Ocypode+ceratophthalmus+(Pallas,+1772)


 * Basic Introduction**

Horn-eyed ghost crabs (//Ocypode ceratophthalmus//) are commonly found along the intertidal zones of sandy beaches in the tropics. These crabs are pale in colour with a dark H-shaped groove on the top and have distinctive horns on their eyes; hence it’s name. They are extremely fast runners with top speeds of 2.1m/s, the speed of crabs are often positively correlated with carapace width up to a certain size after which the weight of the crab slows it down.

They are also known to dig burrows in the sand. Beaches with ghost crab populations are often full of burrows; the deepest can reach up to 1.3m. Ghost crabs are not fussy eaters. They feed on carcasses, worms, fishes, clams, crabs and even their own species.


 * Classification**

( [|Pallas], 1772)  || ▪ // Cancer caninus // (Herbst, 1782) ▪ // Ocypode urvillei // (Guérin, 1829) ▪ // Ocypoda macleayana // (Hess, 1865) ▪ // Ocypode brevicornis var. longicornuta // (Dana, 1852) ||
 * [|Scientific classification]   ||
 * Kingdom: |||||| Animalia (Linnaeus, 1758) ||
 * Phylum: |||||| Arthropoda (Latreille, 1829) ||
 * Subphylum: |||||| Crustacea (Brünnich, 1772) ||
 * Class: |||||| Malacostraca (Latreille, 1802) ||
 * Order: |||||| Decapoda (Latreille, 1802) ||
 * Infraorder: |||||| Branchyura (Linnaeus, 1758) ||
 * Family: |||||| [|Ocypodidae], (Rafinesque, 1815) ||
 * Subfamily |||||| Ocypodinae ( Rafinesque, 1815) ||
 * Genus: |||||| [|//Ocypode//], (Weber, 1795) ||
 * Species: |||||| // O. ceratophthalmus // ||
 * [|Binomial name]   ||
 * // Ocypode ceratophthalmus //
 * [|Synonyms]   ||
 * ▪ // Cancer ceratophthalmus // (Pallas, 1772)
 * Vernacular names  ||
 * ** Common Name ** ||  ** Used in **  ||  ** Language **  ||
 * [|Agoyokoy] || Philippines || Cebuano ||
 * [|Ghost crab] || Hawaii || English ||
 * [|Horn-eyed ghost crab] || Philippines || English ||
 * [|Horned ghost crab] || USA || English ||
 * [|'ohiki] || Hawaii || Hawaiian ||
 * [|`o¯hiki] || Hawaii || Hawaiian ||
 * [|Bayokoy] || Hiligaynon || Philippines ||
 * Tsunome-gani || Japan || Japanese ||


 * Taxonomy and Etymology**

This species of was originally described as //Cancer ceratophthalmus// by Pallas in 1772, Latreille however shifted the species to Ocypode in 1810 and designated it as the type species. (Ng //et al.//, 2008) However, it is interesting to note that neither type specimen nor type locality has been mentioned in any papers.

The genus of this crab describes the speed of these crab, ocy- means swift in Greek and podos means foot, thus the crabs in this genus are swift-footed. Ceratophthalmus is used to describe the horns on top of the crab’s eyes as cer- means horned in Greek.

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 * Diagnosis**

Horn-eyed ghost crabs can be easily distinguished from other crabs by the horn-stalks on the eyes. Females have smaller shorter horns while the juveniles’ horns may not have any. The carapace is box-shaped with deep indentations to allow eyes to be kept. A distinct dark cervical groove (H-shape marking on the back) can also be found on the top of the carapace.

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 * Description**

Middle sized to large animals. Eyestalks extended beyond cornea (stylophthalmous). Exorbital corner laterally directed in large specimens. Stridulating ridge on inner surface of palm of major chela composed of about 13-16 distant striae in upper half and 20-30 close set ones in lower half. Small chela with both fingers pointed. Upper half of propodi of second and third pereiopods with a velvet. Male first pleopod slender, its distal part clearly bent laterally, palp with long and slender tip, its distance to pleopod tip slightly more than palp length. Opercle of female genital duct with depressed operculum, vulva-opening oblique with respect to median line of sternum, lateral rims not elevated. (Türkay 1995)

From eol website


 * Distribution and Habitat**

Horn-eyed ghost crabs are found throughout warmer climates i.e. the tropics and are native to regions ranging from East Africa to Australia. These crabs prefer sandy beaches and are commonly found within the intertidal zone, which are peppered with their burrows (Barrass, 1963; Serene, 1977). Crabs tend to select areas with access to water and sand consistency should be suitable for digging (Hughes, 1966). The map below shows the distribution of crabs across the globe.

