Ghost crab
Ghost crabs | |
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Horned ghost crab ( | |
Scientific classification | |
Domain: | Eukaryota |
Kingdom: | Animalia |
Phylum: | Arthropoda |
Class: | Malacostraca |
Order: | Decapoda |
Suborder: | Pleocyemata |
Infraorder: | Brachyura |
Family: | Ocypodidae |
Subfamily: | Ocypodinae Rafinesque, 1815 |
Type genus | |
Ocypode Weber, 1795
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Genera
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Ghost crabs are semiterrestrial
Characteristics of the subfamily include one claw being larger than the other, thick and elongated eyestalks, and a box-like body. The differences in claw sizes, however, are not as marked as in male
Taxonomy
Ocypodinae is one of two
Ocypodinae was previously regarded as
Genera
The subfamily Ocypodinae currently contains 22 species in these two genera:[5]
Description
Most ghost crabs have pale-colored bodies that blend in well with the sand,[3] though they are capable of gradually changing body coloration to match their environments and the time of day.[6][7] Some species are brightly colored, such as Ocypode gaudichaudii and Ocypode ryderi.[2][5]
Ghost crabs have elongated and swollen eyestalks with very large corneas on the bottom half. Their carapaces are deep and box-like, squarish when viewed from the top with straight or slightly curving sides. The regions of the carapace are usually not clearly defined. The "whip" of their
Ghost crab species can be most reliably identified by means of the area where they were recovered, the presence of "horns" (styles) on their eyestalks (exophthalmy), the pattern of stridulating (sound-producing) ridges on the inside surface of the palms of their larger claws, and the shape of the gonopods in males.[5]
Exophthalmy is exhibited by seven species in the subfamily:
Stridulating ridges also differ from species to species, with some displaying rows of tubercles, others displaying rows of smaller ridges (striae), or a combination of both. These are very important in identifying species as they are displayed by both adults and juveniles (though they may be absent in newly regenerated claws). They are used by ghost crabs for communication.[5]
Both exophthalmy and stridulating ridges, however, can not be reliably used to determine
Ecology
Ghost crabs dig deep burrows near the intertidal zone of open sandy beaches. The burrows are usually composed of a long shaft with a chamber at the end, occasionally with a second entrance shaft.[1] They are semi-terrestrial and breathe oxygen from the air through moistened gills. They must periodically wet their gills with seawater,[1][9] usually by taking water from moist sand or by running into the surf and letting the waves wash over them. However, they can only remain under water for a limited amount of time, as they will drown.[10][11]
Ghost crabs are
Ghost crabs are swift runners, darting away at the slightest sign of danger. They either head back to their burrows or into the sea to escape intruders.[10][11][13] The gaits of ghost crabs alter as their speed increases. Observations on O. ceratophthalma show it can walk indefinitely using all four pairs of walking legs, occasionally alternating which side leads. At higher speeds, the fourth pair of legs is raised off the ground, and at the highest speeds, the crab runs, using only the first and second pairs of walking legs.[14]
Ghost crabs utilize a varied animal acoustic communication system. They can create different sounds by striking the ground with their claws, rubbing their claws together to make a rasping sound, rubbing their legs to make a bubbly noise, and rubbing the teeth inside their stomachs to make a growling sound. The lateral teeth of the gastric mill possess a series of comb-like structures that rub against the median tooth to produce stimulation with dominant frequencies below 2 kHz.[15]
Ghost crabs also have the ability to change
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Atlantic ghost crab (Ocypode quadrata) emerging from its burrow in Cahuita, Costa Rica
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Horned ghost crab (Ocypode ceratophthalma) from a black sand beach in Kauai
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White sand beach inKahoolawe, Hawaii
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Sand Crab carrying eggs inCancun Mexico (Ocypodidae)
In a study in 1964, individuals of O. ceratophthalma in Hawaii from two populations (one from a black-sand beach and the other from a white-sand beach) were observed to markedly differ in pigmentation although they remain morphologically indistinguishable. Specimens taken from the black-sand beach were much darker than the specimens taken from the white-sand beach, exhibiting nearly 12 times as many black chromatophores. When the black-sand specimens were subsequently exposed to a white background, they were observed to gradually become lighter over the course of about a month. The opposite happened to white-sand specimens when placed in black backgrounds.[6]
In a 2013 study in Singapore, Ocypode ceratophthalma was also discovered to change color in response to the time of day. In a span of 24 hours, they were observed to alternate between lighter and darker coloration, being lightest at midday and darkest at night. However, when placed in a dark background, the crabs showed no significant changes in coloration. This suggests, at least for short-term color changes, they follow a day-night cycle to determine body coloration; basing it on their biological clocks rather than on the brightness or darkness of their environments. The researchers believe relying on the time of day rather than ambient light is more advantageous for survival in ghost crabs. It lets ghost crabs avoid changing color when in temporary shadow (for example within their burrows) and thus still remain inconspicuous when they are once again illuminated by daylight. However, this behavior is only exhibited by juveniles.[7][16]
Ghost crabs lay their
Distribution
Ghost crabs dominate sandy shores in
Conservation
Ghost crabs are negatively affected by human activity on sandy beaches, such as sand trampling by foot traffic, the building of seawalls, or the presence of inorganic pollutants. Due to their worldwide distribution and the ease by which their burrows can be surveyed, ghost crab burrows are regarded as valuable ecological indicators for quickly assessing the impact of human disturbance on beach habitats.[20][21][22]
See also
- Heloecius - the semaphore crab
References
- ^ ISBN 978-0-495-56197-2.
