephalothorax. It functions as a protective cover, hence the common name ‘shield’.

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Overview of the anatomy of a land hermit crab (Coenobita)

Photo credits:
HUSO Chen Yu-Jung

Stacy Griffith

References:

  1. Dardanus megistos by Storm Martin 2012

Coenobita Antennae

Land hermit crabs have two pairs of antennae. The antennae are vital sensory organs that allow Coenobita to locate the ocean, their food and to explore their surroundings. Coenobita rely on humidity in the air to aid them in smelling and locating various odors. In Coenobita Violascens the antennal acicle is fused with second peduncular segment. To capture odors, crustaceans move their antennules back and forth through the water in a motion called flicking.

Hermit Crab Antenna Eyes Diagram by Storm Martin 2012

Hermit Crab Antenna Eyes Diagram by Storm Martin 2012

We are building image galleries of specific body parts. If you have high resolution, clear photos that you would like to donate to this project please contact us via email: crabstreetjournal at gmail dot com


Overview of the anatomy of a land hermit crab (Coenobita)

Photo Credits:
The Crab Street Journal has been granted permission by these photographers to use their photo(s) on our site.
Glen R
Mount Gao

Coenobita chela and cheliped

Chela (organ)

A chela /kˈiːlə/, also named claw, nipper or pincer, is a pincer-like organ terminating certain limbs of some arthropods.[1] The name comes from Greek (χηλή) through New Latin (chela). The plural form is chelae.[2] Legs bearing a chela are called chelipeds.[3] Another name is claw because most chelae are curved and have a sharp point like a claw.

Also called pincer or pincher.

We are building image galleries of specific body parts. If you have high resolution, clear photos that you would like to donate to this project please contact us via email: crabstreetjournal at gmail dot com


Overview of the anatomy of a land hermit crab (Coenobita)

Photo Credits:
The Crab Street Journal has been granted permission by these photographers to use their photo(s) on our site.

References
1 Dean Pentcheff. “Chela”. Crustacea glossary. Natural History Museum of Los Angeles County. Retrieved November 28, 2011.
2 George Gordh, Gordon Gordh & David Headrick (2003). A Dictionary of Entomology. CAB International. p. 182. ISBN 978-0-85199-655-4.
3 Dean Pentcheff. “Cheliped“. Crustacea glossary. Natural History Museum of Los Angeles County. Retrieved November 28, 2011.

Coenobita eyes

Coenobita possess compound eyes comprised of faceted lenses which are especially adept at picking up fine movements. The eyes are located on movable stalks and this is one of the primary ways we determine the species of hermit crab we are looking at.

Reconstructed brains of Fuxianhuia protensa and land hermit crab Coenobita clypeatus showing homologies with Malacostraca. They share 3 nested neuropils in each eye stalk (arrowed 1-3), A1n (antennal nerve), A2n (second pair of nerve roots), op t (optic tract).

Reconstructed brains of Fuxianhuia protensa and land hermit crab Coenobita clypeatus showing homologies with Malacostraca. They share 3 nested neuropils in each eye stalk (arrowed 1-3), A1n (antennal nerve), A2n (second pair of nerve roots), op t (optic tract).

 

Hermit Crab Antenna Eyes Diagram by Storm Martin 2012

Hermit Crab Antenna Eyes Diagram by Storm Martin 2012

 

We are building image galleries of specific body parts. If you have high resolution, clear photos that you would like to donate to this project please contact us via email: crabstreetjournal at gmail dot com

Overview of the anatomy of a land hermit crab (Coenobita)

Photo Credits:
The Crab Street Journal has been granted permission by these photographers to use their photo(s) on our site.
Sean Carroll

Heather Heaton

Stacy Griffith

Coenobita Gills

The gills of Coenobita and Birgus are modified for air-breathing but are reduced in number and size and have a comparatively small surface area. The branchiostegal lungs of Coenobita (which live in gastropod shells) are very small but are well vascularized and have a thin blood/gas barrier. Coenobita has developed a third respiratory organ, the abdominal lung, that is formed from highly vascularized patches of very thin and intensely-folded dorsal integument. Oxygenated blood from this respiratory surface is returned to the pericardial sinus via the gills (in parallel to the branchiostegal circulation). Birgus, which does not inhabit a gastropod shell, has developed a highly complex branchiostegal lung that is expanded laterally and evaginated to increase surface area. The blood/gas diffusion distance is short and oxygenated blood is returned directly to the pericardium via pulmonary veins. We conclude that the presence of a protective mollusc shell in the terrestrial hermit crabs has favoured the evolution of an abdominal lung and in its absence a branchiostegal lung has been developed. [1]

We are building image galleries of specific body parts. If you have high resolution, clear photos that you would like to donate to this project please contact us via email: crabstreetjournal at gmail dot com


Overview of the anatomy of a land hermit crab (Coenobita)

References:
1 The morphology and vasculature of the respiratory organs of terrestrial hermit crabs (Coenobita and Birgus): gills, branchiostegal lungs and abdominal lungs
C.A. Farrellya, P. Greenawayb, ,
a 32 Tramway Pde. Beaumaris, Vic. 3193, Australia
b School of Biological, Earth and Environmental Sciences, University of New South Wales, Sydney, N.S.W. 2052, Australia

Coenobita molt sac

The land hermit crab (Coenobita) develops a water sac inside of their shell prior to a molt. As shedding of the old exoskeleton begins, this store of water is used to expand the body to stretch and increase size before the soft exoskeleton begins to harden again

We are building image galleries of specific body parts. If you have high resolution, clear photos that you would like to donate to this project please contact us via email: crabstreetjournal at gmail dot com


Overview of the anatomy of a land hermit crab (Coenobita)

Coenobita mandibles and maxillipeds

The mandible (from Latin: mandibula or mandĭbŭ-lum, a jaw) [1] of an arthropod is a pair of mouthparts used for either for biting, cutting and holding food. The last three cephalic segments, together with the three most anterior thoracic segments (all of the cephalothorax), house the external mouthparts. From anterior to posterior these are the mandibles, maxillules, maxillae and then the three pairs of thoracic maxillipeds. These are all biramous except for the mandibles and maxillules. [2] Mandibles are often simply referred to as jaws. Maxillipeds are appendages modified to function as mouthparts.  Hermit crabs are often seen grooming their eyes with their maxillipeds much like a cat uses it’s paw to clean its face.

We are building image galleries of specific body parts. If you have high resolution, clear photos that you would like to donate to this project please contact us via email: crabstreetjournal at gmail dot com


Overview of the anatomy of a land hermit crab (Coenobita)

Photo Credits:
The Crab Street Journal has been granted permission by these photographers to use their photo(s) on our site.
Chen Yu-Jung

References:
1 Latin Dictionary Founded on Andrews’ edition of Freund’s Latin dictionary revised by Charlton T. Lewis, Ph.D. and. Charles Short, LL.D. Oxford. Clarendon Press. 1879.

2. Dardanus megistos by Storm Martin 2012

Coenobita gravid

grav·id: ˈɡravid/ adjective 1. pregnant; carrying eggs or young.

Land hermit crabs carry their brood inside of the shell until they are ready to be released into the ocean.

Gravid Coenobita purpureus Credit Felix Wang

Gravid Coenobita purpureus Credit Felix Wang

We are building image galleries of specific body parts. If you have high resolution, clear photos that you would like to donate to this project please contact us via email: crabstreetjournal at gmail dot com


Overview of the anatomy of a land hermit crab (Coenobita)