Specific localities: Coco Island, Hawaii, Japan, Kenya, Madagascar, Malaysia, Mauritius, Mozambique, Philippines, Seychelles, Singapore, Somalia, South Africa, Tanzania, Red Sea, India, Maldives, Burma, Sumatra, Christmas Islands, Taiwan, China, Indonesia, New Britain, Australia, Solomon Island, Vanuatu, New Caledonia


 * Biology & Behaviour**

//Diet and Feeding Behavior//

Adult ghost crabs are voracious predators feeding on isopods, worms, sea cucumbers, prawns and other crabs (Jones, 1972). If given the opportunity these crabs are also cannibalistic especially of smaller crabs. Juveniles similarly predate on other species of crabs and insects (Hughes, 1966). Adults are mostly active at night while juveniles hunt in the day possibly to avoid cannibalism from larger individuals.

Ghost crabs have several methods of feeding (Hughes 1966):

1) Foraging

This is a general method of feeding where the crabs comb areas for food. Surprisingly, ghost crabs are able to detect the fine ridge left behind by the highest tidal wave. Crabs will comb the ridge looking for food, flipping obstacles such as rocks and sticks with their chelipeds. Any objects that moves are attacked and consumed if edible.

2) Scavenging

Horn-eyed ghost crabs are known to consume decomposing organic material. They have been observed to feed on dead fishes, crabs and other animals.

3) Sand Pellet Feeding

These crabs have been observed to sift through sand filtering out organic material and forming sand pellets in the process. The mouthparts have developed setae and a sizable maxilliped indicating proper adaption to shifting through sand (Jones, 1972).

4) Predatory feeding.

Ghost crabs with their elongated eyestalks hunt for prey visually. The legs of the prey that are able to escape are bitten of to prevent escape. Small preys are consumed on the spot, while larger ones will be brought back to the burrow. Juveniles prefer insects, small crabs such as ocypodes and pagurid. Adults on the other hand prey on prawns, isopods, annelids and crabs such as Portunids, Calappa and Uca.

5) Cannibalism

Larger individuals cannibalise on smaller ones.

6) Donax Feeding

Horn-eyed ghost crabs are able to precisely located buried clams (//Donax faba// and //D. incarnate//). These clams are then excavated using two walking legs on each side. The extracted clams are then crushed by the chelipeds and the flesh consumed. Most adult crabs are able to crush shells less then 12mm in anterior-posterior length. If the clam is too large, the crab will try to break the edges and attempt to pry it open by maneuvering the cheliped within the shell. If the clam densities are high, the crab might abandon tough clams for easier targets.

//Burrowing//

The many burrows scattered along the beach during low tide is usually an indicator of ghost crabs. Burrowing behaviour has been clearly documented and each burrow is observed to house only one crab.

Show video from sgbeachbum

Crabs have been observed to burrow in areas where the sand is not too hard or too soft for excavation. When a crab emerges from the burrow, it carries a mass of sand with its smaller cheliped and legs. The sand is carried away from the burrow (<1m) before dropping it before returning to its burrow. Sand surrounding the entrance of burrow is compacted and flattened using its legs and chelipeds (Barrass, 1963). This makes the entrance of the burrow level with the surrounding terrain.

Adult burrows have been found to be clockwise or anti-clockwise. It seems that crabs with larger right chelipeds dig clockwise burrows while crabs with larger left chelipeds dig anti-clockwise burrows (Barrass, 1963). This directionality of the burrows might allow the most freedom for the larger cheliped should the cab need to defend it’s burrow (Hughes, 1966). This is similar to the structure of stairways in medieval castles which favored the righthanded defenders (Hughes ,1966).

