Comprehensive Description
Vision
O. cordimanus is a ‘narrow-fronted’ species with closely-set compound eyes on long, vertically-orientated eye stalks raised high above the carapace (Ziel et al. 1986). These adaptations provide the animal with vision around three rotational axes and the advantage of being able to discriminate objects along the distant horizon of its flat-terrained, open habitat (Ziel et al. 1986). Raised eye stalks also enable the animal to remain partly submerged or concealed whilst maintaining an uninterrupted view of its environment (Ziel et al. 1986). 'Broad-fronted' decapods, such as species of the Family Xanthidae, have widely-spaced eyes on short stalks that suit a vegetated or rocky environment (Ziel et al. 1986).
Diet
Within their habitat, ghost crabs are positioned at the top of the food chain (Wolcott 1978). Their predators include birds and reptiles (Christoffers 1986), mammals (Wolcott 1978; Barton and Roth 2008), fish (Schlacher and Lucrezi 2010) and humans (Jackson et al. 1991). They display highly adaptable, opportunisitic feeding habits (Noriega 2008). The diet of ghost crabs consists of vegetable material, interstitial organic matter, intertidal macrofauna, turtle eggs and hatchlings (Hendrickson 1958), clams, mole crabs, shorebird chicks (Sabine et al. 2006); dead fish and other dead marine organisms (Wolcott 1978; Strachan et al. 1998; Sabine et al. 2006; Hickman et al. 2007; Noriega 2008).
Acoustics
Each species of ghost crab has a unique acoustic signature (Horch 1975). Male ghost crabs use a calling signal, rare among Crustacea, to attract females during the breeding season (Salmon 1972). O. cordimanus is acoustically active, predominantly at night during low tides around the new moon, and produces a rasping sound (Horch 1975) but along with O. sinensis, is one of only two species of the Ocypode genus lacking stridulatory organs on chelipeds (Huang et al. 1998). Sound is detected by Barth’s myochordotonal organ, a receptor located in the merus of each walking leg (Horch 1971). This organ is externally visible, marked by a thin-walled ‘window’ or ‘tympanum’ and helps the animal to detect higher-range frequencies that are impercetible to other sensory systems (Salmon 1972).
Activity
Ghost crabs are most active at night during low tides around the new moon (Horch 1975). They become less active at lower temperatures (Hughes 1966) and below 16˚C, some species become dormant or migrate inland (Christoffers 1986). The upper thermal limit for activity is around 30˚C (Weinstein and Full 1998).
O. cordimanus does not swim and is absent from pelagic habitats (Ruppert et al. 2004). Indeed, prolonged immersion in seawater can lead to osmotic stress ( ).
Mating
Female ghost crabs are exceptionally mobile and can roam for hundreds of metres during one feeding excursion (Christy 1987). Reproductively-active male ghost crabs reduce the energetic cost of searching for females by leaving the dunes to construct mating burrows in the supralittoral zone and using acoustic signals and sand piles to advertise their presence and attract females to them (Salmon 1972).
Lungs
Paired lungs are formed from expansion of the branchial chambers (Greenaway and Farrelly1984). Venous haemolymph is supplied to these from the body sinuses, oxygenated and then returned to the body via two main veins (Greenaway and Farrelly1984). Eye sinuses provide the influx of haemolymph to the lungs and this flows posteriorly to afferent vessels. Venous return is collected from both the gills and the lungs (Greenaway and Farrelly1984).
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