- ^ ISBN 978-0-521-30690-4.
- ^ ISBN 9780643069060.
- ^ S. Ajmal Khan; S. Ravichandran. "Brachyuran Crabs" (PDF). UNU-INWEH Course 1 - Training Course on Mangroves and Biodiversity, Institute for Water, Environment and Health, United Nations University. Retrieved November 7, 2013.
- ^ a b c d e f g h Katsushi Sakai; Michael Türkay (2013). "Revision of the genus Ocypode with the description of a new genus, Hoplocypode (Crustacea: Decapoda: Brachyura)" (PDF). Memoirs of the Queensland Museum – Nature. 56 (2): 665–793.
- ^ JSTOR 1539309.
- ^ .
- ^ Katsushi Sakai & Masatsune Takeda( with contributions from Peter J.F. Davie, Danièle Guinot, and Michael Türkay). "Subfamily Ocypodinae". Crabs of Japan, Marine Species Identification Portal. Retrieved November 7, 2013.
{{cite web}}
: CS1 maint: multiple names: authors list (link) - ^ Naturaliste Marine Discovery Centre. "Golden Ghost Crab". Government of Western Australia. Archived from the original on November 12, 2013. Retrieved November 12, 2013.
- ^ S2CID 81531389.
- ^ a b Smithsonian Marine Station's Field Guide to the Indian River Lagoon (2008–2011). "Ocypode quadrata". Smithsonian Marine Station at Fort Pierce. Retrieved November 12, 2013.
- ISBN 978-1-933251-31-8.
- hdl:2246/1016.
- ISBN 978-0-521-30690-4.
- PMID 31506058.
- ^ a b Ella Davies (April 5, 2013). "Horned ghost crabs change camouflage from day to night". BBC Nature. Retrieved November 8, 2013.
- ^ Sabrina Trocini (2013). Health assessment and hatching success of two Western Australian loggerhead turtle (Caretta caretta) populations (PDF) (Ph.D.). Murdoch University.
- ^ Brandon T. Barton (2009). Cascading effects of predator removal on the ecology of sea turtle nesting beaches (PDF) (Thesis). University of Idaho.
- ^ Nick Atkinson (September 27, 2008). "Don't Tread On Me". Conservation, University of Washington. Retrieved November 14, 2013.
- .
- .
- .
External links
- Taylor, Jennifer R. A., et al. “Growling from the Gut: Co-Option of the Gastric Mill for Acoustic Communication in Ghost Crabs.” Proceedings of the Royal Society B: Biological Sciences, vol. 286, no. 1910, 2019, p. 20191161., doi:10.1098/rspb.2019.1161.
- Martin Stevens, Alice Lown, Peter Todd & Cheo Pei Rong at the. "Camouflage and Colour Change in Ghost Crabs". Sensory Ecology & Evolution, University of Exeter. Archived from the original on 2015-09-19. Retrieved 2013-11-08.
{{cite web}}
: CS1 maint: multiple names: authors list (link) - Dennis DiClaudio (September 8, 2003). "The Nature of the Carolina Ghost Crab". Yankee Pot Roast.
- Video of Ocypode ceratophthalma eating a moon crab in Saint John's Island, Singapore
- ^ Taylor, Jennifer R. A., et al. “Growling from the Gut: Co-Option of the Gastric Mill for Acoustic Communication in Ghost Crabs.” Proceedings of the Royal Society B: Biological Sciences, vol. 286, no. 1910, 2019, p. 20191161., doi:10.1098/rspb.2019.1161.