Burrows of juveniles (<2cm carapace width) on the other hand showed no particular fixed pattern. Burrows ranged from straight to curve and of varying depths. Depth of burrows is often depending on the period of time available for digging and its location on the beach; the higher the position of the burrow on the beach the deeper the burrow. Excavated sand can be disposed of in several ways; from organized heaps away from the burrow to radial dispersal around the entrance. In all cases, sex of the crab does not affect the type of burrow constructed (Hughes, 1966).

Besides having directionality, three different types of burrows have been observed too.

1) Emergence burrows

These burrows are range from 20-25cm and not deeper as difficulty of digging increases as the sand gets more compact.

2) Open burrows

Open burrows ranging from 0.3-1.3m deep are used as a platform for scavenging or digging. Construction of these burrows involves the removal of sand, which is done radially from the burrow. And this is mostly carried out in the day where predators can be seen. Should excavation be carried out at night, sand will be piled near the entrance of the burrow. These burrows are built when the area where the crab forages is submerged or if the crab leaves its burrow earlier then usual. It can also occur if crabs change their emergence burrow to that of an open burrow to forage from that area. Crabs returning with food before the next high tide may also build these burrows.

3) Covered burrows

This is often dug in haste such as in the case of rising tides. Crabs dig directly into the sand and covering the entrance as they burrow in.

//Threats/Social interactions//

If a crab is threatened by other species, it assumes a threat posture that is displayed by raising itself on the last three pairs with the cephalothorax vertically positioned. Chelipeds are placed in front of the carapace. With this posture, the crab attempts to enhance its size visually to intimidate the threat (Jones, 1972).

If faced with another crab of the same species, the response of the crab depends on the size of the other. If the opposing crab is of a smaller size, the crab will overpower and devour it. The smaller crab will attempt to escape if possible. If crabs are evenly matched in terms of size, the crabs will enter a faceoff where the threatened posture will be adopted to intimidate its opponent. Should the opponent be unfazed, crabs will start “paddling” chelipeds followed by swift strikes at the opponent using their chelipeds. However, these actions occur within a short amount of time; after striking at each other, crabs will retreat to their own burrow or run away.

//Stridulation//

The purpose of stridulating is to act as a warning signal to other crabs. It is to send the message to others that the burrow is occupied to fend off intruders or to possibly attract mates (Barrass, 1963; Hughes, 1966). Ghost crabs stridulate by rubbing the tubercles on the inner face of the propodus of the larger cheliped against a ridge on the ischium (Hughes, 1966). Crabs of this species can produce 3 different types of sound.

1) The most commonly heard sound is a rapid rattling sound consisting of three to seven rasping sound which goes by Krr-Krr-Krr-Krr-KirriKrr.

2) Another sound made is a burbling bubbling noise which last for a few seconds and produced at increasing volume.

3) The third is multiple strong knocking sound which is can be heard up to 20m away.

//Reproduction//

Currently no proper documentation of mating behavior

References:

Holthuis, L. B., 1962. Forty-seven genera of decapoda (Crustacea); Proposed addition to the official list. Z.N.(S.) 1499. //Bulletin of Zoological Nomenclature.// **19**: 232-252.

Jones, D. S., 1988. The Occurrence of Ocypode pallidula Jacquinot (Decapoda, Brachyura) in Australia and the Coral Sea. //Crustaceana//. **54**(1): 33-38 Serene, R. (1977). Crustaces Hippides et Brachyoures des iles Sechelles. // Revue de Zoologie Africaine //. ** 91 ** (1): 45-68.

Barrass, R., 1963. The burrows of Ocypode ceratophthalmus (Pallas) (Crustacea, Ocypodidae) on a tidal wave beach at Ihaca Island, Moçambique. //Journal of Animal Ecology//. **32**(1): 73-85.

Jones, D. A., 1972. Aspects of ecology and behavior of Ocypode ceratophthalmus (Pallas) and O. Kuhlii de Haan. (Crustacea: Ocypodidae). // Journal of Experimental Marine Biology and Ecology //. **8**: 31-34.

Hughes, D. A., 1966. Behavioural and ecological investigations of the crab Ocypode ceratophthalmus (Crustacea: Ocypodidae). Journal of Zoology (London). **150**: 129-143.